Detailed investigation of the three-dimensional separation about a 6:1 prolate spheroid

The flow in the crossflow separation region of a 6:1 prolate spheroid at 10- and 20-deg angle of attack, Re-L = 4.20 x 10(6), was investigated using a novel, miniature, three dimensional, fiber-optic laser Doppler velocimeter (LDV). The probe was used to measure three simultaneous, orthogonal velocity components from within the model, and these measurements were simultaneous with wall-pressure measurements made just below the LDV probe volume. The LDV measurements extend from approximately y(+) = 7 out to beyond the boundary-layer edge. The design and operation of this LDV probe is summarized. Plots of velocity, skin friction, wall-flow angle, mean and fluctuating pressures, turbulent kinetic energy, helicity density, and secondary streamlines are used to show the location of separation and reattachment lines. These measurements are also used to show that a trough of fluid, which is quite distinct from the rest of the flow, exists just downstream of the separation sheet. This trough has fluid of very low mean and turbulent kinetic energy. Plots of the turbulence anisotropy show there to be little correlation between the flow-gradient and the turbulent-shear-stress angles over large regions of the flow. This implies that turbulence models employing the eddy viscosity concept cannot be adapted to three-dimensional separated flows such as this.