A PIV study on the effect of pulsed-jet injection upstream of a Mach 2 shock wave/turbulent boundary layer interaction

A wide-field PIV system was used to study the effects of upstream pulsed mass injection on a turbulent boundary layer/shock wave interaction generated by a 20° compression ramp in a Mach 2 flow. The mass injection was provided by three discrete pulsed underexpanded jets, which were located 60 mm upstream of the compression ramp and had a pulse-duration of 5 ms. The wide-field PIV was achieved by using four megapixel cameras to enable a field of view that spanned the upstream unperturbed boundary layer, injection jets, intermittent and separation regions, and compression ramp face. Phase-locked PIV measurements were taken with no injection and with a 4 ms delay with respect to the injection trigger signal. The phase-average PIV measurements show that the pulsed jets have a substantial impact on the upstream boundary layer and the structure of the interaction. For example, the PIV shows the bow shock upstream of the injectors and the expansion region downstream of them. Pulsed injection was found to move the interaction downstream about one quarter of a boundary layer thickness. This result implies the injectors act like vortex generators that introduce high momentum fluid into the upstream boundary layer and thus make it more resistant to separation.