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Prof. Gautam Biswas

Indian Institute of Technology Kanpur (India)

TitleThe Regimes between Partially Coalescing and Splashing Drops

Prof. Gautam Biswas
Prof. Gautam Biswas is presently a JC Bose National Fellow at the Department of Mechanical Engineering of Indian Institute of Technology Kanpur. He has served as the Director of the Indian Institute of Technology Guwahati, and of the CSIR-Central Mechanical Engineering Research Institute (CMERI) at Durgapur. He was the G.D. and V.M. Mehta Endowed Chair Professor, and Dean of academic affairs at IIT Kanpur.
Prof. Biswas was a Humboldt Fellow in Germany in 1987 and 1988; and JSPS invited fellow in Japan 1994. He is a Fellow of the American Society of Mechanical Engineers (ASME). He has served a full term as the Associate Editor of the Journal of Heat Transfer (Trans ASME). He was a Guest Professor at the University of Erlangen-Nuremberg in 2002. Currently he is Associate Editor of a well-known CFD-Journal— Computer and Fluids.
Prof Gautam Biswas is a Fellow of the all three major Science Academies of India, such as, the Indian National Science Academy (INSA), New Delhi, the Indian Academy of Sciences (IAS, Bangalore) and the National Academy of Sciences India (NASI). He is a Fellow of the Indian National Academy of Engineering (INAE) and Institution of Engineers India (IEI). He has been awarded the esteemed J.C. Bose National Fellowship by the Science and Engineering Research Board (DST), New Delhi. He is a fellow of the Asian Union of Thermal Science and Engineering (AUTSE). Prof. Biswas was bestowed with Distinguished Alumnus Award by IIEST, Shibpur in the year 2013. He has been awarded the Distinguished Alumnus Award by the Indian Institute of Technology Kharagpur in 2016. Prof. Biswas was conferred the Honorary Doctorate (Honoris Causa) by the National Institute of Technology Agartala, India, in 2017. He has also been conferred the Honorary Doctorate by the Aristotle University of Thessaloniki, Greece, in the year 2018.
In recognition of his stellar contributions in the fields of Fluid Mechanics and Thermal Sciences, his contributions as an academic administrator and his dedicated service to the institute, IIT Kanpur, on the occasion of its Foundation Day (Nov 2, 2021), conferred upon Professor Gautam Biswas the award of INSTITUTE FELLOW for the year 2020.
The Indian Institute of Technology Kanpur conferred the Distinguished Teacher Award for the year 2022 on Professor Biswas.
Worthington (1896) first explained different paradigms of drop impact on a liquid pool, using high-speed photography. When a drop of a liquid passes through air and impacts on the liquid-air interface of a liquid pool, depending on the size and velocity of the drop, it may coalesce partially or completely. Based on the shape of the crater and its expansion and contraction time, the final outcome can be partial coalescence, complete coalescence, jet formation with or without bubble entrapment, and splashing. In the case of droplet trains, long slender cavity formation due to multiple drop impacts on a deep liquid pool are observed.
When the drop of a liquid falls through a gaseous medium to eventually hit the gas-liquid interface, its initial impact on the interface can produce daughter drops of the liquid entailing occurrence of partial coalescence. In some cases, a partial coalescence cascade governed by self-similar capillary-inertial dynamics is observed, where the fall of the secondary droplets in turn continues to produce further daughter droplets. When a drop impinges on the surface of a deep liquid and quietly coalesces, complete coalescence occurs.
The transition between coalescence and splashing proceeds via a number of intermediate steps, such as thick and thin jet formation and gas-bubble entrapment. We perform simulations to determine the conditions under which bubble entrapment and jet formation occur.
Large bubble entrapment takes place if the prolate shaped drop impacts onto a liquid pool. This talk focuses on the identification of the large bubble entrapment regime. The researchers have classified different forms of the bubble entrapment scenario on a velocity versus drop-diameter map (V-D map). On the traditional classification map, the large bubble entrapment zone occupies a small region. The entrapment of a large bubble has been identified to be a vortex driven phenomenon. The vortex deforms the interface and produces an elongated roll jet, which then collapses on the central axis to entrap the large bubble. This talk attempts to explain the exact regime of large bubble entrapment on the V-D map.
The transition regimes between complete-coalescence and splashing of drops include jet formation with single or multiple secondary (tip) drops. One of the main features in this regime is the formation of a central liquid jet followed by breakup of the jet in the form of tip-drops. Earlier studies have shown that the diameter of the secondary (tip) drop lies between 0.58 and 0.94 times the diameter of the impacting drop. We perform investigations based on a coupled level-set and volume-of-fluid method to elucidate the earlier observations. The investigations reveal the creation of a variety of secondary (tip) drops depending on the impact conditions. The present study also reveals that secondary (tip) drops, larger than the initial drop, can be obtained at higher impact velocities. We identify the importance of capillary forces and cavity shapes on the formation of jets and other pertinent parameters that are responsible for drop ejection.