Inertio-elastic stability modifications with drag reducing polymeric solutions

The cascade of transitions separating laminar and turbulent flow in the Taylor Couette geometry was examined with drag reducing polymer solutions in the regime where the magnitude of the elastic forces approaches that of the inertial forces, i.e. where the elasticity number (El) nears unity. The elasticity number, defined as the ratio of a polymeric time scale to the viscous time scale, greatly impacts the stability boundaries of isolated secondary flow features in both the co- and counter-rotating Taylor Couette flow regimes. It was previously shown that for dilute poly(ethylene oxide) solutions with El≪1, the elasticity effect was non-monotonic, mode-dependent, and more significant for higher order states. In this study, Re_inner vs Re_outer stability planes generated at El∼1 in concentric, independently rotating cylinders of radius ratio 0.912 and aspect ratio of 60.7 are compared to previous maps generated in the inertia-dominated regime (El∼0). As a result, the importance of elasticity with solutions of similar diluteness is illuminated for various flow transitions, including transitions to axisymmetric, wavy, spiraling and/or turbulent modes. Changes in stability during adiabatic increases of the inner cylinder Reynolds number were determined using flow visualization and spectral analysis. All flow states are characterized by symmetry/symmetry breaking features as well as azimuthal and axial wave numbers using a combination of flow visualization in 2D planes of radial, axial, projected azimuthal and time dimensions. Polymeric solution characterization includes dynamic and steady shear and extensional flows, light scattering, and sessile drop experiments, and addresses such issues as chain scission, aggregation, and temperature dependence.