SUPERPOSED FLOW BETWEEN 2 DISKS CONTRAROTATING AT DIFFERENTIAL SPEEDS

This paper describes a combined computational and experimental study of the flow between two contrarotating discs for -1 less than or equal to Gamma less than or equal to 0 (where Gamma is the ratio of the speed of the slower disc to that of the faster one) for the case where there is a superposed radial outflow of air. The computations were conducted using an elliptic solver and a low-Reynolds-number k-epsilon turbulence model, and velocity measurements were made using a laser-Doppler anemometry system. Two basic flow structures can occur: Batchelor-type flow, where there are separate boundary layers on each disc with a rotating core of fluid between, and Stewartson-type flow, where there is virtually no core rotation. The main effect of a superposed flow is to reduce the core rotation and to promote the transition from Batchelor-type flow to Stewartson-type flow. For most of the results, there is good agreement between the computed and measured velocities. Computed moment coefficients show that, for Gamma = -1, superposed flow has little effect on C-m: an accepted correlation of C-m for a free disc should provide a useful estimate for design purposes.