Effect of periodic blowing on attached and separated supersonic turbulent boundary layers

Periodic blowing at frequencies up to 5 kHz was used to control the unsteadiness of two-dimensional shockwave/ turbulent boundary-layer interactions. Two separate experiments were performed. In the first case, periodic blowing was introduced through a spanwise slot in the wall to produce an unsteady shock-wave/boundarylayer interaction boundary layer on the tunnel wall. In the second case, periodic blowing was introduced into the shock-induced separation bubble formed by a 24-deg compression corner interaction. The incoming flow conditions for both experiments were M_∞ = 2.84, Re_∞/l = 6.5 × 10⁷/m, and δ_o = 26 mm. Measurements of the fluctuating mass flux and wall pressure were made, and the unsteady flowfield was visualized through stroboscopic schlieren videography. The measurements were conditionally sampled based on the phase of the blowing cycle. The results suggest that (at least in this case) the naturally unsteady shock motion in the compression ramp interaction does not contribute significantly to the turbulence amplification, as had been previously thought. Instead, there is strong evidence to suggest that large-scale motions associated with the maxima in the angular momentum profiles in the downstream boundary layer are responsible for the large mixing observed.