An experimental investigation of the sonic criterion for transition from regular to Mach reflection of weak shock waves
Date
1985
Authors
Lock, Gary David
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Abstract
The signal speed, i.e. the sound speed plus the particle velocity, behind weak reflected shock waves has been measured for several shock strengths close to the point of transition from regular to Mach reflection. The signal speed was measured using a schlieren system to photograph acoustic signals created by a spark discharge or by a shallow crevice in the reflecting surface. Additionally, signal speed measurements were made using pressure gauges. The results from both methods yielded equal values within experimental error. The theoretical signal speeds behind the regularly reflected shocks were calculated using a non-stationary model and agreed with the measured values at large angles of incidence. As the signal speed approached the speed of the shock reflection point the measured values of the signal speed deviated significantly from the theorectical predictions. It was found that, within experimental uncertainty, transition from regular to Mach reflection of weak shock waves occured at the experimentally observed sonic point, i.e. when the signal speed was equal to the speed of the shock reflection point, and this sonic point did not coincide with the theoretical value.