Control of shock unsteadiness in shock boundary-layer interaction on a compression corner using mechanical vortex generators

An experimental study was conducted to control the unsteadiness of separation shock in a Mach 2 24° compression ramp-induced interaction using mechanical vortex generators (VG). Control devices in the form of an array of single-row delta-ramps were placed upstream of the interaction region and tested for two streamwise locations with respect to the boundary layer thickness (δ) at the interaction location and height ‘h’ of the delta-ramps, i.e., at 27.5δ or h/δ = 0.65 and at 12.5δ or h/δ = 0.26, respectively. Surface oil study revealed traces of streamwise counter-rotating vortex pairs generated downstream of these devices. Measurements using pressure-sensitive paint also showed a spanwise sinusoidal pattern of wall pressure variation indicating generation of streamwise vortices from these control devices. These vortices, on interaction with the reverse flow in the separation bubble, replaced a well-defined separation line (for no control) by a highly corrugated separation line. In the region of separation, the mean pressure distribution gets modified while the peak rms value in the intermittent region of separation showed significant changes. Additionally, the spanwise spacing ‘s’ of the vertex of the delta ramps seemed to be an important parameter in controlling the peak rms value. A decrease in this spacing, i.e., VG1 with s =  0, significantly reduced the peak rms value (by 50 and 35 %) while an increase in the spacing, i.e., VG2 with s =  1 mm, consistently showed an increase (by 12 and 30 %) in the separation shock unsteadiness relative to no control, irrespective of their placement location (of h/δ = 0.65 and 0.26, respectively).