Transition to Weak-Shock Solution Around Centerbody Using Laser Energy Deposition

In this study, the effects of thermal bubbles produced by repetitive laser pulses on a shock wave system over a cone with an apex angle of 40 & DEG; surrounded by a 19 mmx19 mm square duct in a Mach 1.97 flow were experimentally investigated. The shock wave system was controlled by changing the location of the conical centerbody. Depending on the blockage condition at the center, the shock wave over the cone exhibited either a weak or strong solution; moreover, in the intermediate condition, a dual-solution domain was observed. In a critical condition, the strong shock solution of the dual-solution domain could transition into a weak shock solution even after the entry of a single thermal bubble with an energy of 5.1 mJ. In other conditions, the transition was realized only by repetitively supplying thermal bubbles with an appropriate repetition frequency. At a center, e.g., the strong-to-weak transition was achieved with a repetition frequency of 30 kHz. However, at a frequency of 50 kHz, unfavorable interactions among the thermal bubbles resulted in unsuccessful transition.