Qualification:
Ph.D
v_ratnakishore@cb.amrita.edu

Dr. Ratna Kishore V. received his Ph. D. in Mechanical engineering from Indian Institute of Technology, Delhi (IITD) in 2010. His dissertation was titled, Experimental and Computational Investigations on Open Laminar Flames of Multi-Component Gaseous Fuel Mixtures. The objective of this research is to study the laminar burning velocity using Heat Flux Method, effect of stretch diffusive-thermal instability of multi-component fuel mixtures burning in air (21% O2 & 79% N2 by volume). The work also involves flames simulations for 2D slot burners and 3D flat flame burner using FLUENT. Dr. Ratna Kishore has published 5 research articles in international journals and 5 at international conferences.

His current areas of research are: Premixed Combustion for Multi-components Mixtures (for ex. Propane + hydrogen), High Temperature Natural Convection Flows and Flow through industrial valves.

## Education

• 2013: Ph. D. in Mechanical Engineering
Indian Institute of Technology, Delhi
• 2004: M. Tech. in Thermal Engineering
Indian Institute of Technology, Delhi
• 2002: B. Tech. in Mechanical Engineering
National Institute of Technology, Surathkal

## Professional Appointments

Year Affiliation
November 2016 - Present Associate Professor, Department of Mechanical Engineering, School of Engineering, Amrita Vishwa Vidyapeetham, Coimbatore
January 2011 - November 2016 Assistant Professor, Department of Mechanical Engineering, School of Engineering, Amrita Vishwa Vidyapeetham, Coimbatore
August 2002 - May 2010 Teaching Assistant, IIT Delhi, New Delhi, India

## ​​​​​Reviewer in Journals/ Conferences

Dr. Ratna Kishore V. is involved in the reviewing of research papers/ articles as follows:

• International Journal of Hydrogen Energy
• Energy, An International Journal
• International Journal of Thermal Sciences
• IMechE: Institution of Mechanical Engineers, Journal of Aerospace Engineering, Part G
• Renewable and Sustainable Energy Reviews
• International Journal of Renewable Energy Research
• Journal of Nanomaterials

## Courses Handled - Theory

UG Level PG Level
Gas Dynamics and Jet Propulsion Design of Thermal Systems
Computational Fluid Dynamics Applied Mathematics
Thermodynamics
Fluid Mechanics and Machinery

## Thrust Area of Research

Combustion, CFD, Compressible flow, Wind Turbines

## Teaching/Research Interests

Major Subjects Taught

• Computational Fluid Dynamics
• Heat Transfer
• Thermodynamics
• Gas Dynamics

Research Interests

• Combustion
• CFD
• Compressible Flow
• Wind Turbines

## Publications

### Publication Type: Journal Article

Year of Publication Title

2021

U. Divakaran, Dr. Ajith Ramesh, Mohammad, A., and Dr. Ratna Kishore V., “Effect of Helix Angle on the Performance of Helical Vertical Axis Wind Turbine”, Energies, vol. 14, no. 2, p. 393, 2021.[Abstract]

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2021

A. B Narayanan, Lakshmanan, G., Mohammad, A., and Dr. Ratna Kishore V., “Laminar Flow over a Square Cylinder Undergoing Combined Rotational and Transverse Oscillations.”, Journal of Applied Fluid Mechanics, vol. 14, no. 1, 2021.[Abstract]

This work numerically investigates the effects of combined rotational and transverse oscillations of a square cylinder on the flow field and force coefficients. The primary non-dimensional parameters that were varied are frequency ratio fR (0.5, 0.8), Re (50-200), phase difference (ϕ) between the motions and rotational amplitude (θ0) with the influence of the last three parameters being discussed in detail. The amplitude of transverse oscillations is fixed at 0.2D, where D is the cylinder width. The study has been validated using the mean drag coefficient for stationary and transversely oscillating square cylinders from literature. Output data was obtained in the form of force coefficient (Cd), vorticity and pressure contours. The governing equations for the 2- dimensional model were solved from an inertial frame of reference (overset meshing) using finite volume method. The interplay between the convective field and prescribed motion has been used to explain many of the results obtained. The relative dominance of cylinder motion over the flow stream was determined using Discrete Fast Fourier Transform. The influence of Re on Cd disappears when the motions are completely out of phase (ϕ = π). In general, the Cd for low Re flows exhibited low sensitivity to change in other parameters. Direct correlation has been observed between frontal area, vortex patterns and drag coefficient,

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2021

G. T Prasad, Jithin, E. V., Varghese, R. John, Kumar, S., Mohammad, A., and Dr. Ratna Kishore V., “Effect of hydrocarbon addition on tip opening of hydrogen-air bunsen flames”, International Journal of Hydrogen Energy, vol. 46, no. 7, pp. 5763–5775, 2021.[Abstract]

The effect of hydrocarbon addition on tip opening of lean and stoichiometric hydrogen-air flames is studied computationally by performing two-dimensional numerical simulations. The numerical study reveals that the flame tip of the H2-air burner stabilized flame is open at lean and stoichiometric mixture conditions. The flame tip closes upon hydrocarbon addition. The tip closing is mainly affected by preferential diffusion of the multi-component mixture and the stretch effects. In the addition of light hydrocarbon (CH4), the tip closing starts at a higher percentage of hydrocarbon addition in H2-air flames. Whereas, upon the addition of heavy hydrocarbons such as propane and butane in H2-air flames, tip closing starts with a lesser amount of hydrocarbon addition. Temperature, OH mole fraction and heat release rate have been investigated, focusing on the flame structure at the tip. The tip opening regime diagram for H2–CH4-air, H2–C3H8-air and H2–C4H10-air mixtures are presented.

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2021

H. Sivanandan, Dr. Ratna Kishore V., Goel, M., and Asthana, A., “A Study on Plume Dispersion Characteristics of Two Discrete Plume Stacks for Negative Temperature Gradient Conditions”, Environmental Modeling & Assessment, pp. 1–18, 2021.[Abstract]

The dispersion of air pollutants emitted from industries has been studied ever since the dawn of industrialisation. The present work focuses on investigating the effect of negative atmospheric temperature gradient and the plume stack orientation of two individual equal-height stacks on the vertical rise and dispersion of the plume. The study carried out upon three-stack layout configurations namely inline, 45° and non-inline, separated by an inter-stack distance of 12 times the exit chimney diameter (12 D) and 22 times the exit chimney diameter (22 D) in each case over the two temperature gradients of −0.2 K/100 m and −0.5 K/100 m. The turbulence is modelled using realisable k-ε model, a model used in the FLUENT flow solver. In the case of the inline configuration, the upwind plume shields its downwind counterpart, which in turn allows for higher plume rise at a given temperature gradient. The plume oscillates more in the case of inline than 45° and non-inline cases. Also, for a temperature gradient of −0.5 K/100 m, the plumes oscillate violently in the vertical direction, mainly because, with the initial rise of the plume, cold air from higher altitudes moves down and forms a layer of lower temperature closer to the ground. The present study is important to highlight the plume dispersion characteristics under negative temperature gradient conditions.

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2021

R. Kumar, Dr. Ratna Kishore V., and Kumar, S., “Combustion of methylcyclohexane at elevated temperatures to investigate burning velocity for surrogate fuel development”, vol. 406, p. 124627, 2021.[Abstract]

To overcome the complexity associated with the development of detailed kinetic models for real transportation fuels, surrogate fuel models offer an excellent alternative. The present study reports laminar burning velocity (LBV) measurements of methylcyclohexane (MCH)&nbsp;+&nbsp;air mixtures for mixture temperatures up to 610&nbsp;K using externally heated diverging channel method (EHDC) method at 1&nbsp;atm pressure. MCH is a commonly used surrogate blend for aviation fuels, gasoline, and diesel, whose kinetic model is simpler to develop. The measurement of laminar burning velocity forms the basis of kinetic model development for such surrogate fuels. The present work reports the measured LBV values for an equivalence ratio range, φ&nbsp;=&nbsp;0.7–1.4, and their comparison with available experimental data and detailed kinetic model predictions for a mixture temperature range, 353–610&nbsp;K. Temperature exponent, α is derived using the power-law correlation and good consistency with kinetic model predictions is observed up to 500&nbsp;K mixture temperatures. At 610&nbsp;K mixture temperature, an overprediction of ≈12% at φ&nbsp;=&nbsp;1.05 is observed with JeTSurF 2.0 (2010) model and 27% overprediction with the kinetic model of PoliMi (2014) φ&nbsp;=&nbsp;1.1. Overall, the reported LBV measurements show slightly better match with the JeTSurF 2.0 (2010) kinetic model than the Wang (2014) kinetic model. Reaction pathway diagrams are drawn to highlight the importance of C2H4 and C2H3 radicals for an increase in the overall reaction rate at 610&nbsp;K.

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2020

P. Murugesan, Kumar, A. Biju, Kambhampati, A. Teja, Pillai, S., Chandrasekar, G. Chandar, Raghavannambiar, S. Ambattu, and Dr. Ratna Kishore V., “Numerical Study of Characteristics of Underexpanded Supersonic Jet”, Journal of Aerospace Technology and Management, vol. 12, 2020.[Abstract]

Correlations for the supersonic jet characteristics, the mean shock cell length and the supersonic core length, have been obtained in terms of the jet parameters. The jet parameters considered in this study are the exit diameter of the nozzle (de), the design Mach number (Me), the nozzle pressure ratio (NPR) and the ratio of specific heats of the medium (γ). The parameters were varied as follows: exit diameters, from 0.5 to 25 mm; Mach number from 1 to 3; the NPR from 2.14 to 35. Initially, working fluid used is cold air and then effect of variation of γ is taken into consideration. The computational model has been validated and then used for all the numerical simulations. A quadratic fit for both characteristics has been obtained which is applicable to any supersonic jet. The correlations developed are valid within the respective ranges of the parameters stated above.

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2020

P. Singh, Dr. Ratna Kishore V., and Chander, S., “A Numerical Investigation on Fluid Dynamics and Heating Characteristics of Co-and-Counterrotating Multiple Swirling Impinging Flames Arranged in 3$\times$ 3 Inline Array”, Journal of Thermal Science and Engineering Applications, vol. 12, no. 3, 2020.[Abstract]

Swirling impinging flame jets possess the potential of uniformly heating the target surface. Numerical simulations have been carried out for multiple reacting swirling flows arranged in square 3 × 3 array. The turbulence chemistry interactions in the flow field are modeled using RNG based k-ε/ eddy dissipation model (EDM) framework. Co-and-counterrotating configurations have been compared for interactions and spent gas release mechanism at fixed inter-jet spacing and separation distance. Multiple swirling impinging flames undergo strong interactions resulting in distortions of recirculation zones (RCZs) for all the surrounding but central flame. Co-swirling flames result in development of higher turbulence in the interaction regions as compared with counter-swirl case. Tilted heat flux contours have been noticed for co-swirling impinging flames, whereas heat flux impressions are straight for counter-swirl case. Effect of inter-jet spacing (C/Dh = 5, 7, and 9) and separation distance (H/Dh = 3, 5, 7, and 9) studied for co-swirl case revealed that peak heat fluxes decreased with increasing inter-jet spacing and separation distance. With increase in inter-jet spacing, the width of central flame increased due to increased suppression effect induced by the recirculating gases. Increase in separation distance resulted in decrease of width of central flame and thermal dilution taking place led to decrease in heat flux magnitudes.

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2020

E. V. Jithin, Varghese, R. J., and Dr. Ratna Kishore V., “Experimental and numerical investigation on the effect of hydrogen addition and N2/CO2 dilution on laminar burning velocity of methane/oxygen mixtures”, International Journal of Hydrogen Energy, vol. 45, no. 33, pp. 16838–16850, 2020.[Abstract]

An experimental and numerical study on the combined effect of N2/CO2 dilution and hydrogen addition on the laminar burning velocity (LBV) of methane-oxygen mixtures was conducted. The experiments were performed at atmospheric conditions using the heat flux method for effective equivalence ratios (ϕF) varying from 0.7 to 1.3. The results show that the hydrogen addition causes an increase in LBV for all the mixture conditions. The variation in LBV based on hydrogen addition parameter (RH) for all N2 dilution conditions were following a linearly increasing trend. The strong effect of hydrogen addition on LBV is observed at lean and rich mixtures compared to that at near stoichiometric mixture conditions. The experimental results show that the percentage variation in LBV with RH at rich mixture is more substantial at 75% N2 dilution compared to that at 65% N2 dilution.

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2020

P. Singh, Dr. Ratna Kishore V., and Chander, S., “Computational Fluid Dynamics Analysis of Aerodynamics and Impingement Heat Transfer From Hexagonal Arrays of Multiple Dual-Swirling Impinging Flame Jets”, Journal of Heat Transfer, vol. 142, no. 8, 2020.[Abstract]

Radiative furnaces pose significant thermal inertia and single impinging flames have been observed to cause occurrence of hotspots on the target surface. Multiple burners arranged in suitable array configuration represent one of the plausible solutions for more uniform heat transfer. In this study, computational fluid dynamics (CFD) simulations have been carried out for multiple swirling impinging flames arranged in a hexagonal array configuration. The turbulence chemistry interactions in the flame field are solved numerically using renormalization group (RNG) based k–ε/eddy dissipation model (EDM) framework. Comparison of co-and-counter-swirling configurations has been studied for interactions and spent gas release mechanism. Multiple swirling impinging flames undergo strong interactions resulting in distortions of recirculation zones (RCZ) for all the surrounding except central flame. Co-swirling flames result in development of higher turbulence in the interaction regions as compared to counter-swirl case. Results indicate that some flames in counter-swirl case are underutilized due to the fluid dynamics developed in the system and co-swirling hexagonal array configuration is a better arrangement for effective heating of target surface. Effect of interjet spacing (S/Dh = 5, 7, and 9) and separation distance (H/Dh = 3, 5, 7, and 9) studied for co-swirl case revealed that peak heat fluxes decreased with increasing interjet spacing and separation distance. Central flame represented a region of low heat flux and this region has been noticed to expand in size for increasing interjet spacings. Suppression of central flame has been observed to be maximum for minimum separation distance.

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2020

A. Muraleedharan, Jithin, E. V., Aravind, B., Kumar, S., and Dr. Ratna Kishore V., “Combustion characteristics of syngas laminar microjet diffusion flames”, Journal of the Taiwan Institute of Chemical Engineers, vol. 115, pp. 47 - 59, 2020.[Abstract]

Two-dimensional numerical investigations of laminar microjet syngas (H2 - CO) diffusion flames are carried out in the present study. A detailed parametric study on the effects of fuel jet velocity and fuel composition on global flame characteristics is analyzed. Results show that the flame height increases with an increase in fuel jet velocity, and it decreases with an increase in hydrogen content in the fuel mixture. The dependence of fuel composition and jet velocity on the rate of tube wall heat recirculation is explored. The radial extent of flame increases with increase in hydrogen content in the fuel mixture. The analysis of key reactions in the standoff region revealed the significant contribution of HO2 radical in the formation of high-temperature reaction zone. Flame extinction is observed at lower fuel jet velocities, as the composition of hydrogen in fuel mixture increases from 10 to 90%. Near extinction, the combined effect of axial and radial diffusion results in the formation of spherically shaped flames.

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2020

K. Hiranandani, Aravind, B., Dr. Ratna Kishore V., and Kumar, S., “Development of a numerical model for performance prediction of an integrated microcombustor-thermoelectric power generator”, vol. 192, p. 116624, 2020.[Abstract]

This paper presents the development of a numerical model for a thermoelectric generator integrated with a novel microcombustor to predict the thermoelectric performance of the system. The novelty of the work lies in the development of a numerical model to predict and analyze the system’s thermal characteristics and thermoelectric performance with numerical simulations. The system consists of a microscale combustor and two Bi2Te3 thermoelectric modules mounted on the combustor. The combustor has backward facing steps and a recirculating cup to enhance its flame stability and thermal characteristics over other combustors. Following the thermal analysis of the microcombustor, the model for predicting the power output from the thermoelectric modules is validated and then integrated by using separate sub-routine. A maximum open-circuit voltage of 8&nbsp;V was reported for the integrated system. For a load resistance of 2.8&nbsp;Ω, a power output of 5.6&nbsp;W was obtained at a conversion efficiency of 6.8%. It can be concluded that the successful integration of a thermoelectric model into CFD software will provide great impetus to future studies on thermoelectric generators, while the optimized combustor, with a volume comparable to that of a dry cell, can serve as a viable replacement for electrochemical batteries.

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2020

P. Singh, Dr. Ratna Kishore V., and Chander, S., “Experimental and Computational Analysis of a Row of Three Co-swirling Impinging Flames”, Heat and Mass Transfer/Waerme- und Stoffuebertragung, vol. 56, no. 2, pp. 365-384, 2020.[Abstract]

Detailed flow field and heat transfer characteristics developed in a row of three co-rotating dual swirling impinging flames have been investigated experimentally as well as numerically. Impingement heat transfer and pressure distribution has been studied experimentally at different separation distances and inter-jet spacings. Inverse heat conduction procedure (IHCP) has been used for estimating heat fluxes on the front side of impingement plate. Turbulence induced mixing results in strong interactions amongst adjacent flames causing deflections of inner flames of the burners situated at sides of central burner. Numerical simulation predicted formation of asymmetric recirculation zones for side flames. Symmetric interactions taking place for central flame produced two equal recirculation lobes for central flame. Behavior of central inner flame has been observed to be dependent on the value of inter-jet spacing used. Suppression of central inner flame tend to occur at higher inter-jet spacings due to recirculating products. Impingement pressure distribution is observed to be consistent with the heat flux distribution. Averaged heat fluxes registered at the impingement plate due to the central flame are higher in magnitude to those pertaining to each of the side flames.

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2019

Unnikrishnan D., Dr. Ratna Kishore V., and Dr. Ajith Ramesh, “Effect of wind speed on the performance of Troposkein Vertical axis wind turbine”, International Journal of Renewable Energy Research (IJRER), vol. 9, no. 3, pp. 1510–1521, 2019.[Abstract]

Wind energy being one of the renewable energy sources, having potential to substitute power generation from fossil fuels, has always drawn the spot light of research society. Non-straight bladed vertical axis wind turbine (VAWT) has proven to be one among the better options among small scale turbines. The presented work investigates the effect of wind speed on the performance of a Troposkien blade VAWT using 3D CFD simulations. The transitional SST K-w model is used for modeling turbulence. Simulations are conducted for varying wind velocities (6 m/s - 14 m/s) and varying tip speed ratios (TSR) (1.6 - 2.1). Based on the swept area of the turbine, the mean radius of the turbine is calculated which serves as the basis for the calculation of TSR. The results obtained indicate that the turbine performance is significantly affected at lower TSR at varying wind speeds, and the percentage of change is much lower at higher TSR values. Peak performance of the turbine is noted at the same TSR value for all wind velocities, and the magnitude of coefficient of performance is found to be almost the same.

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2019

Dr. Ratna Kishore V., Sankar, V., and , “Effect of Hydrogen Addition on Laminar Burning Velocity of Liquefied Petroleum Gas Blends”, Energy & Fuels, vol. 34, no. 1, pp. 798-805., 2019.[Abstract]

The consequences of H2 enrichment on the laminar burning velocity (LBV) of various liquefied petroleum gas (LPG) blends have been studied experimentally and numerically. The study was carried out at various equivalence ratios (ϕ) (from 0.8 to 1.3 in steps of 0.1). Experiments were conducted on various LPG blends, by adding hydrogen up to 60% by volume in steps of 20, using the heat flux method (HFM) experimental setup. A detailed computational study was conducted using a PREMIX code to predict the LBV and to explain the flame structure of LPG–hydrogen–air mixtures. LBV predictions using two different chemical kinetic mechanisms such as Aramco Mech 2.0 and USC Mech II mechanism were compared with experimental results of the LBV for all the fuel mixture compositions studied. The LBV predicted by the Aramco Mech 2.0 mechanism matched well with the present experimental results. The LBV of the LPG–air mixture was observed to be increasing upon hydrogen addition. A linear increase in the LBV upon hydrogen addition was observed until 40% H2 addition in the fuel mixture. The effect of hydrogen addition was found to be more significant at 60% H2, showing a nonlinear increase in the LBV from 40 to 60% H2 addition. The effect of hydrogen addition on the LBV was observed to be prominent in the rich mixture side. The variation in the LBV with hydrogen enrichment was found to be dependent on the concentration of C3H8 in the fuel mixture. The effect of the composition of propane and butane on the LBV of LPG was also studied. The laminar burning velocity at elevated temperatures was measured using a diverging channel setup for LPG (60% C4H10–40% C3H8) at various H2 compositions. The temperature exponent was found to be decreasing with the hydrogen addition. The minimum value of the temperature exponent for all the studied mixture compositions was observed at ϕ = 1.1.

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2019

R. John Varghese, Kolekar, H., Dr. Ratna Kishore V., and Kumar, S., “Measurement of Laminar Burning Velocities of Methane-air Mixtures Smultaneously at Elevated Pressures and Elevated Temperatures”, Fuel, vol. 257, p. 116120, 2019.[Abstract]

Externally heated diverging channel method helps accurate and direct measurement of laminar burning velocities at elevated temperatures. In the present work, this method has been extended to higher pressures to evaluate the combined effect of pressure and temperature on the propagation of premixed methane-air flames. The experimental measurements of methane-air mixtures for different equivalence ratios are reported for a pressure range (1–5 atm), and elevated temperatures of 350–650 K. A non-monotonic behaviour for temperature exponent, α is obtained with a minimum value for slightly rich mixtures (ϕ = 1.1). This non-monotonic behaviour of α continues even at higher pressures (2–5 atm) as well. Predictions from three widely used chemical kinetic mechanisms (GRI-Mech 3.0, Aramco 2, FFCM-1) are employed to compare with present experiments. LBV determined using Aramco 2 mechanism matches very well with the present measurements at various elevated pressures and mixture conditions. The variation of pressure exponent, β follows a bell-shaped curve with maximum value for slightly rich mixtures (ϕ = 1.1) and a peculiar non-linear behaviour for very rich mixtures (ϕ ≥ 1.3). Based on the detailed analysis of experimental results, the temperature exponent (α) is proposed as a function of pressure, and pressure exponent (β) as a function of temperature at various equivalence ratios. A modified power-law correlation considering the α,β variations is proposed: Su=Su,oTuTu,oαo+α11-PuPu,oPuPu,oβo+β11-TuTu,o. Analysis of the flame structure at high-pressure conditions indicates that the reaction layer thickness is reduced with an increase in pressure. A decrease in mixture thermal diffusivity with pressure contributes to a reduction in laminar burning velocity at elevated pressures.

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2019

P. Singh, Dr. Ratna Kishore V., Prathap, C., Mohammad, A., and Chander, S., “Study of Flow Patterns and Impingement Heat Transfer for an Annular Array of eight C-rotating Dual-swirling Flames”, International Journal of Heat and Mass Transfer, vol. 144, p. 118657, 2019.[Abstract]

Performance of gas burners can be optimized by improvements in their design and proper selection of operating parameters associated with combustion and heat transfer mechanisms. Array of multiple swirl burners is one such configuration where uniformity in heat transfer can be increased significantly. The current study presents experimental and numerical investigations conducted for flow patterns and impingement heat transfer developed in an annular arrangement of eight co-rotating dual swirling impinging flames. Impingement heat flux distribution has been studied experimentally using analytical inverse heat conduction procedure (IHCP). Effect of change in separation distance and inter-jet spacing has been studied for interactions and subsequent impingement heat transfer characteristics. Turbulent co-swirling flames portray intense mixing developed at the interaction regions due to strong interactions. Presence of impingement plate causes large scale changes in the flow-field. Numerical simulation conducted under reacting conditions predicted formation of asymmetric and distorted recirculation zones. Inner flames have been observed to deflect from their straight upright positions. Adjacent co-swirling flows merge together and develop circulation of flow at the inner periphery of the annulus. High heat fluxes observed at the target surface are corresponding to interaction regions and tend to cluster around the geometric centre of the array. Reversed downward flow developed at the geometric centre represents region devoid of heating. Averaged heat fluxes registered at the impingement plate decreased with increasing inter-jet spacing and separation distance. Maximum uniformity in the heat transfer has been observed at inter-jet spacing, S/Dh of 4 and separation distance, H/Dh of 6.

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2019

N. Srivastava, Aravind, B., Dr. Ratna Kishore V., Minaev, S., and Kumar, S., “Numerical Investigations on Behaviour Bifurcation of Premixed H2-air Flames in Mesoscale Tubes”, Combustion Theory and Modelling, vol. 23, pp. 969-993, 2019.[Abstract]

Unsteady numerical simulations with detailed kinetic chemistry have been reported for premixed H2-air flames in straight mesoscale tubes of various diameters to understand the effect of wall heat transfer conditions on flame transition and behaviour bifurcation leading to a change in flame shape and flame propagation velocity. A parabolic velocity profile is applied with no-slip boundary conditions at the walls. For certain wall heat transfer conditions, it was observed that the flame transforms from a concave- to convex-shaped flame during propagation through the channel, accompanied by a change in flame propagation speed, heat of reaction and heat release rates. The transition in flame shape is attributed to thermal wall coupling effect through wall heat transfer to surroundings, which affects the flow redirection in the vicinity of the flame due to heat-loss, resulting in flame behaviour transition. Due to these flame behaviour transitions, the heat release rates and flame propagation velocities change significantly as discussed in this paper.

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2019

K. S. Rajan, Mukherjee, S., R Raj, G., Dr. Ratna Kishore V., and Shahabi, V., “Effect of Knudsen Number, lid Velocity and Velocity Ratio on Flow Features of Single and Double lid Driven Cavities”, Journal of Applied Fluid Mechanics, , vol. 12, no. 5, pp. 1575-1583, 2019.[Abstract]

Effects of Knudsen number, lid velocity and velocity ratio are investigated on the flow features of single lid driven cavity with an aspect ratio of one and double lid driven cavity of aspect ratio two. Knudsen numbers studied are 0.01(early slip regime), 0.1 (slip regime) and 1 (transitional regime). Lid velocities investigated are 100 m/s, 200 m/s and 500 m/s. The velocity ratios explored are 1 and -1. Knudsen number was found to have a huge impact on the flow rigidity. Lid velocity tends to shift the central vortex to the top left of the cavity for a cavity with aspect ratio of one and shifts the upper vortex to the top left of the cavity for a cavity with aspect ratio of two. Lid velocity does not affect the slip to a great extent on the lid. Changing the velocity ratio from 1 to -1 leads to the reversal of the relative vorticity in the top and bottom half of the cavity.

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2019

A. S. Prakash, Ram, K. S., and Dr. Ratna Kishore V., “Aeroacoustics Analysis of Globe Control Valves”, International Journal of Automotive and Mechanical Engineering, vol. 15, no. 3, pp. 5547-5561, 2019.[Abstract]

Flow-induced noise in control valves is one of the greatest challenges faced by several industries and commonly used flow control device in process industries is globe control valves (GCV). In the present work numerical analysis was performed to study aeroacoustics of globe control valve. Axisymmetric globe control valve (2.54 cm) was analysed numerically using 2D large eddy simulation (LES) turbulence model for different valve openings. The Ffowcs-Williams and Hawkings (FWH) model was used to model the aero-acoustic. The fluid medium in the valve is air. It was observed that the sound pressure level (SPL) decreases with increase in the opening of the valve. The modification in the design of the control valve was considered to reduce SPL without affecting the inherent characteristic, flow coefficient (C<sub>v</sub>). The design modifications in the control valve considered were chamfering the seat and filleting the plug of the valve. Out of these modifications, the 20° chamfer to the inlet side of seat gave the least sound pressure level for the various openings of the globe control valve.

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2019

B. Mantravadi, Unnikrishnan D., Sriram, K., Mohammad, A., Dr. Laxman Vaitla, and Dr. Ratna Kishore V., “Effect of Solidity and Airfoil on the Performance of Vertical axis wind Turbine Under Fluctuating wind Conditions”, International Journal of Green Energy, vol. 16, no. 14, pp. 1-14, 2019.[Abstract]

ABSTRACTVertical axis wind turbines (VAWTs) are frequently subjected to fluctuating winds in urban environments. In this paper, we studied the effect of airfoil thickness and solidity on the performance of VAWT under fluctuating wind conditions using three-dimensional computational fluid dynamics model with transition SST turbulence model. In this work, NACA 0012, 0015, and 0030 airfoils; two- and three-bladed VAWT are studied. The performance of VAWT is analyzed by varying fluctuation amplitude and frequency. From the results, it is observed that the cycle averaged CP increases with increase in fluctuation amplitude and airfoil thickness. For two-bladed VAWT, the cycle averaged CP reduces with fluctuation amplitude. In contrast, CP increases with fluctuation amplitude for three bladed. In case of fluctuation frequency, all the airfoils exhibited similar trend. The cycle averaged CP increases to a maximum value corresponding to fc&nbsp;=&nbsp;1&nbsp;Hz and then decreases with fc. NACA 0030 airfoil curve exhibits relatively higher CP and a uniform performance when compared to that of NACA 0012 and 0015. If the fluctuating wind is characterized by continuous change of frequency, it is desirable to employ the three-bladed VAWT and NACA 0030 air foil for better performance. This work intends to help during the design of VAWT under fluctuating wind conditions.

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2019

E. V. Jithin, Dinesh, K., Mohammad, A., and Dr. Ratna Kishore V., “Laminar Burning Velocity of n-butane/Hydrogen/Air Mixtures at Elevated Temperatures”, Energy, vol. 176, pp. 410-417, 2019.[Abstract]

The effect of hydrogen (H 2 ) addition in the laminar burning velocity (LBV) of n-butane-air at elevated temperatures is described in this paper. For various equivalence ratios (ϕ), ranging from 0.7 to 1.3, LBV was measured for 20%, 40% and 60% H 2 addition to n-butane using a preheated mesoscale diverging channel technique. Using this experimental technique, LBV measurements were conducted for unburnt mixture temperature up to 450 K. The maximum burning velocity has been obtained at equivalence ratio 1.1 for all the mixture conditions. The LBV results at atmospheric condition for n-butane-hydrogen-air mixture were obtained by extrapolating the experimental data at elevated temperatures. “Heat flux method” experimental setup was used for measuring the LBV of n-butane-hydrogen-air mixture at atmospheric condition. The results obtained for LBV at atmospheric conditions with the two different methods at 0%, 20%, 40% and 60% H 2 composition in n-butane were found to be in good agreement. The experimental results of LBV for n-butane were compared with the numerical predictions using USC mech II, Aramco mech 2.0 and LLNL reaction mechanisms. The numerical predictions of LBV using Aramco mech 2.0 shows good agreement with experimental data at rich, lean and stoichiometric mixture conditions.

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2018

B. Aravind, Raghuram, G. K. S., Dr. Ratna Kishore V., and Kumar, S., “Compact Design of Planar Stepped Micro Combustor for Portable Thermoelectric Power Generation”, Energy Conversion and Management, vol. 156, pp. 224-234, 2018.[Abstract]

An efficient prototype of a micro power generator with integrated micro combustor has been developed in the present study. The proposed design of the integrated micro-combustor provides high surface temperature with superior temperature uniformity and enhanced flame stability limits, a prerequisite for a thermoelectric power generation system. This novel micro combustor configuration consists of three backward facing steps with a recirculation hole fabricated in a rectangular heating medium of aluminium material. Parametric studies are carried out by varying the mixture inlet velocity, equivalence ratio and coolant flow rate to obtain the optimized operating conditions for maximum power generation. Two thermoelectric modules are mounted on the system operating with liquefied petroleum gas as fuel. A maximum conversion efficiency of 3.3% is obtained at ϕ = 0.95 with a mixture velocity of 7.5 m/s and a load resistance of 4 Ω across the thermoelectric generator. The effect of porous media is investigated to enhance the flame stability limits in the micro combustor. Porous media significantly enhances the upper flame stability limits and maximum conversion efficiencies (3.8%, 4.03%, and 3.73% at ϕ = 1, 0.9 and 0.8 at 10 m/s). A significantly higher power density (∼50% higher than existing systems) of 0.12 mW/mm3 of system volume is achieved. A compact design of the prototype system with high conversion efficiency shows the possibility of its application for various systems requiring portable power for remote, stand-alone, military and aerospace applications. © 2017 Elsevier Ltd

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2018

R. Sankarasubramanian, Sridhar, A., Prashanth, M. S., Mohammad, A., Dr. Ratna Kishore V., and Dr. Laxman Vaitla, “Influence of Thickness on Performance Characteristics of Non-sinusoidal Plunging Motion of Symmetric Airfoil”, Aerospace Science and Technology, vol. 81, pp. 333-347, 2018.[Abstract]

For the past few decades flapping wing aerodynamics has attracted a great deal of research interest from both the aeronautical and biological communities pertaining to the development of MAVs. The objective of this study is to examine and understand the effect of non-dimensional plunge amplitude and reduced frequency on propulsive performance of NACA 4-digit airfoil series and to examine the performance characteristics of square plunge motion and trapezoidal plunge motion. Two dimensional flow simulations around plunging symmetric aerofoils were performed using FLUENT. The simulations were carried out at Reynolds number of 20000 using incompressible laminar, NS solver. The reduced frequency (k) was varied from 0.5–5 and the plunging amplitude (h) was varied from 0.25–1.5. The plunging motions to the aerofoils were provided through UDFs. The effect of variation of k and h on the thrust coefficient (CT), power-input coefficient (CP) and propulsive efficiency (η) is studied. CT value is maximum for square plunge profile for all the airfoils. However, for a given value of h, with the increase in k, CT increases with increasing thickness of the airfoil and reaches a maximum value for airfoil thickness of NACA0018 and then starts decreasing. With varying h and k, it was observed that the propulsive efficiency reached a peak value and the peak shifts to higher h and k with increasing airfoil thickness. From the above study, it was concluded that airfoil thickness played a major part in influencing the thrust generation at low Strouhal number. However, at high Strouhal numbers airfoils showed diverse trends with respect to thrust generation. Sinusoidal plunging motion was more efficient but generated less thrust when compared to square and trapezoidal plunging motions.

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2018

A. A. Konnov, Mohammad, A., Dr. Ratna Kishore V., Kim, N. I., Prathap, C., and Kumar, S., “A comprehensive review of measurements and data analysis of laminar burning velocities for various fuel+air mixtures”, Progress in Energy and Combustion Science, vol. 68, pp. 197-267, 2018.[Abstract]

Accurate measurement and prediction of laminar burning velocity is important for characterization of premixed combustion properties of a fuel, development and validation of new kinetic models, and calibration of turbulent combustion models. Understanding the variation of laminar burning velocity with thermodynamic conditions is important from the perspective of practical applications in industrial furnaces, gas turbine combustors and rocket engines as operating temperatures and pressures are significantly higher than ambient conditions. With this perspective, a brief review of spherical flame propagation method, counterflow/stagnation burner method, heat-flux method, annular stepwise method, externally heated diverging channel method, and Bunsen method is presented. A direct comparison of power exponents for temperature (α) and pressure (β) obtained from different experiments and derived from various kinetic mechanisms is reported to provide an independent tool for detailed validation of kinetic schemes. Accurate prediction of laminar burning velocities at higher temperatures and pressures for individual fuels will help in closer scrutiny of the existing experimental data for various uncertainties due to inherent challenges in individual measurement techniques. Laminar burning velocity data for hydrogen (H2), gaseous alkane fuels (methane, ethane, propane, n-butane, n-pentane), liquid alkane fuels (n-heptane, isooctane, n-decane), alcohols (CH3OH, C2H5OH, n-propanol, n-butanol, n-pentanol) and di-methyl ether (DME) are obtained from literature of last three decades for a wide range of pressures (1–10 bar), temperatures (300–700 K), equivalence ratios and mixture dilutions. The available experimental and numerical data for H2 and methane fuels compares well for various pressures and temperatures. However, more experimental and kinetic model development studies are required for other fuels. Comparison of laminar burning velocity data obtained from different measurement techniques at higher initial pressures and temperatures showed significant deviations for all fuels. This suggests to conduct focused measurements at elevated pressure and temperature conditions for different fuels to enable the development of accurate kinetic models for wider range of mixtures and thermodynamic conditions. © 2018 Elsevier Ltd

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2018

G. Srikumar, Srikrishnan, V. A., Purushothaman, R. K., Thiagarajan, V., Dr. Ratna Kishore V., and Dr. Laxman Vaitla, “Numeri cal Study on Thrust Generation in an Airfoil Undergoing Nonsinusoidal Plunging Motion”, Journal of Aerospace Engineering, vol. 31, no. 4, pp. 787-796, 2018.[Abstract]

For the last few decades, an extensive research has been focused on flapping-wing aerodynamics to understand the generation of thrust due to pitching and plunging motions of an airfoil. However, most of the research emphasized an airfoil undergoing simple harmonic motion in either pitching or plunging motion. In this paper, a numerical study has been performed to estimate the thrust generated from a NACA0012 airfoil undergoing a periodic motion. The prescribed motion is created by an expression for harmonic and nonharmonic but periodic motions. The effects of these prescribed motions on thrust generation have been studied numerically for a Reynolds number of 20,000. It is observed that the thrust generated by the square and trapezoidal (periodic) plunging motions is much higher than the sinusoidal (harmonic) plunging motion. The effects of reduced frequency and amplitude of oscillations on the generation of thrust have also been studied. At higher reduced frequency and amplitudes, trapezoidal plunging motion generates higher thrust.

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2018

V. Venkatesh, Sriraam J., Bala Vignesh D., K., S., Dr. Ratna Kishore V., Dr. Srikrishnan A. R., Dr. Balajee Ramakrishnananda, and Suresh Batchu, “Studies on Effusion Cooling: Impact of Geometric Parameters on Cooling Effectiveness and Coolant Consumption”, Aerospace Science and Technology, vol. 77, pp. 58 - 66, 2018.[Abstract]

This study is focused on the impact of certain important geometric parameters on cooling effectiveness and coolant consumption for effusion cooling of aircraft combustor liner. The three dimensional turbulent flow field in a domain representing the combustor with several rows of effusion coolant injection is considered for the analysis. The geometric parameters considered are: angle of injection of the coolant, axial and transverse pitch of the injection holes, hole spacing and hole diameter. Also, based on the analysis of the temperature field within the chamber, a novel concept of ‘variable hole diameter’ has been introduced to reduce coolant consumption. A symmetric 3D computational model including the combustion chamber, coolant chamber and the effusion plate was used for the study. Conjugate heat transfer was modeled between the effusion-cooled wall and the two chambers. A detailed mass flow rate analysis has been performed for the various cases in order to study the impact of parameters on coolant consumption. The proposed approach of using an effusion plate with variable hole diameters is found to be effective in reducing the net coolant consumption significantly while maintaining a given level of cooling effectiveness.

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2018

A. N. Mohammed, Jithin, E. V., Dineshkumar, L., Dr. Ratna Kishore V., and Mohammad, A., “Tip Opening of Burner-Stabilized Flames”, Energy and Fuels, vol. 32, pp. 2344-2354, 2018.[Abstract]

The tip-opening mechanism of burner-stabilized flames is investigated computationally using premixed propane + air mixtures. The temperature, net production rate, and reaction rates are investigated for rich mixtures. The flame tip structure was analyzed on the basis of reaction rates to understand the conditions of the equivalence ratio at which the tip-opening phenomenon occurs. Numerical predictions of tip opening are in good agreement with experimental observations. The study revealed that the tip-opening phenomenon starts at φ = 1.4. As the mixture becomes rich, the tip opening was found to increase. When the flame tip opens, the volumetric heat release rate at the tip was found to be less than 50% of the heat release rate at the flame shoulder. An increase in the flame tip thickness was observed around 30% from equivalence ratios of 1.3-1.4. The effect of the temperature on the propane burner flame structure is studied by performing simulations at three different mixture inlet temperatures of 300, 350, and 400 K. When the temperature of the unburnt gas mixture increases, the propane-air tube burner flame tip opening begins at more fuel-rich conditions compared to that of the mixture at ambient temperature. A detailed sensitivity analysis was carried out to identify the reactions having large sensitivities. © 2018 American Chemical Society.

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2018

E. J. Veetil, Aravind, B., Mohammad, A., Kumar, S., and Dr. Ratna Kishore V., “Effect of Hole Pattern on the Structure of Small Scale Perorated Plate Burner Flames”, Fuel, vol. 216, pp. 722-733, 2018.[Abstract]

A numerical study on the structure of the laminar premixed flames established on perforated plate burners is performed. Three dimensional numerical simulations are performed on different perforated plate geometries, under various operating conditions, using methane reaction mechanism consisting 36 species and 253 reactions. The comparison of numerical results of inline and staggered configurations of perforated plate burner models show that the flame interaction has significant role in the structure and stabilization of perforated burner flame. The flame structure, flame height and the standoff distances are studied for both inline and staggered configurations at fuel lean and rich conditions. The flame standoff distance and the flame height found to be higher for staggered configuration in comparison to the inline configuration. The flame structure is studied for different hole-to-hole distances. The numerical results show an increase in flame base curvature with an increase in hole-to-hole distance for both inline and staggered configurations. The flame thickness reduces with an increase in hole-to-hole distance for both inline and staggered cases. The effect of recirculation and flame base curvature causes the flame base to get stabilized at a higher distance in staggered configuration in comparison to the inline configuration. © 2017 Elsevier Ltd

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2017

D. K. Valappil, Somasekharan, N., Krishna, S., Dr. Laxman Vaitla, and Dr. Ratna Kishore V., “Influence of solidity and wind shear on the performance of VAWT using a free vortex model”, International Journal of Renewable Energy Research, vol. 7, pp. 787-796, 2017.[Abstract]

Performance analysis of a VAWT and HAWT is highly complex due to fluid structure interactions and blade vortex interactions. However, there are simplified methods such as momentum theory to most expensive CFD models available for performance prediction. CACTUS is neither as simple as the momentum theory nor as complex as the CFD models, it is an open source code that uses the free vortex method to predict the performance of a wind turbine. In this paper, the effect of solidity and wind shear on the performance of an H-type Darrius VAWT is studied using CACTUS. Variation of solidity was achieved by changing the chord length (c/R =0.04-0.07) and number of blades (N =2,3). It has been observed that at lower tip speed ratio (TSR &lt; 3) the turbine with longer c/R was found to be more efficient due to large wind interception by the blades; and at higher TSR ( &gt; 3) shorter c/R was more efficient due to relatively low wake blade interaction. The improvement in performance due increasing the number of blades is effective only up to a particular TSR. Effect of wind shear due to the tower height from the ground using the power law equation with values of power law coefficient ranging from 0.1 to 0.3 has also been studied. It is observed that the power coefficients of the VAWT under a turbulent boundary layer are in congruence with the experimental results.

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2017

A. Subramanian, S. Yogesh, A., Sivanandan, H., Giri, A., Vasudevan, M., Vivek Mugundhan, and Dr. Ratna Kishore V., “Effect of airfoil and solidity on performance of small scale vertical axis wind turbine using three dimensional CFD model”, Energy, vol. 133, pp. 179-190, 2017.[Abstract]

This paper presents a study on the effect of solidity and airfoil profile on the performance of Vertical Axis Wind Turbines (VAWTs). A 1.1&nbsp;kW commercially viable Darrieus VAWT was studied using ANSYS Fluent. Four different airfoils – NACA 0012, NACA 0015, NACA 0030 and AIR 001 – were considered in the analysis. The tip speed ratios (λ) were varied from 1 to 2.5 with an incoming wind velocity of 10&nbsp;m/s. It was observed that NACA 0030 performed better at lower values of λ due to long duration of attached flow; while NACA 0012 performed better at λ&nbsp;&gt;&nbsp;1.8 with a wider range of λ. The shed vortex dissipates much faster for thinner airfoils than for thicker airfoils at higher values of λ. Two bladed VAWTs generated more power than the three bladed turbines. This indicated that turbines with lower solidity perform better at high λ.

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2017

A. N. Mohammed, Juhany, K. A., Kumar, S., Dr. Ratna Kishore V., and Mohammad, A., “Effects of CO2/N2 dilution on laminar burning velocity of stoichiometric DME-air mixture at elevated temperatures”, Journal of Hazardous Materials, vol. 333, pp. 215-221, 2017.[Abstract]

The laminar burning velocity of CO2/N2 diluted stoichiometric dimethyl ether (DME) air mixtures is determined experimentally at atmospheric pressure and elevated mixture temperatures using a mesoscale high aspect-ratio diverging channel with inlet dimensions of 25&nbsp;mm&nbsp;×&nbsp;2&nbsp;mm. In this method, planar flames at different initial temperatures (Tu) were stabilized inside the channel using an external electric heater. The magnitude of burning velocities was acquired by measuring the flame position and initial temperature. The mass conservation of the mixture entering the inlet and the stationary planar flame front is applied to obtain the laminar burning velocity. Laminar burning velocity at different initial mixture temperatures is plotted with temperature ratio (Tu/Tu,o), where a reference temperature (Tu,o) of 300&nbsp;K is used. Enhancement in the laminar burning velocity is observed with mixture temperature for DME-air mixtures with CO2 and N2 dilutions. A significant decrease in the burning velocity and slight increase in temperature exponent of the stoichiometric DME-air mixture was observed with dilution at same temperatures. The addition of CO2 has profound influence when compared to N2 addition on both burning velocity and temperature exponent. © 2017 Elsevier B.V.

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2017

A. Pa Singh, Dr. Ratna Kishore V., Yoon, Yc, Minaev, Sd, and Kumar, Sa, “Effect of Wall Thermal Boundary Conditions on Flame Dynamics of CH4-Air and H2-Air Mixtures in Straight Microtubes”, Combustion Science and Technology, vol. 189, no. 1, pp. 150-168, 2017.[Abstract]

Unsteady numerical simulations with detailed chemistry have been carried out for premixed stoichiometric CH4-air and H2-air mixtures in straight microtubes to understand the flame-wall coupling and its effect on flame dynamics for a range of wall heat transfer conditions. Varying flame shapes were observed during the unsteady flame propagation mode. These flame modes are represented with flame shape angles and the corresponding flame shape is correlated to the wall heat transfer conditions. Various similarities in flame propagation characteristics have been observed for both of the fuels. A normalization technique has been adopted to establish the independence of variation of nondimensional flame propagation velocity on fuel type. It has been observed that an increase in convective heat transfer coefficient, h, though increasing the heat loss from a propagating flame, does not necessarily lead to a monotonic decrease in flame propagation speed. A transition regime where propagating flame changes its shape has been identified. The variation of mass flux in the vicinity of the propagating flame has been used to gain better understanding of flow redirection and its impact on flame shape and flame propagation behavior. © 2017 Taylor &amp; Francis.

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2017

Dr. Ratna Kishore V., Minaev, Sb, Akram, Mc, and Kumar, Sd, “Dynamics of premixed methane/air mixtures in a heated microchannel with different wall temperature gradients”, RSC Advances, vol. 7, pp. 2066-2073, 2017.[Abstract]

The observation of various flame propagation modes for externally heated tubes has led to many fundamental studies aimed at understanding flame propagation in microtubes. During these studies, it has been observed that for moderately low flow velocities, flames with repetitive extinction and ignition (FREI) have been observed to exist in various experimental, theoretical and numerical studies. The formation of these FREI flame modes depends on various parameters such as channel dimensions, wall temperature gradient, flow rates and mixture type. In the present work, an effort has been made to understand the effect of the wall temperature gradient on the FREI phenomenon through a 1 mm diameter circular tube using 2D numerical studies with detailed GRI Mech3.0 for premixed methane/air mixtures. The different wall temperature gradients analyzed are varied from 33.3-1 K mm−1, with an upper range corresponding to experimental conditions. Five different phases of flame propagation have been observed during the FREI flame propagation mode. The entire fuel gets consumed during the cycle and a significant amount of unburned CO remains during the weak reaction phase, towards the extinction of FREI mode. The effect of the wall temperature gradient on the FREI ignition phenomenon has been investigated to understand the development of ignition kernels. It is observed that the ignition happens at the axis and not at the wall of the channel. This happens due to a boundary-layer phenomenon discouraging ignition at the wall. It has been observed that a decrease in the temperature gradient results in movement of the ignition point towards the low-temperature region. The peak CO value increases with a decrease in the wall temperature gradient. © The Royal Society of Chemistry.

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2016

B. Aravind, Dr. Ratna Kishore V., Singh, A. P., Yoon, Y., Minaev, S., and Kumar, S., “Investigations on flame dynamics of premixed H 2–air mixtures in microscale tubes”, RSC advances, vol. 6, no. 55, pp. 50358–50367, 2016.

2016

V. Hariharan, Dr. Ratna Kishore V., and Prathap, C., “Investigation on supersonic combustion of hydrogen with variation of combustor inlet conditions”, International Journal of Hydrogen Energy, vol. 41, pp. 5833 - 5841, 2016.[Abstract]

The present work numerically investigated the effect of variation in the inlet Mach number and stagnation temperature on the mixing of fuel with the oxidizer and the subsequent stabilization of a flame in a combustor at supersonic conditions. Dimensions of the studied combustor were taken from literature. It had a 10° wedge located at the top wall of the combustor. The combustor was modeled and analyzed using ANSYS FLUENT software. Three-dimensional, compressible, reacting flow calculations with a detailed chemistry model were performed. Turbulence was modeled using SST k-ω model. Necessary grid refinement was done to capture the incident oblique shock formed at the 10° wedge. Hydrogen was injected through the fuel inlet port. The computations were performed for Mach numbers of 2.0, 2.5 and 3.0&nbsp;at the combustor inlet for a combustion inlet stagnation temperature of 1500&nbsp;K. Later, the combustor inlet Mach number was kept constant at 2.5 and the combustor inlet stagnation temperature was varied as follows: 1500&nbsp;K, 1700&nbsp;K, and 1900&nbsp;K. The results indicated that as the combustor inlet Mach number increased, the location of incidence of the oblique shock shifted to the downstream of the fuel inlet and it resulted in the better mixing of the fuel with cross flow stream of air and led to better degree of combustion of hydrogen. The contours of mole fraction of OH radical and hydrogen also corroborated the improvement in the mixing of fuel with the cross flow air and the subsequent flame stabilization at higher Mach numbers. The flow pattern, mixing of fuel with air and flame stabilization was not affected significantly till 1700&nbsp;K whereas for 1900&nbsp;K, combustion of hydrogen was more uniform.

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2016

E. J. Veetil, Rajith, C. V., and Dr. Ratna Kishore V., “Numerical simulations of steady perforated-plate stabilized Syngas air pre-mixed flames”, International Journal of Hydrogen Energy, vol. 41, no. 31, pp. 13747-13757, 2016.[Abstract]

Numerical investigations of steady, laminar premixed Syngas-air flames are presented in this paper. Three-dimensional simulations were performed to examine the impact of operating conditions on steady state characteristics of perforated burner flame. A detailed H2 CO reaction mechanism having 12 species and 38 reactions was used for combustion modelling. The three dimensional simulation results are validated against the 1D flat flame result using PREMIX. Effects of inlet velocity, fuel composition and equivalence ratio on flame stability were examined. A clearly identified recirculation zone was present above the top surface of the burner plate in the case of 50% H2-50% CO Syngas mixture. The strength recirculation zone was diminishing with the increase in percentage of hydrogen in the Syngas mixture, and the flame has stabilized closer to the top surface of the burner plate. The flame stand-off distance is found to decrease with increase in inlet velocity. Effect of increase in H2 fraction in Syngas has less effect on flame height at higher H2 fractions. More »»

2016

B. M. M. S. R. S, Dr. Ratna Kishore V., P, A. S., and Balaji K., “Power generation by high head water in a building using micro hydro turbine-a greener approach.”, Environ Sci Pollut Res Int, vol. 23, no. 10, pp. 9381-90, 2016.[Abstract]

Demand for green energy production is arising all over the world. A lot of emphasis is laid in making the buildings green. Even a small amount of energy savings made contribute to saving the environment. In this study, an idea is proposed and studied to extract power from the high head water in the pipelines of a building. A building of height 15 m is considered for this study. Water flowing in the pipe has sufficient energy to run a micro hydro turbine. The feasibility of producing electrical energy from the energy of pipe water is found. The motivation is to find the feasibility of generating power using a low-cost turbine. The experimental setup consists of micro turbine of 135 mm diameter coupled to a 12-V DC generator; LEDs and resistors are employed to validate the results. The theoretical calculations were presented using the fundamental equations of fluid mechanics. The theoretical results are validated using experimental and numerical results using CFD simulation. In addition, exergy analysis has been carried out to quantify the irreversibilities during the process in the system.

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2016

Ba Aravind, Dr. Ratna Kishore V., Singh, A. Pa, Yoon, Yc, Minaev, Sd, and Kumar, Sa, “Investigations on flame dynamics of premixed H2-air mixtures in microscale tubes”, RSC Advances, vol. 6, no. 55, pp. 50358-50367, 2016.[Abstract]

Detailed numerical studies through unsteady simulations with detailed hydrogen chemistry have been reported for premixed H2-air flames in straight microtubes to understand the role of flame-wall coupling and its effect on flame dynamics for a range of wall heat transfer conditions. Depending on the wall heat transfer conditions, and tube diameters, varying flame shapes were observed. These flame modes are represented with flame shape angles and corresponding flame shape is correlated to wall heat transfer conditions. It has been observed that an increase in wall heat transfer coefficient, h, though it increases the heat loss from a propagating flame, does not necessarily lead to a monotonic decrease in flame propagation speed. A transition regime, where the propagating flame changes its shape, has been identified. The variation of mass flux in the vicinity of the propagating flame has been used to gain a better understanding of flow-redirection and its impact on flame shape and flame propagation speed for premixed H2-air mixtures. © 2016 The Royal Society of Chemistry. More »»

2016

A. Tummala, Dr. Ratna Kishore V., Sinha, D. Kumar, Indraja, V., and V. Krishna, H., “A review on small scale wind turbines”, Renewable and Sustainable Energy Reviews, vol. 56, pp. 1351 - 1371, 2016.[Abstract]

Abstract Meeting future world energy needs while addressing climatic changes has led to greater strain on conventional power sources. One of the viable sustainable energy sources is wind. But the installation large scale wind farms has a potential impact on the climatic conditions, hence a decentralized small scale wind turbines is a sustainable option. This paper presents review of on different types of small scale wind turbines i.e., horizontal axis and vertical axis wind turbines. The performance, blade design, control and manufacturing of horizontal axis wind turbines were reviewed. Vertical axis wind turbines were categorized based on experimental and numerical studies. Also, the positioning of wind turbines and aero-acoustic aspects were presented. Additionally, lessons learnt from various studies/countries on actual installation of small wind turbines were presented. More »»

2016

A. Nair, Dr. Ratna Kishore V., and Kumar, S., “Effect OF CO2/N2 dilution on laminar burning velocity of liquid petroleum gas-air mixtures at elevated temperatures”, Energy, vol. 100, pp. 145-153, 2016.[Abstract]

The present experimental study reports the effect of CO2/N2 dilution on laminar burning velocity of premixed LPG (liquid-petroleum-gas)-air mixtures at elevated temperatures using a preheated mesoscale diverging channel technique. The experiments were carried out for a range of equivalence ratios varying from 0.8 < Φ < 1.3 with percentage dilution of the fuel component by volume (β) for CO2 varying from 10% < β < 30% and N2 varying from 10% < β < 40%. A power-law correlation has been obtained for the present experimental data as a function of percentage dilution, mixture temperature and equivalence ratio. It has been observed that an increase in dilution with CO2/N2 leads to an increase in temperature exponent (α). The increase in temperature exponent due to CO2 dilution is more pronounced as compared to N2 dilution case. A flame structure study has been carried out to understand the effect of mixture temperature and diluent using USC (University of Southern California) Mech II reaction mechanism. © 2016 Elsevier Ltd. More »»

2015

A. R. Sudhamshu, Pandey, M. Chandra, Sunil, N., Satish, N. S., Vivek Mugundhan, and Dr. Ratna Kishore V., “Numerical study of effect of pitch angle on performance characteristics of a HAWT”, Engineering Science and Technology, an International Journal, vol. 19, no. 1, pp. 632–641, 2015.[Abstract]

Wind energy is one of the clean renewable forms of energy that can handle the existing global fossil fuel crisis. Although it contributes to 2.5% of the global electricity demand, with diminishing fossil fuel sources, it is important that wind energy is harnessed to a greater extent to meet the energy crisis and problem of pollution. The present work involves study of effect of pitch angle on the performance of a horizontal axis wind turbine (HAWT), NREL Phase VI. The wind velocities considered for the study are 7, 15.1 and 25.1 m/s. The simulations are performed using a commercial CFD code Fluent. A frozen rotor model is used for simulation, wherein the governing equations are solved in the moving frame of reference rotating with the rotor speed. The SST k-ω turbulence model has been used. It is seen that the thrust increases with increase in wind velocity, and decreases with increase in pitch angle. For a given wind velocity, there is an optimum pitch angle where the power generated by the turbine is maximum. The observed effect of pitch angle on the power produced has been correlated to the stall characteristics of the airfoil blade

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2015

A. Gowrishankar, Vignesh, S., Sunder, P. B. Shyam, Abhinav, R., Vivek Mugundhan, and Dr. Ratna Kishore V., “Numerical Study of Natural Convection in an Enclosure with an Internal Heat Source at Higher Rayleigh Numbers”, Heat Transfer - Asian Research, vol. 44, pp. 620-640, 2015.[Abstract]

Natural convection is extensively used in cooling of large scale electrical and electronic equipments. This work involves study of flow and heat transfer characteristics in enclosures with partial openings having an internal heat source at higher Rayleigh number (Rah > 106). It involves the numerical simulation of 2D steady state natural convection in enclosures of different aspect ratios (H/W = 2 and 3) for five Rayleigh numbers (Rah = 107, 108, 109, 1010, and 1011). Two different configurations have been considered based on the number and position of vents-diagonal side (DS) and two inlets one outlet (2I1O). The time dependent nature of the flow is characterized by performing a Fast Fourier Transform (FFT) analysis of temperature and velocity at a characteristic location in the enclosure. The global parameters considered are the mass flow rate driven through the cavity by the heater and the average Nu defined over the heater surface. It is seen that with increase in Rah, flow becomes more fluctuating and moves towards chaotic regime and this transition is quicker at lower H/W. For the given configuration both the global parameters increases with increase in Rah and decrease in H/W. © 2015 Wiley Periodicals, Inc.

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2015

B. Aravind, Dr. Ratna Kishore V., and Mohammad, A., “Combustion characteristics of the effect of hydrogen addition on LPG–air mixtures”, International Journal of Hydrogen Energy, vol. 40, no. 46, pp. 16605 - 16617, 2015.[Abstract]

The present study reports the effect of hydrogen addition on combustion characteristics of LPG–air mixtures for different mixture compositions, temperatures and pressures. Numerical simulation has been carried out using USC Mech II reaction mechanism, consisting of 111 species and 784 reactions. It is found that, variation of the flame speeds were relatively small for various compositions of LPG–air mixtures used. Thus 50% propane – 50% butane mixture is considered for the present work. The effect of volumetric H2 addition on laminar flame speed and ignition delay of selected LPG (50% propane&nbsp;+&nbsp;50% butane) air mixtures is then studied for hydrogen addition ratio varying from 0&nbsp;&lt;&nbsp;RH&nbsp;&lt;&nbsp;0.5 and over a wide range of mixture equivalence ratio. Also, the investigation is carried out for mixture temperature up to 450&nbsp;K and pressure ranging from 1 to 10&nbsp;bar. A parabolic variation of laminar flame speed is observed with equivalence ratios giving peak value for slightly rich mixture. A linear correlation has been observed for the flame speed as a function of hydrogen addition, RH at all the conditions studied. Whereas, power law correlation has been proposed for the hydrogen added LPG–air mixture, to understand the dependency of laminar flame speed on temperature and pressure. A generic correlation has been proposed to study the combined effect of temperature and pressure on laminar flame speed.

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2015

S. A.P., Dr. Ratna Kishore V., S., M., and S., K., “Numerical investigations of unsteady flame propagation in stepped microtubes”, RSC Advances, vol. 5, no. 122, pp. 100879-100890, 2015.[Abstract]

Transient numerical simulations with detailed chemistry have been carried out for premixed stoichiometric CH4-air and H2-air flames in two-dimensional stepped microtubes for a range of wall heat transfer conditions. Investigations on such configurations are important from the perspective of the design of micro combustion devices, flame arresters and safety in domestic and industrial combustion devices. Similarities in flame propagation characteristics have been brought out through a detailed analysis for both the fuels. Detailed analysis of the propagating flame near the channel step revealed an interesting phenomenon of sudden increase in flame propagation velocities for a certain range of wall heat transfer coefficient, h. A quantitative value of ratio of heat-loss to heat-generation at the contraction has been proposed which helps predict the flame propagation through sudden channel steps. © The Royal Society of Chemistry 2015.

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2015

Aa Nair, Dr. Ratna Kishore V., and Kumar, Sb, “Dynamics of Premixed Hydrogen-Air Flames in Microchannels with a Wall Temperature Gradient”, Combustion Science and Technology, vol. 187, no. 10, pp. 1620-1637, 2015.[Abstract]

Two-dimensional numerical investigations on flame dynamics in a microchannel have been carried out for premixed hydrogen-air mixtures with detailed chemistry. Detailed studies on the formation of flames with repetitive extinction and ignition (FREI) mode have been carried out for a 0.75-mm diameter tube with fixed conditions of flow velocity of 10 cm/s and Φ = 0.5-1.0 with wall temperature linearly varying from 300 K to 960 K. An unsteady flame propagation behavior similar to FREI has been observed to appear for a range of mixture equivalence ratios and channel diameters. FREI was observed to occur for 0.5 &lt; 0.8 for 0.75-mm diameter channel and disappears for higher mixture equivalence ratios. The effect of tube diameter has also been analyzed for 10 cm/s inlet velocity of mixture at 300-1050 K wall temperature for diameters of 0.6 mm, 0.75 mm, and 1.0 mm. As the tube diameter increased, the frequency of the FREI process decreased, which hints to the contribution of disappearance of FREI phenomenon. © Taylor &amp; Francis Group, LLC.

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2015

Dr. Ratna Kishore V., Arun, J., Dr. Padmanaban R., and V, B., “Parametric studies of dissimilar friction stir welding using computational fluid dynamics simulation”, International Journal of Advanced Manufacturing Technology, vol. 80, pp. 91-98, 2015.[Abstract]

A two-dimensional steady state visco-plastic model has been developed for friction stir welding of dissimilar metals using a commercial CFD code, FLUENT®. Volume of Fluid (VOF) approach is used to model the welding process of dissimilar metals. Initially, the model developed is validated against experimental measurements of Peel et al. (Metall Mater Trans A 37 A:2183–2193, 2006). Simulations were done for two different material combinations, AA 5083–AA 6061 and AA 2024–AA 7075. The temperature distribution and material flow around the tool is studied for different position of materials, process parameters, and tool profiles. It is seen that the peak temperature is generated on harder material side with change in position of materials. This is mainly because on harder material side more heat is generated due to viscous dissipation. The trivex pin profile is found to be better than circular pin profile by reducing welding traverse force and an efficient symmetric mixing of materials. © 2015, Springer-Verlag London.

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2015

Dr. Ratna Kishore V., Vivek Mugundhan, Goutham, K., Sreekanth, G. R., Dharmarajan, S., and Goel, M., “Numerical study of a buoyant plume from a multi-flue stack into a variable temperature gradient atmosphere”, Environmental Science and Pollution Research, vol. 22, pp. 16814–16829, 2015.[Abstract]

Air pollution is one of the major global hazards and industries have been one of its major contributors. This paper primarily focuses on analyzing the dispersion characteristics of buoyant plumes of the pollutant released from a multi-flue vertical stack into a variable temperature gradient atmosphere (α) in a constant-velocity cross wind using two stack configurations—inline and parallel. The study is conducted for different Froude numbers, Fr = 12.64, 9.55, and 8.27. The atmospheric temperature gradients considered for the study are 0, +1, +1.5, and +2 K/100 m. The numerical study is done using the commercial computational fluid dynamics (CFD) code FLUENT. The effects of stack configuration, α, and Fr on the plume characteristics are presented. It is observed that the plume rises higher and disperses over a larger area with the inline configuration due to better mixing and shielding effect. With higher α, it is seen that the plume rises initially and then descends due to variation of the buoyant force. The plume rise initially is strongly influenced by the momentum of the jet, and as it moves downstream, it is influenced by the cooling rate of the plume. Furthermore, the plume rises higher and disperses over a larger area with a decrease in Fr.

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2014

S. Chandramouli, Premsai, T. P., Prithviraj, P., Mugundhan, V., and Dr. Ratna Kishore V., “Numerical analysis of effect of pitch angle on a small scale vertical axis wind turbine”, International Journal of Renewable Energy Research (IJRER), vol. 4, pp. 929–935, 2014.[Abstract]

The current work involves a numerical study of the effect of preset pitch angle on the performance of a Vertical Axis Wind Turbine (VAWT). A three bladed H-Darrieus VAWT has been considered for the study. The equations governing the flow are solved using a commercial CFD code ANSYS CFX 13. The turbine with NACA 0015 profile and zero pitch angle as the reference case for comparison. The analysis has been done for three pitch angles -6o, 0o, +6o, tip speed ratios (TSR) from 1 to 2.2 and wind velocities of 6, 8 and 10 m/s. Of the pitch angle considered, the best performance is observed with -6o for all tip speed ratios and wind velocities. This has been explained by studying the instantaneous torque characteristics of the turbine. It is seen that at any given instant, the blade in the upwind region contributes significantly to the positive torque with other blades either contributing less or negating the positive torque. The pressure coefficient distributions over the upwind blade and stream lines at different azimuthal angles have also been analysed to understand the effect of pitch.

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2014

E. V. Jithin, Dr. Ratna Kishore V., and Varghese, R. J., “Three-dimensional simulations of steady perforated-plate stabilized propane-air premixed flames”, Energy and Fuels, vol. 28, no. 8, pp. 5415-5425, 2014.[Abstract]

A numerical investigation of steady laminar premixed propane-air flames is presented. A three-dimensional simulation has been performed to examine the impact of operating conditions on steady-state characteristics of a perforated burner flame. A numerical simulation has been carried out using a reduced propane-air reaction mechanism having 30 species and 192 reactions. The results are validated against the one-dimensional flat-flame result obtained using PREMIX. Effects of the equivalence ratio, inlet velocity, hole-hole distance, and plate thermal conductivity on flame stability are examined. The flame stand-off distance increases with the increase in the inlet velocity. As the equivalence ratio increases, the heat flux to the plate increases as the flame moves closer to the plate. When the plate is adiabatic, the conical flame rests on the plate. The flame stand-off distance increases as the plate thermal conductivity is increased. The flame moves downstream of the plate as the distance between the adjacent holes is increased. © 2014 American Chemical Society.

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2013

M. K. Lalith, Dinesh, A., Unnikrishnan, S., Radhakrishnan, A., Srihari S., and Dr. Ratna Kishore V., “Modeling of homogeneous mixture formation and combustion in GDI engine with negative valve overlap”, ISRN Mechanical Engineering, vol. 12, no. 1, 2013.[Abstract]

Mixture homogeneity plays a crucial role in HCCI engine. In the present study, the mixture homogeneity was analysed by three-dimensional engine model. Combustion was studied by zero-dimensional single zone model. The engine parameters studied include speed, injector location, valve lift, and mass of fuel injected. Valve lift and injector location had less impact on mixture formation and combustion phasing compared to other parameters. Engine speed had a noticeable effect on mixture homogeneity and combustion characteristics. © 2013 M. K. Lalith et al.

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2013

R. Abhinav, Sunder, P. B. S., Gowrishankar, A., Vignesh, S., Vivek, M., and Dr. Ratna Kishore V., “Numerical study on effect of vent locations on natural convection in an enclosure with an internal heat source”, International Communications in Heat and Mass Transfer, vol. 49, pp. 69-77, 2013.[Abstract]

Natural convection is a widely studied phenomenon because of the extensive applications in cooling of large scale electrical and electronic equipments. The current study involves study of effect of vent locations on natural convection in enclosures with partial openings having an internal heat source. It involves the numerical simulation of 2D steady state natural convection in enclosure of different aspect ratios (H/W=1, 2 and 3) for lower Rayleigh numbers (Rah=103, 104 and 105). Four different configurations have been considered based on the number and position of vents - same side (SS), diagonal side (DS), one inlet two outlets (1I2O) and two inlets one inlet (2I1O). The mass flow rate driven through the enclosure and the average Nusselt number over the heater surface for all the four configurations have been compared. It is found that the 2I1O configuration yielded better heat transfer rates of the four considered. It was found that the mass flow rates and Nu increased with increase in Rah and decrease in the aspect ratio. © 2013 Elsevier Ltd.

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2012

M. Akram, Dr. Ratna Kishore V., and Kumar, S., “Laminar Burning Velocity of Propane/CO2/N2–Air Mixtures at Elevated Temperatures”, Energy & Fuels, vol. 26, no. 9, pp. 5509-5518, 2012.[Abstract]

The laminar burning velocity of pure and diluted high-temperature propane–air mixtures is extracted from the planar flames stabilized in the preheated mesoscale diverging channel. The experiments were carried out for a range of equivalence ratios of 0.7 ≤ Φ ≤ 1.3 and mixture temperatures of 370–650 K. The effect of dilution using CO2 and N2 gases (up to 40%) on C3H8–air burning velocity is also studied. Experiments complimented with computational studies of experimental conditions confirm that the stabilized flames were planar in both transverse and depth directions, and the burning velocity with heat flux in the present case is nearly equal to the adiabatic burning velocity. The detailed uncertainty analysis shows the accuracy of the present measurement within ±5%. Computational predictions of burning velocity and detailed flame structure were performed using PREMIX code. The present experiments are successfully validated against existing experimental and computational results. The peak burning velocity was observed for slightly rich mixtures even at higher mixture temperatures. The minimum value of the temperature exponent is observed for slightly rich mixtures. The burning velocity was observed to decrease with the dilution of inert gases. The addition of CO2 shows a pronounced decrease in the burning velocity, as compared to N2.

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2012

Dr. Padmanaban R., Balusamy, Vb, and Dr. Ratna Kishore V., “Effect of axial pressure and tool rotation speed on temperature distribution during dissimilar friction stir welding”, Advanced Materials Research, vol. 418-420, pp. 1934-1938, 2012.[Abstract]

A computational fluid dynamics(CFD) based numerical model is developed to predict the temperature distribution during Friction Stir Welding(FSW) of dissimilar aluminum alloys. The effect of tool rotation speed and axial pressure on heat transfer during FSW has been studied. Numerical results indicate that the maximum temperature in FSW process can be increased with the increase of the axial pressure and tool rotation speed. The influence region of the tool shoulder in the direction of thickness can be increased with the increase in the axial pressure on the shoulder. © (2012) Trans Tech Publications, Switzerland

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2012

Ma Akram, Dr. Ratna Kishore V., and Kumar, Sa, “Laminar burning velocity of propane/CO 2/N 2-air mixtures at elevated temperatures”, Energy and Fuels, vol. 26, pp. 5509-5518, 2012.[Abstract]

The laminar burning velocity of pure and diluted high-temperature propane-air mixtures is extracted from the planar flames stabilized in the preheated mesoscale diverging channel. The experiments were carried out for a range of equivalence ratios of 0.7 ≥ Φ ≥ 1.3 and mixture temperatures of 370-650 K. The effect of dilution using CO 2 and N 2 gases (up to 40%) on C 3H 8-air burning velocity is also studied. Experiments complimented with computational studies of experimental conditions confirm that the stabilized flames were planar in both transverse and depth directions, and the burning velocity with heat flux in the present case is nearly equal to the adiabatic burning velocity. The detailed uncertainty analysis shows the accuracy of the present measurement within ±5%. Computational predictions of burning velocity and detailed flame structure were performed using PREMIX code. The present experiments are successfully validated against existing experimental and computational results. The peak burning velocity was observed for slightly rich mixtures even at higher mixture temperatures. The minimum value of the temperature exponent is observed for slightly rich mixtures. The burning velocity was observed to decrease with the dilution of inert gases. The addition of CO 2 shows a pronounced decrease in the burning velocity, as compared to N 2. © 2012 American Chemical Society.

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2011

Dr. Ratna Kishore V., Ravi, M. R., and Ray, A., “Adiabatic burning velocity and cellular flame characteristics of H 2–CO–CO 2–air mixtures”, Combustion and Flame, vol. 158, no. 11, pp. 2149–2164, 2011.[Abstract]

The objective of this work was to study the effect of dilution with carbon dioxide on the adiabatic burning velocity of syngas fuel (with various H2/CO ratios)-air(21% O2–79% N2 by volume) mixtures along with detailed understanding of cellular flame structures. Heat flux method with a setup similar to that of de Goey and co-workers [1] was used for measurement of burning velocities. Validation experiments were done for H2 (5%)–CO (95%)–air and H2 (5%)–CO (45%)–CO2 (50%)–air mixtures at various equivalence ratios and the results were in good agreement with published data in the literature. The mixtures considered in this work had 1:4, 1:1 and 4:1 H2/CO ratio in the fuel and 40%, 50% and 60% CO2 dilution. The burning velocity increased significantly with the increase in H2 content in mixture of H2–CO with fixed CO2 dilution. The burning velocity reduced remarkably with carbon dioxide dilution in H2–CO mixture due to reduction in heat release, flame temperature and thermal diffusivity of the mixture. The location of peak adiabatic burning velocity shifted from ϕ = 1.6 for 40% CO2 to ϕ = 1.2 for 60% CO2, whereas it remained unchanged with variation of H2:CO ratio (4:1, 1:1 and 1:4) at a given CO2 dilution. A comparison of experiments and simulations indicated that the Davis et al. [2] mechanism predicted burning velocities well for the most of experimental operating conditions except for rich conditions. For some lean mixtures, flames exhibited cellular structures. In order to explain the structures and generate profiles of various field variables of interest, computations of three dimensional porous burner stabilized cellular flames were performed using commercial CFD software FLUENT. Simulations for lean H2 (25%)–CO (25%)–CO2 (50%)–air mixtures (ϕ = 0.6 and 0.8) produced cellular flame structures very similar to those observed in the experiments. It was found that the in the core region of a typical cell, stretch rate was positive, the volumetric heat release rate was high and the net reaction rate for the reaction O + H2 ⇄ H + OH and the net consumption rate of H2 were both high.

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2009

P. Parthasarathy, Talukdar, P., and Dr. Ratna Kishore V., “Enhancement of heat transfer with porous/solid insert for laminar flow of a participating gas in a 3-D square duct”, Numerical Heat Transfer, Part A: Applications, vol. 56, pp. 764–784, 2009.[Abstract]

In recent years, porous or solid insert has been used in a duct for enhancing heat transfer in high temperature thermal equipment, where both convective and radiative heat transfer play a major role. In the present work, the study of heat transfer enhancement is carried out for flow through a square duct with a porous or a solid insert. Most of the analyses are carried out for a porous insert. The hydrodynamically developing flow field is solved using the Navier–Stokes equation and the Darcy–Brinkman model is considered for solving the flow in the porous region. The radiative heat transfer is included in the analysis by coupling the radiative transfer equation to the energy equation. The fluid considered is CO2 with temperature dependent thermophysical properties. Both the fluid and the porous medium are considered as gray participating medium. The increase in heat transfer is analyzed by comparing the bulk mean temperature, Nusselt number, and radiative heat flux for different porous size and orientation, Reyonlds number, and Darcy number.

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2009

Dr. Ratna Kishore V., Muchahary, R., Ray, A., and Ravi, M. R., “Adiabatic burning velocity of H 2–O 2 mixtures diluted with CO 2/N 2/Ar”, international journal of hydrogen energy, vol. 34, no. 19, pp. 8378–8388, 2009.[Abstract]

Global warming due to CO2 emissions has led to the projection of hydrogen as an important fuel for future. A lot of research has been going on to design combustion appliances for hydrogen as fuel. This has necessitated fundamental research on combustion characteristics of hydrogen fuel. In this work, a combination of experiments and computational simulations was employed to study the effects of diluents (CO2, N2, and Ar) on the laminar burning velocity of premixed hydrogen/oxygen flames using the heat flux method. The experiments were conducted to measure laminar burning velocity for a range of equivalence ratios at atmospheric pressure and temperature (300 K) with reactant mixtures containing varying concentrations of CO2, N2, and Ar as diluents. Measured burning velocities were compared with computed results obtained from one-dimensional laminar premixed flame code PREMIX with detailed chemical kinetics and good agreement was obtained. The effectiveness of diluents in reduction of laminar burning velocity for a given diluent concentration is in the increasing order of argon, nitrogen, carbon dioxide. This may be due to increased capabilities either to quench the reaction zone by increased specific heat or due to reduced transport rates. The lean and stoichiometric H2/O2/CO2 flames with 65% CO2 dilution exhibited cellular flame structures. Detailed three-dimensional simulation was performed to understand lean H2/O2/CO2 cellular flame structure and cell count from computed flame matched well with the experimental cellular flame.

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2008

Dr. Ratna Kishore V., Duhan, N., Ravi, M. R., and Ray, A., “Measurement of adiabatic burning velocity in natural gas-like mixtures”, Experimental Thermal and Fluid Science, vol. 33, pp. 10–16, 2008.[Abstract]

Experimental measurements of the adiabatic burning velocities were carried out for natural gas-like mixtures burning in air over a range of equivalence ratios at atmospheric pressure. Effect of CO2 dilution up to 60%, N2 dilution up to 40% and 25% enrichment of ethane on burning velocity of methane–air flames were studied. Heat flux method with setup similar to that of [K.J. Bosschaart, L.P.H. de Goey, Detailed analysis of the heat flux method for measuring burning velocity, Combustion and Flame 132 (2003) 170–180] was used for measurement of burning velocities. Initially experiments were done for methane–air and ethane–air mixtures at various equivalence ratios and the results were in good agreement with published data in the literature. Computations were performed using PREMIX code with GRI 3.0 reaction mechanism for all the mixtures. Predicted flame structures were used to the explain the effect of N2 and CO2 dilution on burning velocity of methane–air flames. Peak burning velocity for CH4/CO2–air mixtures occur near to ϕ = 1.0.

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2008

Dr. Ratna Kishore V., Ravi, M. R., and Ray, A., “Effect of hydrogen content and dilution on laminar burning velocity and stability characteristics of producer gas-air mixtures”, Journal of Combustion, vol. 2008, 2008.[Abstract]

Producer gas is one of the promising alternative fuels with typical constituents of H2, CO, CH4, N2, and CO2. The laminar burning velocity of producer gas was computed for a wide range of operating conditions. Flame stability due to preferential diffusional effects was also investigated. Computations were carried out for spherical outwardly propagating flames and planar flames. Different reaction mechanisms were assessed for the prediction of laminar burning velocities of CH4, H2, H2-CO, and CO-CH4 and results showed that the Warnatz reaction mechanism with C1 chemistry was the smallest among the tested mechanisms with reasonably accurate predictions for all fuels at 1 bar, 300 K. To study the effect of variation in the producer gas composition, each of the fuel constituents in ternary CH4-H2-CO mixtures was varied between 0 to 48%, while keeping diluents fixed at 10% CO2 and 42% N2 by volume. Peak burning velocity shifted from to 1.1 as the combined volumetric percentage of hydrogen and CO varied from 48% to 0%. Unstable flames due to preferential diffusion effects were observed for lean mixtures of fuel with high hydrogen content. The present results indicate that H2 has a strong influence on the combustion of producer gas. More »»

### Publication Type: Conference Paper

Year of Publication Title

2019

G. K. S. Raghuram, Aravind, B., Jithin, E. V., Kumar, S., and Dr. Ratna Kishore V., “Numerical Investigation on Combustion Characteristics of Premixed H 2/Air in Stepped Micro-Combustors”, in National Conference on IC Engines and Combustion, 2019.[Abstract]

Burning properties of premixed H<sub>2</sub>/air mixtures in single-stepped micro-combustor were numerically analysed. A detailed H<sub>2</sub>/air combustion mechanism of with nine species and 21 elementary reactions was used to model the combustion chemistry. Both laminar and turbulent models are considered for the analysis. The effect of inlet velocity (v) and step ratio on combustion characteristics and outer wall temperature (To_w) of combustor was studied. As step ratio is increased, the outer wall temperature of the combustor decreases due to the effect of lesser heat release rate and lesser transfer of heat flux for higher step ratio cases.

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### Publication Type: Conference Proceedings

Year of Publication Title

2014

Babu Namboothiri K. and Dr. Ratna Kishore V., “Effect of Solidity and airfoil on performance of Vertical Axis Water Turbine”, Proceedings International Conference on Energy and Sustainability in Engineering Systems (ICESES 2014). CIT, Coimbatore, Tamilnadu, pp. 49-54, 2014.

2014

B. M. M. S. R. S., Dr. Ratna Kishore V., Dr. Anbuudayasankar S. P., and Balaji K., “Power Generation by High Head Water in a Building using Micro Hydro Turbine”, International Conference for Energy and Environment. JNTU Hyderabad, 2014.[Abstract]

Demand for green energy production is arising all over the world. A lot of emphasis is laid in making the buildings green. Even a small amount of energy savings made contribute to saving the environment. In this study, an idea is proposed and studied to extract power from the high head water in the pipelines of a building. A building of height 15 m is considered for this study. Water flowing in the pipe has sufficient energy to run a micro hydro turbine. The feasibility of producing electrical energy from the energy of pipe water is found. The motivation is to find the feasibility of generating power using a low-cost turbine. The experimental setup consists of micro turbine of 135 mm diameter coupled to a 12-V DC generator; LEDs and resistors are employed to validate the results. The theoretical calculations were presented using the fundamental equations of fluid mechanics. The theoretical results are validated using experimental and numerical results using CFD simulation. In addition, exergy analysis has been carried out to quantify the irreversibilities during the process in the system. © 2015 Springer-Verlag Berlin Heidelberg

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## Research Projects

1. Title: Measurement of burning velocities of hydrocarbon hydrogen mixtures and application to Premixed laminar burner design (PI)
Funding Agency: DST
1. Title: Pool Thermal Hydraulics Investigations of FBR 1 and 2
(Co-PI)
Funding Agency: IGCAR (Indira Gandhi Centre for Atomic Research)
1. Title: Transfroming Global Health through Computational Cookstove Design (PI)
Funding Agency: Royal Academy of Engineering, UK

## List of Ph. D. Students

Current

1. Anoop – CB.EN.D*EEE17008
2. Unnikrishnan - CB.EN.D*MEE11004

Completed

1. V. Jithin - CB.EN.D*MEE15004
Faculty Research Interest: