Shock wave interaction in hypervelocity flow

Citation

Sanderson, Simon Ralph (1995) Shock wave interaction in hypervelocity flow. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/3GPK-5G29. https://resolver.caltech.edu/CaltechETD:etd-11092004-094744

Abstract

The interaction of a weak oblique shock with the strong bow shock ahead of a blunt body in supersonic flow produces extreme heat transfer rates and surface pressures. Although the problem has been studied extensively in low enthalpy flows, the influences of high enthalpy real gas effects are poorly understood. Existing perfect gas models predict greatly increased heating with increasing Mach number and decreasing ratio of specific heats. Experiments are conducted in a free piston shock tunnel to determine the effects of thermochemistry on the problem at high enthalpy. The flow topology is simplified by studying the nominally two-dimensional flow about a cylinder with a coplanar impinging shock wave. High resolution holographic interferometry is used to investigate changes in the flow structure as the location of the impinging shock wave is varied. Fast response heat transfer gauges provide time resolved measurements of the model surface temperature. The data that are obtained do not support the existing predictions of greatly increased heat transfer at high enthalpy. A model is developed to study the thermochemical processes occurring in the interaction region. The phenomenon arises because the stagnation streamline is forced to pass through a system of oblique shock waves that produce less entropy than the undisturbed bow shock. Peak heating is shown to result from a balancing of the strengths of the oblique shock waves. This condition is demonstrated to simultaneously minimize the influence of thermochemistry on the flow. Real gas effects are shown to become important at lower Mach numbers (< 7.5) and for shock angles weaker or stronger than that which produces maximum heating. The model accurately reproduces the experimental observations. A nonequilibrium approximation is introduced that applies when the oblique waves are weak with respect to the undisturbed bow shock. Within the scope of the approximation, non-monotonic behavior with the reaction rate is predicted. The reaction rate is not varied as an independent parameter in the current experiments.

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