Active Transonic Shock Control

Abstract

‡‡ * ‡ A transonic shock over a two-dimensional convex surface is indirectly manipulated in wind tunnel experiments by fluidic control of the shock-induced separated shear layer. Fluidic actuation is effected by a spanwise array of individually-controlled pulsed jets with a 1 ms scale. The flow upstream and downstream of the shock is characterized in detail using planar PIV and schlieren visualization that are accompanied by simultaneous surface pressure measurements, all of which are acquired phase-locked to the actuation waveform. Pulsed actuation leads to a momentary attachment of the separated shear layer which, in turn, effects a significant synchronized streamwise translation of the shock followed by a longer relaxation as the surface vorticity layer re-separates. Following the rapid displacement and distortion during the transitory onset of the actuation, the normal shock intensifies and transitions to a lambda shock when the actuation jets approach their full momentum. The present data show a strong correlation between the surface dynamic pressure and the shock position that is extracted from the PIV measurements. Furthermore, when the actuation is applied with a given jet velocity offset, the shock's nominal position is offset relative to the baseline flow (i.e., in the absence of actuation), and it continues to respond to time-dependent actuation relative to that offset position. These findings indicate that indirect control of shock induced separation can be exploited for shock stabilization and time-dependent positioning.