Flow instabilities and transition to turbulence in particulate Taylor-Couette flow

In this study, we present an experimental investigation into the influence of suspended particles on flow instabilities and transition to turbulence in Taylor-Couette (TC) flow with a rotating inner cylinder and stationary outer cylinder. The apparatus has a radius ratio of \eta=r_i/r_o=0.882, where r_i and r_o are the radii of the inner and outer cylinders, and an aspect ratio of \Gamma=L/\delta=37.9, where L is the height of the inner cylinder, and \delta=r_o-r_i is the annular gap size. The suspensions are formed of non-Brownian particles of equal density to the suspending Newtonian fluid, and the ratio of the annular gap to the mean particle diameter (d_p) is \alpha=\delta/d_p= 20.5. The Reynolds number is varied over a large range (30\le Re \le4000), covering laminar and turbulent flow transitions for several particle volume fractions (0\le \phi \le0.30). For \alpha=20.5, we show that particles play a fundamental role in the observed instabilities and decrease the threshold at which turbulence can be sustained.