Influence of Secondary Diaphragm on Flow Quality in Expansion Tubes

Experiments are described in which the influence of secondary diaphragm thickness and pre-deformation on Pitot and sidewall (static) pressures are investigated. The University of Queensland TQ expansion tube facility was operated in shock tube mode with argon as the driver and test gases. The results suggest that shock reflections between the diaphragm and the driver-test gas interface can cause disturbances to be propagated into the test gas flow, causing early termination of the run. This is best avoided by using diaphragms which are as thin as possible and pre-deformed prior to the run.