Irregular reflection of weak acoustic shock pulses on rigid boundaries

Abstract

The reflection of weak shockwaves on rigid boundaries at grazing angles was studied in different geometrical configurations. It was shown that even in the case of weak shocks, irregular reflection of N-waves can lead to the formation of a three shocks pattern with a Mach stem, a triple point above the rigid surface and an angle reflection which differs from the incident one. Experiments were done using spark generated spherical shock waves with peak pressure lower than 10 kPa. Reflection patterns of shocks were obtained using a Schlieren visualization setup. Both regular and irregular regimes of reflection were observed. Numerical simulations of the nonlinear propagation were also performed. They were based on the high-order finite difference solution of the two dimensional Navier-Stokes equations. Optical measurements were compared with the results of simulations. Both experimental and numerical results showed the growth of the Mach stem with the distance of propagation. In the case of a randomly or periodically rough surface, the Mach stem is shorter, and nonlinear interactions between reflected waves occurs. [This work was supported by the Labex Centre Lyonnais d’Acoustique of Université de Lyon, operated by the French National Research Agency (ANR-10-LABX-0060/ANR-11-IDEX-0007).]