Experimental study of inertioelastic Couette-Taylor instability modes in dilute and semidilute polymer solutions

Instabilities appearing in the circular Couette flow with a dilute or semidilute solution of high molecular weight polyethyleneoxide in water have been investigated when the outer cylinder is kept at rest. The shear-thinning behavior of solutions was determined through low shear viscosity measurements. We have found that, depending on concentration, different flow structures can appear at the onset of instability. For dilute concentrations, the critical mode is the stationary and axisymmetric Taylor vortex flow, which bifurcates to time periodic wavy vortex flow for a higher shear rate. The oscillation amplitude of wavy vortex flow decreased with the increasing shear rate. For sufficiently semidilute solutions, the critical mode occurs in the form of standing waves, the frequency of which decreases with the shear rate. The critical Taylor number increases for solutions without a shear-thinning effect and decreases for solutions exhibiting shear thinning. (C) 2002 American Institute of Physics.