Effect of inertial migration of particles on flow transitions of a suspension Taylor-Couette flow

The influence of inertial migration of neutrally buoyant particles on inertial flow transitions in Taylor-Couette (TC) flow of a suspensions is studied; this work considers primarily transitions associated with the circular Couette flow (CCF) and Taylor vortex flow (TVF) regimes. A concentric cylinder Taylor-Couette device with a stationary outer cylinder and rotating inner cylinder is considered. The device has an inner to outer radius ratio of eta = d(i)/d(o) = 0.877, where d(i) and d(o) are the inner and outer diameters of the flow annulus. The ratio of the axial length to the radial gap of the annulus Gamma = L/delta = 20.5, where delta = (d(o) - d(i))/2. The ratio of radial gap delta and the particle diameter d(p) is alpha = delta/d(p) = 30.4 and the particle volume fraction considered in this work is phi = 0.10. A flow structure (CCF or TVF) near the transition boundary with either uniform distribution across the annular region or fully migrated concentration profile is established. The Reynolds number (Re) is subjected to a rapid step change to study the effect of the concentration profile on the flow transition Re and resulting flow structure evolution; here the Reynolds number is Re = delta d(i)omega(i)rho/2 mu(s) , where omega(i) is the rotation rate of the inner cylinder and rho and mu(s) are the density and effective viscosity of the suspension. Our results show that, relative to uniform concentration, the particle distribution following inertial migration destabilizes the CCF state near the CCF-nonaxisymmetric flow transition boundary. In contrast to this destabilizing effect in CCF, migration of particles in the TVF regime has a stabilizing effect on the TVF-wavy Taylor vortex and TVF-nonaxisymmetric flow transition boundaries. The transition away from the TVF exhibits clear hysteresis associated with migration, as once initiated TVF could be sustained below and above the transition boundaries observed for suspension TC flow with uniform concentration.