No abstract

Detailed experimental data are presented on the transition between regular and Mach reflexion. Data have been obtained for steady, pseudo-steady and un-steady flows, and include a study of the continuous and discontinuous transitions predicted by previous researchers. It is found that the criterion often used to calculate the transition condition is wrong in every case that we have investigated. In its place we propose an alternative criterion which has the property that the system remains always in mechanical equilibrium during transition.

"' p present results from our eX]Jerinwnts with the irregular l'efledion of shock wavps in argon. \Ve eompare the data with the results we obtained llullH'riealiy; the assnmptiollfl for the computational eoclt' were that. we had ullsteady. two-dimenRional, compressible, inviseid, flow of a perfect gas. \VIll'll precautions were taken to reduce the effects of the gas viscosity on the experimental data, we obtained very good agreement bdweell the numerieal and the experiment.al results for the ramp Maeh number and the trajectory path triple-point angle, but there were discrppaneies with the wave-angle data. The diserellaneies were ascribed to the scnsit ivity of tIl!' data to both viscosity and to a singularity. \Ve silow that t.here arc actually two weak irregular wave reflect.ions. namely a elassie Mach reflection (MR) and a 11e\Y type, t.hat we call a von Neumann reflection (NR). The structure of the NR is discussed in some det.aiL and so are the transition criteria for the various wa\Te systems.

We present the results of numerical computations of the refraction of a plane shock wave a t a CO,/CH, gas interface. The numerical method was an operator split version of a second-order Godunov method, with adaptive grid refinement. We solved the unsteady, two-dimensional, compressible, Euler equations numerically, assuming perfect gas equations of state, and comRared our results with the experiments of Abd-El-Fattah & Henderson. Good agrekment was usually obtained, especially when the contamination of the CH, ,by the GO, was taken into account. Remaining discrepancies were ascribed to the uncertainties in measuring certain wave angles, due to sharp curvature, poor definition, or short length of the waves at large angles of incidence. All the main features of the regular and irregular refractions were resolved numerically for shock strengths that were weak, intermediate, or strong. These include free precursor shock waves in the intermediate and strong cases, evanescent (smeared out) compressions in the.weak case, and the appearance of an extra expansion wave in the bound precursor refraction (BPR). The structure of a BPR was elucidated for the 4rst time.