Control of incident shock

Experiments were carried out to control an incident shock-induced separation associated with 22° shock generator in a Mach 3.5 flow using an array of steady micro-jet actuators. Four micro-jet actuator configurations based on the variation in their pitch angle ( β ) , skew angle ( α ) and span-wise spacing were used. Each of these configurations were placed 14δ upstream of the interaction and operated with injection pressures (Poj) varying from 140 to 643？kPa. While no major variations in separation characteristics were observed for Poj？<？140？kPa, significant modifications were observed beyond P oj of 140？kPa and until 208.5？kPa. Amongst all the four control configurations, micro-jet vortex generator 2 ( α = 180 ° ; β = 45 ° ) showed the best control with a 2δ downstream shift in separation point location relative to no-control. The shift is also accompanied with a change in maximum zero-crossing frequency towards higher frequency (almost twice), a reduction in the intermittency length and an increase in the correlation value between the boundary layer just upstream of the interaction and the intermittent region. These results indicate that the effectiveness of micro-jet vortex generator 2 is probably due to the improved entrainment levels in the shear layer induced by the micro-vortices which are generated downstream of these devices. The increase of the skew angle ( α ) from 180° to 270° for the same pitch angle of β？=？45° (micro-jet vortex generator 3) seems to have no major impact on the separation characteristics. The reduction in the span-wise spacing (micro-jet vortex generator 4) resulted in deterioration of the flow field due to the jet-to-jet interaction with increasing injection pressures