Research Projects

Rationale: Particulate flows are ubiquitous in geophysical situations (clouds, dust storms, plankton in the ocean) and in industry. Direct numerical simulations of particulate flows, with proper accounting for the dynamics of each particle and all the physics, are going to be impossible for the decades to come, and so theoretical approaches combined with small simulations are going to be crucial. Though a lot of work has been done on small spherical non-interacting particles, our recent studies indicate that departures from sphericity and interparticle interactions are going to be important. Scientific objectives: In geophysical contexts such as clouds, duststorms and plankton in the ocean, we shall address the three C’s: particle clustering (or clumping), inter-particle cooperation, and caustics formation or estimates of collision. It is believed that raindrop growth, and hence rain itself, crucially depends on turbulence-mediated clustering, including the formation of caustics. Extremely little is known about the three C’s for non-spherical or non-ellipsoidal particles, and our recent study indicates that these processes could differ starkly. Understanding these is one important goal of this work. Particles in one-way coupling, i.e., with no back-reaction on the flow or on each other, are well studied. Our studies so far indicate that clumping due to interparticle interactions can be important, and we wish to study the three C processes under four-way-coupling. Our recent studies also point to the importance of a history force on particle clustering and caustics formation, and we plan to study these. We hope the findings will be of use to make practical estimates: of microplastic transport from Indian shores, of carbon sequestration by phytoplankton in the ocean, and dust levels in the atmosphere. Hypotheses: Sedimenting non-spherical particles will display qualitatively different and vastly enhanced collision rates. Interparticle interactions will greatly enhance cluster formation. History effects will be pronounced in ocean flows rather than in atmospheric flows. Simulations: Direct numerical simulations will be conducted of the incompressible Navier-Stokes equations with small interacting particles included as a continuum and as individual spheres, spheroids or di-bilaterals. Unsteady Stokes effects including the Basset-Boussinesq history will be studied. Estimate of significance The transport of non-spheroidal particles by turbulence is an open question. So too is inter-particle interactions in a dusty turbulent flow. The study will thus fill theoretical gaps in knowledge and be put to practical use.