Max's Research

Flow Visualization of the Elastic
Taylor-Couette Instability in Boger Fluids

Flow between concentric, rotating cylinders (i.e., Taylor-Couette flow) is a classical, hydrodynamic stability problem. In Newtonian fluids, when the inner cylinder is rotated at low rates (or low Reynolds numbers), the flow is a purely azimuthal shearin g flow; fluid elements travel along circular streamlines between the two cylinders. At a critical rotation speed, however, centrifugal forces destabilize this flow and it is replaced by a toroidal vortex flow. In viscoelastic fluids, elasticity in the absence of centrifugal forces can lead to an instability. Below, we present experimental results showing the onset and evolution of the viscoelastic instability in constant-viscosity, highly elastic (i.e., Bo ger) fluids. The fluid was seeded with mica and illuminated with a sheet of laser light. Digital images of the flow between the cylinders were captured with a CCD camera; typically, each frame of a movie represents an average of many individual frames s o that the movies appear "time-lapsed". The first movie is an animation indicating the flow geometry and the evolution of the instability. All subsequent movies have been rotated by 90 degrees so that the inner cylinder appears at the bottom of the scr een and the outer (stationary) cylinder appears at the top.