Transient, Hypervelocity Flow in an Axisymmetric Nozzle

Abstract : This study examines the performance of an axisymmetric nozzle which was designed to produce uniform, parallel flow with a nominal Mach number of 8. A free-piston-driven shock tube was used to supply the nozzle with high temperature, high pressure test gas. Performance was assessed by measuring Pitot pressures across the exit plane of the nozzle. The nozzle produced satisfactory test flows. However, there were flow disturbances that persisted for significant times after flow initiation. The detailed starting process of the nozzle was also investigated by performing numerical simulations at several nominal test conditions. The classical description of the starting process, based on a quasi- one-dimensional model, provided a reasonable approximation and was used to demonstrate that the starting process could consume a significant fraction of the otherwise usable test gas. This was especially important at high operating enthalpies where nozzle supply conditions were maintained for shorter times. Multidimensional simulations illustrated a mechanism by which the starting process in the actual nozzle could take longer than that predicted by the quasi- one-dimensional analysis.