Azimuthal velocity profiles in Rayleigh-stable Taylor-Couette flow and   implied axial angular momentum transport
  We present azimuthal velocity profiles measured in a Taylor-Couette apparatus, which has been used as a model of stellar and planetary accretion disks. The apparatus has a cylinder radius ratio of $\eta = 0.716$, an aspect-ratio of $\Gamma = 11.74$, and the plates closing the cylinders in the axial direction are attached to the outer cylinder. We investigate angular momentum transport and Ekman pumping in the Rayleigh-stable regime. The regime is linearly stable and is characterized by radially increasing specific angular momentum. We present several Rayleigh-stable profiles for shear Reynolds numbers $Re_S \sim O(10^5) \,$, both for $\Omega_i > \Omega_o > 0$ (quasi-Keplerian regime) and $\Omega_o > \Omega_i > 0$ (sub-rotating regime) where $\Omega_{i,o}$ is the inner/outer cylinder rotation rate. None of the velocity profiles matches the non-vortical laminar Taylor-Couette profile. The deviation from that profile increased as solid-body rotation is approached at fixed $Re_S$. Flow super-rotation, an angular velocity greater than that of both cylinders, is observed in the sub-rotating regime. The velocity profiles give lower bounds for the torques required to rotate the inner cylinder that were larger than the torques for the case of laminar Taylor-Couette flow. The quasi-Keplerian profiles are composed of a well mixed inner region, having approximately constant angular momentum, connected to an outer region in solid-body rotation with the outer cylinder and attached axial boundaries. These regions suggest that the angular momentum is transported axially to the axial boundaries. Therefore, Taylor-Couette flow with closing plates attached to the outer cylinder is an imperfect model for accretion disk flows, especially with regard to their stability. 
Freja Nordsiek, Sander G. Huisman, Roeland C. A. van der Veen, Chao   Sun, Detlef Lohse, Daniel P. Lathrop
physics.flu-dyn