Fluid Mechanics and Stability

Turbulent, dense fluid-particle flows are commonly encountered in engineering processes such as in air jet mills as well as terrestrial and extra-terrestrial phenomena, e.g., bedload sediment transport, movement of sand dunes, impingement of jets on planetary surfaces. High speed fluid flows on dense beds are complex in nature because of the coupling between the fluid and solid phases.

The Himalayan glaciers are a source of fresh water for millions. So the possibility of them retreating, given the accelerated pace of climate change, is a dire one. Moreover, the melting of the glaciers could translate into a rise in flash floods. Predicting the behaviour of glaciers, however, is a difficult task, due to a dearth of data (although recent campaigns have been launched to remedy this) and a lack of fundamental understanding of the mechanics of glacial flows.

The project envisages an experimental and CFD investigation of the stability of thin films of liquid flowing down inclined solid surfaces. Such flows frequently display a plethora of regimes as the flow rate is increased (meandering, braiding and many more) and knowledge of these leads to improved mass and heat transfer predictions in many industrial applications [1]. The stability of such flows sensitively depends on the wettability of the solid surface by the liquid. In this project, the student will build upon work by an existing Ph.D. student in the lab.

This project is a large scale CFD (LES - large eddy simulation) investigation of wind-generated ocean waves leading to wave breaking leading to sea spray formation [1]. The work will be jointly supervised with two other faculty members at IIT Madras (Prof. Anubhab Roy) and IIT Ropar (Prof. Devranjan Simanta). The student is expected to simulate wind generation of waves and turbulence in the uppermost layer of the ocean, wave breaking, bubble entrapment and fragmentation, bubble bursting and aerosol spray formation using LES based tools.

The phenomenon of ultrasonic atomisation was first reported by Wood and Loomis nearly a century ago in 1927 [1] and since then has been extensively used for various purposes [2] like pulmonary drug delivery [3], preparation of fine powders [4], combustion of liquid fuels [5], ultrasonic spray pyrolysis [6] to name only a few. In this method of atomisation, mechanical energy transmitted from a rapidly vibrating piezoelectric crystal (in the ultrasonic regime) to a liquid layer in contact with it, causes large capillary waves to develop at the surface of the liquid.