A study of shock wave diffraction from regular to irregular reflection and the effects of gas viscosity

A comprehensive experimental investigation was made of the pseudo-stationary reflection of strong, weak, and very weak shock waves in a monatomic gas. The experiments were designed to reduce the effects of viscosity and were further complemented by numerical computations. The experiments made use of symmetrical plane wedge models having either an internal corner or an external corner. The experimental results for the pseudo-stationary mutual reflection of strong shock waves produced by diffraction of strong incident shocks into internal corner models supported the mechanical equilibrium criterion for transition from regular reflection, RR, to irregular reflection, IR. The inviscid numerical computations also unequivocally supported the mechanical equilibrium criterion for strong shocks. The results for the external corner models displayed the well known persistence of RR which was attributed to the combined effects of viscosity and optical resolution. Within the IR region it was found that for strong shocks the results did not agree with the inviscid von Neumann three shock theory once the Mach number behind the reflected shock was less than unity. However, when the experimental models were reduced in width to leave boundary layer control slots the discrepancy was almost entirely eliminated. The limit of validity for the von Neumann three shock theory as the wedge angle was reduced was found to be the normal reflected shock point. For small wedge angles the experimental results for strong, weak, and very weak shock waves all showed similar behaviour which was consistent with the phenomena of von Neumann reflection, VNR. For smaller wedge angles this may undergo transtion to anomalous reflection, ANR, where the incidence angle remains constant for further reduction in wedge angle. A theory was developed to give the angle of the triple point trajectory path within VNR and also predict the transition point from VNR to ANR. This theory showed excellent agreement with both the experimental and numerical computation results. It is further shown that all IR transitions are governed by the solution of a single polynomial of degree four. Furthermore all irregular reflections may be considered as combinations of only three fundamental reflection types, these being, ANR, VNR, and classic (or single) Mach reflection, SMR. A theoretical consideration of plane wedge internal corner (symmetrical and unsymmetrical) reflection is given, and the types of reflections possible are discussed