Turbulent Taylor-Couette flow between independently rotating cylinders

We present experimental studies of the turbulent flow of water between independently rotating cylinders. The Taylor-Couette system is capable of both strong turbulence $(Re>10^6)$ and rapid rotation $(\mbox{Ek}<10^{-7})$. The torque required to drive the inner cylinder is precisely measured as a function of the two angular velocities \textit{$\Omega $}$_{i}$ and \textit{$\Omega $}$_{o}$. Of particular interest are three distinct regions of the (\textit{$\Omega $}$_{i}$, \textit{$\Omega $}$_{o})$ parameter space defined by the inner and outer boundaries having equal: ($i)$ angular velocities (solid-body rotation), (\textit{ii}) azimuthal velocities and (\textit{iii}) angular momenta (Rayleigh criterion) with the outer boundary stationary line (\textit{$\Omega $}$_{o }$= 0) serving as the final bound. We supplement the global torque measurements with local wall shear stress measurements as a means of detecting Coriolis-restored, linear inertial modes. We model the system as being composed of two interacting, turbulent boundary layers. There are several open questions that we hope to be able to answer: (1) Are there conditions under which angular momentum will flow uphill? (2) What quantity (angular velocity, azimuthal velocity, or angular momentum) does the system most effectively ``mix,'' and does that depend upon system parameters.