Response of a Transitioning Hypersonic Boundary Layer to Repetitive Laser–Surface Interactions

Experiments were conducted in the University of Tennessee Space Institute’s Mach 7 Ludwieg tube, examining the impact of laser–surface interactions on the transitioning boundary layer on a 91-6 flared cone with Formula: see text million per meter. Laser–surface interactions were created using a pulse burst laser system operating with a 1064 nm output at repetition rates of 50, 100, 200, and 400 kHz. Global flowfield effects were visualized using high-speed schlieren imaging, and high-response surface pressure sensors were used to monitor changes in boundary-layer spectral content. Results show that for both weak and strong laser–surface interactions (as defined in this work), a significant reduction in boundary-layer fluctuations at higher frequencies occurs, which is also accompanied by a shift to larger turbulent structures and a thickening of the boundary layer. In strong interactions, it is also shown that significant separation can occur and that wraparound effects can even cause boundary-layer thickening and transition impacts on the nonincident side of the model.