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

Dr. Laxman Vaitla currently serves as Assistant Professor at the Department of Aerospace Engineering, School of Engineering, Amrita Vishwa Vidyapeetham, Coimbatore. Dr. Laxman Vaitla worked as a Postdoctoral Fellow at Seoul National University in the School of Mechanical and Aerospace Engineering and Konkuk University in the Department of Aerospace and Information Engineering from 2010- '11 and from 2008- '10, respectively. He has received his Ph. D. in 2008 and M. Tech. in 2002 from Indian Institute of Technology (IIT) Kanpur. His primary area of interest is structural dynamics and aeroelasticity (mostly on rotary-wing aeroelasticity).

Education

  • 2008: Ph.D., Aerospace Engineering,
    Indian Institute of Technology, Kanpur, UP
    Emphasis: Formulation of a Computational Aeroelastic Model for the Prediction of Trim and Response of a Helicopter Rotor System in Forward Flight
  • 2002: M. Tech., Aerospace Engineering,
    Indian Institute of Technology, Kanpur, UP
    Emphasis: Structural Dynamic Modeling and Analysis of a Hingeless Rotor Blade
  • 1999: B.Tech., Civil Engineering,
    Jawaharlal Nehru Technical University, Hyderabad, AP

Areas of Research Interest

  • Helicopter Rotor Dynamics
  • Wind Turbine Blade Dynamics
  • Structural Dynamics and Aero-elasticity

Areas of Teaching Interest

UG Level :

  • Mechanics of Solids
  • Vibration Analysis
  • Finite Element Methods
  • Engineering Mechanics
  • Engineering Graphics

PG Level :

  • Vibration of Continuous Systems
  • Continuum Mechanics
  • Structural Dynamics and aero-elasticity
  • Helicopter Dynamics
  • Nonlinear Finite Element Method

Publications

Publication Type: Journal Article

Year of Publication Title

2019

B. Mantravadi, Unnikrishnan D., Sriram, K., Mohammad, A., Dr. Laxman Vaitla, and Velamati, R. Kishore, “Effect of solidity and airfoil on the performance of vertical axis wind turbine under fluctuating wind conditions”, International Journal of Green Energy, 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 = 1 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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2018

R. Sankarasubramanian, Sridhar, A., Prashanth, M. S., Mohammad, A., Velamati, R. K., 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. © 2018 Elsevier Masson SAS

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2018

G. Srikumar, Srikrishnan, V. A., Purushothaman, R. K., Thiagarajan, V., Velamati, R. K., 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. © 2018 American Society of Civil Engineers.

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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 < 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 ( > 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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2016

M. M. S. R. S. Bhargav, V. Kishore, R., and Dr. Laxman Vaitla, “Influence of fluctuating wind conditions on vertical axis wind turbine using a three dimensional CFD model”, Journal of Wind Engineering and Industrial Aerodynamics, vol. 158, pp. 98-108, 2016.[Abstract]


In practical situations, it is important to analyze the performance of VAWT considering the fluctuations of free stream wind. In the present paper, 3D unsteady numerical analysis is employed to investigate the effect of fluctuating wind conditions on the performance of a 1.1 kW commercially viable VAWT. VAWT is 3 straight bladed, Darrieus type having NACA 0015 airfoil profile. Turbulence is modeled using Transition SST K-ω model. Free stream velocity U∞ is varied in sinusoidal manner with respect to flow time for Umean=10 m/s. In this study, the effect of variation of fluctuation amplitude Uamp, fluctuation frequency fc and tip speed ratio λon the performance of VAWT is investigated. The vortex structures are studied for Uamp =10% and 50%. From the results, it is observed that the uniform and fluctuating wind CP curves do not trace each other. Cycle averaged CP increases with Uamp. A maximum CP of 0.33 is obtained corresponding to Uamp =50%. Cycle averaged CP increases to a maximum value and then decreases with λmean. Maximum CP of 0.31 is obtained corresponding to λmean=2. Cycle averaged CP increases to a maximum value and then marginally decreases with fc. Maximum CP of 0.31 is obtained corresponding to fc =1 Hz. Hence the overall performance under fluctuating wind conditions improved when VAWT is operated at higher Uamp, λmean≥2 and fc close to 1 Hz. © 2016 Elsevier Ltd

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2014

J. H. Lim, Shin, S. J., Dr. Laxman Vaitla, Kim, J., and Jang, J. S., “Development of an improved framework for the conceptual design of a rotorcraft”, Aircraft Engineering and Aerospace Technology: An International Journal, vol. 86, pp. 375–384, 2014.[Abstract]


Purpose: The purpose of the present paper is to obtain the capability of designing modern rotorcrafts with enhanced accuracy and reliability.

Design/methodology/approach: Among the existing rotorcraft design programs, an appropriate program was selected as a baseline for improvement. It was based on a database comprising conventional fleets of rotorcrafts. The baseline program was not robust because it contained a simple iteration loop, which only monitored the gross weight of the aircraft. Therefore, it is not accurate enough to fulfill the quality and sophistication of a conceptual design framework useful for present and future generations of rotorcrafts. In this paper, the estimation formulas for the sizing and weight of the rotorcraft subsystem were updated by referring to modern aircraft data. In addition, trend curves for various turboshaft engines available these days were established. Instead of using the power estimation algorithm based on the momentum theory with empirical corrections, blade element rotor aerodynamics and trim analysis were developed and incorporated into the present framework. Moreover, the simple iteration loop for the aircraft gross weight was reinforced by adding a mathematical optimization algorithm, such as a genetic algorithm.

Findings: The improved optimization framework for rotorcraft conceptual design which has the capability of designing modern rotorcrafts with enhanced accuracy and reliability was constructed by using MATLAB optimization toolbox.

Practical implications: The optimization framework can be used by the rotorcraft industries at an early stage of the rotorcraft design.

Originality/value: It was verified that the improved optimization framework for the rotorcraft conceptual design has the capability of designing modern rotorcrafts with enhanced accuracy and reliability.

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2013

Dr. Laxman Vaitla, Venkatesan, C., and Byun, Y. H., “Influence of blade geometric parameters on aeroelastic response of a helicopter rotor system”, Journal of Aerospace Engineering, vol. 26, no. 3, pp. 555-570, 2013.[Abstract]


Rotary wing aeroelasticity is a highly complex phenomenon involving coupling between flexible blade dynamics and unsteady aerodynamics including stall and unsteady wake effects. In this paper, a low-cost computational aeroelastic model including the structural coupling from geometric parameters and nonlinearities associated with structural modeling and dynamic stall, applicable to steady, level forward flight, has been developed. The differential equations of motion are solved in time domain in a sequential manner to obtain the response of all the blades in the rotor system, the dynamic inflow variables, and the sectional loads at every time step. A fourth-order Runge-Kutta integration scheme has been adopted for solving the differential equations. Iterations are carried out until convergence is achieved in blade response and helicopter trim. The effect of blade geometric parameters such as pretwist, hinge offset, and torque offset on aeroelastic response of a helicopter rotor system is investigated numerically. It is shown that the structural coupling from blade geometric parameters significantly influences the rotor blade response and loads. © 2013 American Society of Civil Engineers.

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2011

Dr. Laxman Vaitla, Lim, J. H., Shin, S. J., Ko, K. H., and Jung, S. N., “Power and Trim Estimation for Helicopter Sizing and Performance Analysis”, International Journal of Aeronautical and Space Sciences, vol. 12, no. 2, pp. 134 -140, 2011.[Abstract]


The preliminary design stage of helicopters consists of various operations and in each operation design several detailed analysis tasks are needed. The analysis tasks include performance and the required power estimation. In helicopter design, those are usually carried out by adopting the momentum theory. In this paper, an explicit form of computational analysis based on the blade element theory and uniform/non-uniform inflow model is developed. The other motivation of the present development is to obtain trim and required power estimation for various helicopter configurations. Sectional and hub loads, power, trim, and flapping equations are derived by using a symbolic tool. Iterative computations are carried out till convergence is achieved in the blade response, inflow, and trim. The predictions regarding the trim and power estimation turn out to be correlated well with the experimental results. The effect of inflow is further investigated. It is found that the present prediction for the lateral cyclic pitch angle is improved with the non-uniform inflow model as compared to that by the uniform inflow model. The presently improved trim and power estimation will be useful for future helicopter sizing and performance analysis.

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2010

Dr. Laxman Vaitla, A, B., J., Y. K., and H., B. Y., “Improvement of the Parameterised Identification Model using Quasi-steady and Non-uniform Inflow Aerodynamic Models”, Journal of Aerospace Engineering, vol. 24, no. 3, pp. 378 – 388, 2010.[Abstract]


Compared with those of a fixed-wing aircraft, the dynamics of a rotorcraft are significantly more complex. One of the major challenges in the design of an autonomous helicopter is the development of a flight dynamic model, which can be useful for simulation studies and for the design of control law and navigational aspects. There is always a trade-off from the accuracy of the mathematical model to the more simplified model required for a control design as far as the helicopter rotor/fuselage dynamics is concerned. Small-scale helicopters posses a higher bandwidth of dynamics; hence, models developed from the first principle alone do not fulfill the needs, and more-sophisticated mathematical models are thus required. The main objective of the present work is to improve the parameterized identification model by replacing it with a most-general flight dynamic model for a minihelicopter. This model includes the rotor blade flap dynamics, stabilizer bar dynamics, and vehicle dynamics, which will be applicable for a general maneuvering flight. A systematic study is undertaken to analyze the influence of inflow models and flap response on the helicopter trim. Stability of the minihelicopter is also analyzed; except for phugoid, all other modes are stable in hover and high forward flight conditions.

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2009

Dr. Laxman Vaitla and C, V., “Formulation of a Computational Aeroelastic Model to Predict Trim and Response of a Helicopter Rotor System”, Aerospace Sciences and Technologies, vol. 61, no. 3, pp. 415 -433, 2009.[Abstract]


Rotary wing aeroelasticity is a highly complex phenomenon involving coupling between flexible blade dynamics, unsteady aerodynamics including stall and unsteady wake effects.

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2009

Dr. Laxman Vaitla and Venkatesan, C., “Influence of Dynamic Stall and Dynamic Wake Effects on Helicopter Trim and Rotor Loads”, Journal of the American Helicopter Society, vol. 54, no. 3, pp. 1-18, 2009.[Abstract]


Flight test data of helicopters indicate that vibratory levels in the fuselage exhibit a wide spectrum of frequencies including the dominant blade passage frequency and its integer multiples. The present work attempts to understand the reason for the existence of several frequencies in the response of the fuselage and possible cause for this observed phenomenon by formulating a computational aeroelastic model. In this theoretical study, a systematic approach has been undertaken to identify the effects of inflow modeling and sectional aerodynamic load evaluation, on helicopter trim, rotor blade response, and hub loads. Five different combinations of aerodynamic models of increasing complexity, representing rotor inflow and sectional aerodynamic loads, have been proposed. The differential equations of motion are solved in time domain in a sequential manner to obtain the response of all the blades in the rotor system, the inflow variables, and the sectional loads at every time step. The results of the present study show that the aerodynamic model incorporating dynamic wake and dynamic stall effects introduces a wide spectrum of harmonics in the hub loads including blade passage frequency and its integer multiples. The influence of aerodynamic modeling on the variation of trim parameters with forward speed has also been brought out. It is observed that the aerodynamic model incorporating dynamic wake and dynamic stall effects predicts the trim parameters whose variation with forward speed resemble qualitatively similar to those obtained in flight test. A comparison of the variation of blade sectional lift for various aerodynamic models indicates that in the advancing side of the rotor, a dynamic stall model introduces a shift in the azimuth angle at which the minimum lift occurs. The effect of structural flap—lag coupling due to blade pretwist on trim and rotor loads has been studied, and these results are compared with those pertaining to a straight blade configuration.

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2007

Dr. Laxman Vaitla and Venkatesan, C., “Chaotic Response of an Airfoil due to Aeroelastic Coupling and Dynamic Stall”, Aiaa Journal - AIAA J, vol. 45, no. 1, pp. 271-280, 2007.[Abstract]


of helicopters indicate that vibratory levels in the fuselage exhibit a wide sprectrum of frequencies, including a few below the rotor revolutions per minute.

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Publication Type: Conference Proceedings

Year of Publication Title

2016

Dr. Laxman Vaitla, “Stall, Flutter and Thrust Generation of an Oscillating Airfoil”, Pravartana 2016: Symposium on Applied Mechanics, February 12. IIT Kanpur, India, 2016.

2014

N. K. Paramveer, SaiTharun, B., Akhil, A. V., and Dr. Laxman Vaitla, “Analysis of delamination propagation of stringer reinforced composite panel using VCCT”, in International Conference on Theoretical, Applied, Computational and Experimental Mechanics. IIT Kharagpur, India, 2014.

2014

Barathwaj N. C., Prashanth R., Ashwani P., Akhil A. V., and Dr. Laxman Vaitla, “Static aeroelastic analysis of composite wings”, International Conference on Theoretical, Applied, Computational and Experimental Mechanics, December 29 – 31. IIT Kharagpur, India, 2014.

2014

M. Anand, Dr. Laxman Vaitla, Devarajan, K., Balaji, R., Shrivathsan, K. S., and Adithiyakkumaran, D. A., “Structural dynamic model for a horizontal axis wind turbine system”, International Conference on Theoretical, Applied, Computational and Experimental Mechanics. IIT Kharagpur, India, 2014.

2011

Dr. Laxman Vaitla, Chung, C. H., Yoon, N. K., and SangJoon, S., “Aeroelastic Analysis of a Medium-Altitude Long-Endurance Aircraft with High-Aspect Ratio Wings”, International Forum on Aeroelasticity and Structural Dynamics. Paris, 2011.

2011

J. H. Lim, Shin, S. J., Dr. Laxman Vaitla, and Kim, J., “Improvement of a Rotorcraft Preliminary Design Optimization Framework”, 52nd AIAA/ASME/ASCE/AHS/ASC Structures, Structural dynamics and materials conference. 2011.

2010

C. Hoon Chung, Dr. Laxman Vaitla, Lee, J., and Joon, S. Sang, “고세장비 주익을 지닌 항공기의 공력탄성학 해석 (Aeroelastic study of an Aircraft Wing)”, The 40th Agency for Defense Development Foundation Anniversary Day General Academic Conference. Daejeon Convention Center, Daejeon, Korea., 2010.

2010

Dr. Laxman Vaitla, Chung, C. Hoon, Lee, J. Whan, Yoon, N. Kyung, and Shin, S. Joon, “Aeroelastic Analysis of an Aircraft with High-Aspect Ratio Wings”, Korean Society for Aeronautical and Space Sciences Conference. Jeju, South Korea, pp. 315–318, 2010.

2009

Dr. Laxman Vaitla, Budiyono, A., Yoon, K. J., and Byun, Y. H., “Improvement of the Parameterised Identification Model using Quasi-steady and Non-uniform Inflow Aerodynamic Models”, International Symposium on Intelligent Unmanned System. Jeju, South Korea, 2009.

2009

Dr. Laxman Vaitla and Venkatesan, C., “Influence of Dynamic Stall and Dynamic Wake Effects on Helicopter Trim and Rotor Loads”, AHS Specialist's Conference on Aeromechanics. Fisherman's Wharf, San Francisco, CA (USA)., 2009.[Abstract]


Flight test data of helicopters indicate that vibratory levels in the fuselage exhibit a wide spectrum of frequencies including the dominant blade passage frequency and its integer multiples. The present work attempts to understand the reason for the existence of several frequencies in the response of the fuselage and possible cause for this observed phenomenon by formulating a computational aeroelastic model. In this theoretical study, a systematic approach has been undertaken to identify the effects of inflow modeling and sectional aerodynamic load evaluation, on helicopter trim, rotor blade response, and hub loads. Five different combinations of aerodynamic models of increasing complexity, representing rotor inflow and sectional aerodynamic loads, have been proposed. The differential equations of motion are solved in time domain in a sequential manner to obtain the response of all the blades in the rotor system, the inflow variables, and the sectional loads at every time step. The results of the present study show that the aerodynamic model incorporating dynamic wake and dynamic stall effects introduces a wide spectrum of harmonics in the hub loads including blade passage frequency and its integer multiples. The influence of aerodynamic modeling on the variation of trim parameters with forward speed has also been brought out. It is observed that the aerodynamic model incorporating dynamic wake and dynamic stall effects predicts the trim parameters whose variation with forward speed resemble qualitatively similar to those obtained in flight test. A comparison of the variation of blade sectional lift for various aerodynamic models indicates that in the advancing side of the rotor, a dynamic stall model introduces a shift in the azimuth angle at which the minimum lift occurs. The effect of structural flap—lag coupling due to blade pretwist on trim and rotor loads has been studied, and these results are compared with those pertaining to a straight blade configuration.

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2009

Dr. Laxman Vaitla, H, B. Y., and C., V., “Effect of Blade Geometric Parameters on Aeroelastic Response of a Helicopter Rotor System in Hover and Forward Flight”, 3rd International Basic Research Conference on Rotorcraft Technology. China, 2009.

2009

R. M, Dr. Laxman Vaitla, and C, V., “Development of a Computational Aeroelastic Model for a Helicopter in Level Flight and Maneuvering Conditions”, IISc Centenary International Conference and Exhibition on Aerospace Engineering. IISc, Bangalore, 2009.

2009

Dr. Laxman Vaitla, C, V., and H, B. Y., “Effect of Couplings and Nonlinearities on Aeroelastic Response of a Helicopter Rotor System”, 2nd International Forum on Rotorcraft Multidisciplinary Technology. Korea, 2009.

2009

V. C. and Dr. Laxman Vaitla, “Computational Aeroelastic Formulation for Helicopter Rotor Loads”, Symposium on Applied Aerodynamics and Design of Aerospace Vehicle. Banglore, 2009.

2008

Dr. Laxman Vaitla and Venkatesan, C., “Aeroelastic modeling and analysis of a helicopter rotor blade including dynamic stall and wake effects”, International Conference on Aerospace Science and Technology (INCAST):NAL50. Bangalore, India., 2008.

2008

Dr. Laxman Vaitla and C, V., “Effect of Pretwist on Aeroelastic Response of a Rotor System with Dynamic Stall and Dynamic Wake”, 34th European Rotorcraft Forum. Liverpool, UK, 2008.

2007

Dr. Laxman Vaitla and C, V., “Aeroelastic Analysis of a Helicopter Rotor Blade Including Dynamic Stall and Dynamic Wake Effects”, International Conference on Theoretical, Applied, Computational and Experimental Mechanics. IIT Kharagpur, 2007.

2007

Dr. Laxman Vaitla and C, V., “Influence of Dynamic Stall on Aeroelastic Response of Airfoil Applicable for Rotary-Wing Vehicles”, Conference on Current Trends in Engineering Analysis and Design, DREAMS’07. Banglore, 2007.[Abstract]


Flight test data of helicopters indicate that vibratory levels in the fuselage exhibit a wide spectrum of frequencies including the dominant blade passage frequency and its integer multiples. The present work attempts to understand the reason for the existence of several frequencies in the response of the fuselage and possible cause for this observed phenomenon by formulating a computational aeroelastic model. In this study, dynamic stall and dynamic wake effects are incorporated in a coupled aeroelastic analysis to investigate blade sectional loads, hub loads and trim condition of the helicopter. The differential equations of motion are solved in time domain in a sequential manner to obtain the response of all the blades in the rotor system, the inflow variables, and the sectional loads at every time step. The influence of aerodynamic modeling on the trim condition and aeroelastic response of the rotor blade in forward flight has been brought out. It is found that the aerodynamic model incorporating dynamic wake and dynamic stall effects predict the trim parameters whose variation with forward speed resemble qualitatively similar to those obtained in flight test. A comparison of variation of blade sectional lift for various aerodynamic models indicates that in the advancing side of the rotor, dynamic stall effects introduce a shift in the azimuth angle at which the minimum lift occurs. It is also shown that the structural coupling due to blade pretwist significantly influences the rotor blade response and loads compared to an untwisted rotor blade. Copyright 2008 by the American Helicopter Society International, Inc. All rights reserved.

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2006

Dr. Laxman Vaitla and Venkatesan, C., “Rotor blade dynamic stall model and its influence on airfoil response”, 47th AIAA/ASME/ASCE/AHS/ASC Structures, Structural dynamics and materials conference, vol. 1866. Newport, Rhode Island (USA)., p. 2006, 2006.[Abstract]


Flight test data of helicopters indicate that vibratory levels in the fuselage exhibit a wide spectrum of frequencies including a few below the rotor RPM. It is well known that helicopter blades operate in a complex aerodynamic environment, involving time varying heave, pitch and pulsating oncoming flow. During operation, some sections of the rotor blade undergo dynamic stall once in a revolution. This paper attempts to understand the reason for the existence of several frequencies in the response of the fuselage and the possible cause for this observed phenomenon by analysing the effects of dynamic stall and aeroelastic couplings on the response of 2-D airfoil. The ONERA dynamic stall model developed by Petot is modified by incorporating a higher order rational approximation of Theodorsen's lift deficiency function. This improved model is shown to provide a better correlation with experimental stall data. The response characteristics of a 2-D airfoil undergoing pitching and plunging motion in a pulsating oncoming flow, simulating the response of a cross-section of a helicopter rotor blade in forward flight are analysed. This study shows significant difference in the response characteristics of the airfoil for unsteady (dynamic stall model) and quasi-steady aerodynamic models. It is observed that the non-linear aerodynamics (dynamic stall effects) in association with aeroelastic couplings above a certain level lead to a bounded chaotic motion of the airfoil.

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2005

Dr. Laxman Vaitla and C, V., “Dynamic Stall Models for Aeroelastic Analysis of Helicopter Rotor Blades”, International Conference on Computational and Engineering and Sciences. IIT Madras, 2005.

2005

Dr. Laxman Vaitla and Venkatesan, C., “Dynamic Stall Modeling and Its Effect on Airfoil Response”, Proceedings of the 11th International Workshop on Rotorcraft Dynamics and Aeroelasticity. 2005.[Abstract]


The field of rotary-wing aeroelasticity has been a very active area of research during the last four decades [1]. There are still several unresolved issues relating to blade loads and fuselage response in forward flight [2] and [3]. Analysis of rotary-wing aeroelasticity requires a proper structural, inertial and aerodynamic modeling. The rotor blade aerodynamic modeling is highly complex due to time varying pitch, heave, pulsating oncoming flow, dynamic stall and wake effect. Modeling of instantaneous sectional lift, drag and moment as a function of pitching, plunging motion of the blade, variation in oncoming velocity and inflow velocity is of paramount importance in evaluating rotor aerodynamic loads. Dynamic stall is a strong nonlinear unsteady aerodynamic effect associated with flow separation and reattachment. It is difficult to predict stall and all its effects using theoretical unsteady aerodynamic tools. So researchers are depending on the empirical or semi-empirical models. Several mathematical models that attempt to predict the effects of dynamic stall are available in the literature [4] - [8]. ONERAdynamic stall model is a relatively simple and efficient model to incorporate in aeroelastic analysis. The ONERA dynamic stall model developed by Petot is modified by incorporating a higher order rational approximation [9] of Theodorsen’s lift deficiency function [10]. This improved model is shown to provide a better correlation with experimental stall data [11] (Fig. 1). The response characteristics of a 2-D airfoil undergoing pitching and plunging motion in a pulsating oncoming flow, simulating the response of a cross-section of a helicopter rotor blade in forward flight are analysed (Fig. 2). This study shows significant difference in the response characteristics of the airfoil for unsteady (dynamic stall model) and quasi-steady aerodynamic models (Fig. 3). It has been observed that introduction of heave-pitch coupling by shifting the mass centre from the elastic centre results in the appearance of several sub and super harmonics in heave as well as in pitch response of the airfoil under dynamic stall conditions. The results pertaining to this analysis and also additional results of correlation will be presented in the final version of the paper.

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Publication Type: Book

Year of Publication Title

2005

Dr. Laxman Vaitla and Mohite, P., Mechanics of Solids. Hyderabad: Radiant Publishing House, 2005.

Awards & Honours

  1. Excellence in Teaching Award (2016-17) from Amrita School of Engineering.
  2. Postdoctoral fellowship under Brain Korea 21 program from 2010 to March 2011.
  3. Postdoctoral fellowship under Brain Korea 21 program from 2008 to March 2010.