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

Dr. Sivadas V. comes to Amrita with national and international experience and reputation. He received his Ph. D. from IIT Bombay, specializing in Transverse Turbulent Jets utilizing optical diagnostic techniques. He was a Council of Scientific and Industrial Research (CSIR) Fellow while at IIT. 

In 1991, he worked as a German Academic Exchange Service (DAAD) Fellow at the German Aerospace Research Establishment (DLR)-Gottingen. This was followed by a Portuguese Science and Technology Fellowship in 2000 in the area of sprays and liquid film disintegration at the Insituto Superior Technico (IST) in Lisbon, Portugal under the European Commission DIME (Dynamics of Institution and Markets in Europe) program. The project focused on direct injection spray engine processes and mechanisms to improve performance. As part of this project, he participated in a short-course on the latest advances in Spray Technology at Carnegie Mellon University, USA under Professor Norman Chigier. 

Before joining Amrita, Dr. Vayalakkara worked at Nanyang Technological University in Singapore teaching courses in Mathematics and Fluid Mechanics and doing research in Surface Wave Dynamics under the Singapore-Stanford Partnership (SSP) with Stanford University, USA. 

He is a member of the American Association for the Advancement of Science and has been featured in Who's Who in the World and Who's Who in Finance and Industry.

Publications

Publication Type: Journal Article

Year of Publication Title

2020

Dr. Sivadas V., Balaji K., Vishwakarma, A., and Manikandan, S. Ram, “Experimental Characterization of a Liquid Jet Emanating From An Effervescent Atomizer”, Journal of Fluids Engineering, Transactions of the ASME, vol. 142, no. 6, pp. 064501 (1-7), 2020.[Abstract]


The study focuses on experimental characterization of the primary atomization associated with an effervescent atomizer. Unlike the existing designs available in the literature that inject air perpendicular to the liquid flow direction, the present atomizer design utilizes coflowing air configuration. In doing so, the aerodynamic shear at the liquid–gas interface create instability and enhance the subsequent jet breakup. Both integrated and intrinsic properties of the liquid jet were extracted by utilizing high-speed flow visualization techniques. The integrated property consists of breakup length, while the intrinsic property involves primary and intermediate breakup frequencies. The primary instability is characterized by low-frequency sinusoidal mode, whereas the intermediate instability consists of high-frequency dilatational mode. Dimensionless plots of these parameters with Weber number ratio leads to a better collapse of data, thereby generating appropriate universal functions. The combined diagram of frequencies converge with increasing relative velocity. This may be due to the dominance of energy consuming sinusoidal wave as the aerodynamic shear increases.

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2020

Dr. Sivadas V., Karthick, S., and Balaji K., “Symmetric and Asymmetric Disturbances in the Rayleigh Zone of an Air-Assisted Liquid Sheet: Theoretical and Experimental Analysis”, Journal of Fluids Engineering, Transactions of the ASME, vol. 142, no. 7, pp. 071302 (1-12), 2020.[Abstract]


The temporal analysis of symmetric (dilatational) and asymmetric (sinusoidal) perturbations at the interface of a water sheet in a co-flowing air stream focuses on low gas Weber number region (Weg < 0.4), namely Rayleigh breakup zone. The motive for this investigation is to acquire a better insight of breakup phenomena involved, rather than technical relevance, by utilizing Kelvin-Helmholtz instability. Accordingly, perturbations are introduced on the basic flow whose stability is to be examined by the method of normal (Fourier) modes. The temporal growth-rate of perturbations are traced to extract the wavenumber associated with maximum growth-rate. Thus, the critical wave-length, in conjunction with the phase velocity of the disturbance will facilitate to obtain the corresponding breakup frequency of the liquid sheet. The analytical findings on liquid sheet breakup frequency with increasing Weber number ratio exhibit the dominance of symmetric wave over asymmetric wave. It also shows independent evolution of breakup frequency with respect to Weber number ratio for the respective perturbation modes, which appears to be a pointed profile. That is, the frequency contour for dilatational mode dips, whereas it rises for the sinusoidal mode and at the Weber number ratio of 0.518 the crossover occur. The theoretical results were substantiated by high speed flow visualization studies that discerns the coexistence of low-frequency (primary) and high-frequency (intermediate) breakup events. Furthermore, the empirical average frequency data tracks reasonably well with the dilatational instability.

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2018

Balaji K., Dr. Sivadas V., Radhakrishna, V., A.B., K., and Saicharan, K., “Experimental Characterization of Intrinsic Properties Associated with Air-Assisted Liquid Jet and Liquid Sheet”, Journal of Fluids Engineering, Transactions of the American Society of Mechanical Engineers (ASME), vol. 140, no. 5, pp. 051301/1-9 , 2018.[Abstract]


The present study focuses on experimental characterization of interfacial instability pertinent to liquid jet and liquid sheet in the first wind-induced zone. To accomplish this objective, the interfacial wave growth rate, critical wave number, and breakup frequency associated with air-assisted atomizer systems were extracted by utilizing high-speed flow visualization techniques. For a range of liquid to gas velocities tested, nondimensionalization with appropriate variables generates the corresponding correlation functions. These functions enable to make an effective comparison between interfacial wave developments for liquid jet and sheet configurations. It exhibits liquid sheets superiority over liquid jets in the breakup processes leading to efficient atomization.

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2016

Dr. Sivadas V., Balaji K., Sampathkumar, Mc, Hassan, M. Md, Karthik, K. Me, and Saidileep, Kb, “Empirical Correlation of the Primary Stability Variable of Liquid Jet and Liquid Sheet under Acoustic Field”, Journal of Fluids Engineering, Transactions of the ASME, vol. 138, 2016.[Abstract]


The investigation focuses on optimizing the length of wind-pipe that transmits acoustic energy from the compression driver to the cavity of twin-fluid atomizers. To accomplish this objective, the primary variable of stability, that is, the breakup length of liquid jet and sheet under acoustic perturbations has been experimentally characterized for a range of wind-pipe length and liquid velocity. The analysis considers liquid phase Weber number in the range of 0.7-8, and the results are compared with primary breakup data without acoustic perturbations. The range of Weber number tested belongs to Rayleigh breakup zone, so that inertia force is negligible compared to surface tension force. It shows the existence of unique stability functions based on dimensionless products up to an optimum wind-pipe length, which extends greater for liquid sheet configuration. The present results may find relevance in atomizer design that utilizes acoustic source to enhance liquid column breakup processes. More »»

2013

Dr. Sivadas V., Aravind, R., Vignesh, E., Krishnaraj, I., and Balaji, K., “Area Void Fraction Associated with Twin-Fluid Atomizer”, Atomization and Sprays , Begell House, vol. 23, no. 8, pp. 663-676, 2013.[Abstract]


An empirical characterization of the void fraction in the spray region of liquid jets emanating from a twin-fluid atomizer has been carried out. The present study evolves under primary breakup criteria. That is, the respective breakup length extracted from flow visualization techniques are successfully utilized to find a better functional correlation for the area void fraction with longitudinal distance. The resultant function enables extracting the axial location at which complete atomization occurs for the range of conditions tested. To make the analysis more appealing in the practical domain, the concept of effective jet diameter and associated stretching factor at the nozzle exit plane were introduced. Hence, the validity of results will not be limited to the present test conditions.

 

 

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Publication Type: Patent

Year of Publication Title

2019

Dr. Sivadas V., Balaji Kalaiarasu, and Avinash Kumar, “An apparatus for disintegrating liquid into fine droplets (Patent Filed: 201941028906)”, 2019.

Faculty Research Interest: