First Trace for Irregular Shock Wave Process in Weak Mach Reflection

Referring to von Neumann's words, transition from a two- to a three-shock reflection configuration in the weak domain presents some very considerable theoretical difficulties. It nonetheless remains an observed fact that such a transition does indeed occur in the real world. This paper describes the novel experimental technique and the results which for the first time did yield a "footprint" that something quite out-of-the-ordinary is taking place within the base of the reflected wave where the latter butts the point of shock confluence. The results of the work presented here remained puzzling initially, for they seemed to contradict some preconceived outcome. It was only years later that the specific detail which was first considered to be misleading could be interpreted. It disclosed that the flow through the reflected shock is being forced to deviate from the classic Rankine-Hugoniot shock transformation process. This departure then enables the unyielding boundary conditions to be fulfilled and three-shock reflection to get established. This occurs with some lag past detachment of RR, this interval being required for the properties to adjust to the imposed conditions. The hypothesis of the departure from classic shock theory has been verified in the wind tunnel and was confirmed