Research

Complex Fluid Dynamics

My lab is interested in the flow and mechanics of complex fluids, such as granular materials, particle-liquid suspensions, and soft solids. They are encountered widely in industrial processes and natural phenomena, yet our understanding of their mechanics is far more rudimentary than that of fluids. Equally, they pose interesting scientific challenges, as theoretical models for these systems are still in a stage of development. We use a combination of theory, experiments, and particle dynamics simulations in our studies. Our focus is to build reliable continuum mechanical descriptions, and to obtain a fundamental mechanistic understanding by relating observable macroscopic properties to processes at the particle scale.

Modelling Dense Granular Flow

We have developed theoretical models for slow dense flows of granular materials which repair deficiencies of existing classical plasticity-based models. In our earlier work, we repaired the deficiency of kinematic indeterminacy by treating the granular material as a Cosserat continuum for which we have provided experimental evidence. Recently, we have proposed an alternative non-local model that captures shear-driven dilatancy, which no previous model has done.

Secondary Flows

We developed a sensitive technique to conduct experimental rheometry of granular materials, and used it to determine the stress variation with depth in a cylindrical Couette device. We show that all components of the stress rise exponentially with depth. With high-speed imaging and particle dynamics simulations, we demonstrated the emergence of a novel secondary flow in the form of a single system-spanning toroidal vortex. We showed that the secondary flow is driven by dilatancy, which has no analogue in fluids.