Effect of the Slot Orientation Angle on Stabilization of a Supersonic Boundary Layer

Abstract

An experimental study is performed on the influence of surface slots (grooves) with a depth of 0.18 mm (the depth-based Reynolds number is \({{\operatorname{Re} }_{h}} \approx 1000\)) with orientation angles \(\varphi = 0^\circ \), 30°, 45°, and 90° on the stability of a supersonic boundary layer on a flat plate. Experiments with natural disturbances at the free-stream Mach number \({\text{M}} = 2\) are performed. It is found that the maximum rates of the spatial growth of disturbances decrease as the slot orientation angle decreases from \(\varphi = 90^\circ \) to zero. At \(\varphi = 0^\circ \) and 30°, they become smaller than the corresponding values for a smooth plate. The results obtained show that the instability of the first mode of the supersonic boundary layer, which determines the laminar-turbulent transition at \({\text{M}} = 2\), can be stabilized by small-depth slots with moderate angles of their orientation (\(0^\circ \leqslant \varphi < 40^\circ \)).