Experiments on the wall-pressure history in shock-reflexion processes

Abstract

The normal reflexion of a plane shock wave from a plane wall is investigated experimentally using a new pressure gauge which has a rise time of 0.1 μsec and no overshoot. Wall-pressure histories of 5 μsec duration can be obtained with the present version of this gauge. The experiments were conducted on the end wall of the GALCIT 17 in. diameter shock tube.Experimental results for three aspects of the reflexion process are presented and discussed: (1) effect of a cold wall, (2) effect of a vibrationally relaxing gas, and (3) profile for a reflecting shock front.It is concluded that the effect of a cold wall introduces a comparatively minor perturbation to the wall-pressure history, since the ‘thickness’ of the shock-front profile exhibited by the wall-pressure history is comparable to the ‘thickness’ of the incident shock front, as measured by a stationary observer, and the pressure jump across the profile is about 90% of the theoretical value for a thermally insulated wall. Also, the wall-pressure history immediately behind the reflected shock front can be approximated by boundary-layer theory. The effect of a vibrationally relaxing gas was studied in carbon dioxide, and it is shown that the relaxation process behind the incident shock wave produces a large effect on the recorded pressure history, which provides a method for measuring the vibrational relaxation time in carbon dioxide at high temperatures.