Control of Stationary Cross-flow Modes Using Patterned Roughness at Mach 3.5

Abstract

Spanwise-periodic roughness designed to excite selected wave lengths of stationary cross-flow modes was investigated in a 3-D boundary layer at Mach 3.5. The test model was a sharp-tipped 14° right-circular cone. The model and integrated sensor traversing system were placed in the Mach 3.5 Supersonic Low Disturbance Tunnel (SLDT) equipped with a “quiet design” nozzle at NASA Langley RC. The model was oriented at a 4.2° angle of attack to produce a mean cross-flow velocity component in the boundary layer over the cone. Three removable cone tips have been investigated. One has a smooth surface that is used to document the baseline (“natural”) conditions. The other two have minute “dimples” that are equally spaced around the circumference, at a streamwise location that is just upstream of the linear stability neutral growth branch for cross flow modes. The azimuthal mode numbers of the dimpled tips were selected to either enhance the most amplified wave numbers or to suppress the growth of the most amplified wave numbers. The results indicate that the stationary cross-flow modes were highly receptive to the patterned roughness.