This award supports Professor Andreas Acrivos of the City College of New York to collaborate with Professor Uwe Schaflinger of the Institute of Fluid Dynamics and Heat Transfer, Technical University of Vienna, in a study of the hydrodynamic stability of a resuspended layer. Several graduate students and postdoctoral associates of Dr. Acrivos will participate in the project. It has recently been established that under laminar conditions an initially settled bed of solid particles is resuspended due to action of shear. Further experiments have shown that the interface between the resuspended layer and the clear fluid becomes unstable due to interfacial waves. The aim of the proposed cooperative research is to combine numerical calculations with carefully directed experiments in order to verify the theoretical prediction of a transition from a spatially to an absolutely unstable flow and to gain insight into the mechanisms responsible for the creation and the breakup of the waves. The research will use an experimental setup designed and built by Dr. Schaflinger to study the basic resuspension flow in a two dimensional channel. He and his group in Vienna are very experienced with experimental techniques, analytical and numerical methods in fluid dynamics and specifically in two phase flows. Complementing this is the internationally recognized expertise of the group at CCNY in the fields of shear induced migration of particles, hydrodynamic stability and rheology. Their ongoing theoretical investigation of viscous resuspension will be greatly enhanced by this experimental collaboration. Resuspension plays an important role in most sediment transport phenomena, including industrial problems such as cross flow microfiltration. The conditions under which a settled layer of negatively buoyant particles will resuspend are not well understood and are usually associated with turbulence at high Reynolds numbers. Resuspension can also occur at low Reynolds numbers for which inertial effects are insignificant and the flow is laminar. This project will produce a systematic study of the instabilities at the interface of two superposed stratified fluids by adjusting the parameters of the flow in accordance with the ongoing analytical and numerical investigations at CCNY. It should result in fundamental insights into viscous resuspension and the stability of multiphase flows.
