TRANSITIONAL FLOW BETWEEN CONTRA-ROTATING DISKS

This paper describes a combined computational and experimental study o f the flow between contra-rotating disks for -1 less than or equal to Gamma less than or equal to 0 and Re phi 10(5), where Gamma is the rat io of the speed of the slower disk to that of the faster one and Re ph i is the rotational Reynolds number of the faster disk. For Gamma = 0, the rotor-stator case, laminar and turbulent computations and experim ental measurements show that laminar Batchelor-type flow occurs: there is radial outflow in a boundary layer on the rotating disk, inflow on the stationary disk and a rotating core of fluid between. For Gamma = -1, the laminar computations produce Batchelor-type flow: there is ra dial outflow on both disks and inflow in a free shear layer in the mid -plane, on either side of which is a rotating core of fluid. The turbu lent computations and the velocity measurements for Gamma = -1 show St ewartson-type flow: radial outflow occurs in laminar boundary layers o n the disks and inflow occurs in a non-rotating turbulent core between the boundary layers. For intermediate values of Gamma, transition fro m Batchelor-type flow to Stewartson-type flow is associated with a two -cell structure, the two-cells being separated by a streamline that st agnates on the slower disk; Batchelor-type flow occurs radially outwar d of the stagnation point and Stewartson-type flow radially inward. Th e turbulent computations are mainly in good agreement with the measure d velocities for Gamma= 0 and Gamma = -1, where either Batchelor-type flow or Stewartson-type flow occurs; there is less good agreement at i ntermediate values of Gamma, particularly for Gamma = -0.4 where the d ouble transition of Batchelor-type flow to Stewartson-type flow and la minar to turbulent flow occurs in the two-cell structure.