Over the past few years, we have been working to develop new procedures based on force-coupling models than can give an accurate approximation for dispersed two-phase flows such as solid particles or bubbles in liquids. The models have been tested for a variety of viscous flow systems and we have extended them to provide a numerical simulation procedure for higher Reynolds number flows. These procedures also provide a systematic framework for developing engineering models and the interpretation of experiments. They are much faster and simpler to implement than full direct numerical simulations for a given problem and we can cover much larger systems than would be otherwise possible. We are applying these methods to study the dynamics of particle settling in suspensions at finite Reynolds numbers and for non-uniform suspensions in Stokes flow.
In a DARPA-sponsored project aimed at reducing drag on ship hulls, we are studying the dynamics of microbubbles injected into turbulent shear flows and how these may alter the near-wall flow. The technique of microbubble injection is known to work in laboratory experiments but to date there is little theory as to how drag reduction is achieved or how it might be scaled. Our simulations are providing new insights as to the range of bubble sizes that are relevant and the first evidence of drag reduction in numerical simulations.
It is now feasible to manipulate bio-particles and bio-molecules in ?lab on a microchip? systems for cell sorting or detection. These flows involve complex 3D geometries and we are now able to simulate accurately the particle motion in these flows and include particle-particle interactions and the effects of external forces used to manipulate the particles.