Journal of Fluid Mechanics Webinar Series: Jesse Capecelatro, USA and Saksham Sharma, UK

Speaker: Jesse Capecelatro, University of Michigan, USA

Date/Time: Friday 30th April 2021 4:00pm BST/11am EST

Title: Turbulence modeling of strongly-coupled gas-particle flows

Abstract: Many natural and industrial processes involve the flow of solid particles or liquid droplets whose dynamical evolution are intimately coupled with a carrier gas. A peculiar behavior of such flows is their ability to give rise to large-scale structures (hundreds to thousands of times the size of individual particles), from dense clusters to nearly-particle-free voids. Seminal works by G.K. Batchelor has provided theoretical estimates describing the motion of collections of particles suspended in viscous flows and the notion of hindered settling under gravity. In this talk I will describe how at moderate Reynolds numbers and concentrations, momentum exchange between the phases results in enhanced settling and the generation of turbulence in the carrier phase. High-resolution simulations will be presented to reveal how multiphase interactions at the particle scale augment or restrict large-scale flow processes, and provide unique insight into the budget of turbulent kinetic energy. Finally, a new data-driven framework will be presented for model closure of the averaged two-phase flow equations.

Speaker: Saksham Sharma, University of Cambridge, UK

Date/Time: Friday 30th April 2021 4:30pm BST/11:30am EST

Title: On a toroidal method to solve the sessile drop oscillation problem

Abstract: The natural oscillation of a drop is a classical fluid mechanics problem. Analytical expressions for the simple case of free, spherical drops were obtained by Rayleigh, Lamb, Chandrasekhar and others using spherical coordinate system. In recent times, the focus on this problem has shifted towards a sessile drop supported on a flat substrate, as evident through some recent works. The majority of these are computational in nature. In this talk, I will present an alternative new mathematical framework, the toroidal coordinate system, to solve this long-standing problem analytically for small drops (Bond number << 1) with pinned contact lines. I start with the governing hydrodynamic equations and boundary conditions, write them in terms of the toroidal coordinate system and then obtain solutions by reducing them to an eigenmode problem. Resonant frequencies are identified for zonal, sectoral and tesseral vibration modes and compared with results presented in the literature and by other models. The impact of viscous dissipation in the bulk liquid, at the contact line, and contact line mobility is discussed qualitatively. I conclude with a discussion of the importance of conformal mapping for solving axisymmetric physical problems with complicated geometries.