Response of a Transitioning Axisymmetric Hypersonic Boundary Layer to Sequential Laser-Surface Interactions

Experiments were conducted in the UTSI Mach 7 Ludwieg tube examining the impact of laser-surface interactions on the transitioning boundary layer on a 91-6 flared cone with $Re_\infty=$ 8.0 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 kHz, 100 kHz, 200 kHz, and 400 kHz. Global flow-field 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 wrap-around effects can even cause boundary layer thickening and transition impacts on the non-incident side of the model.