Real gas effects on regions of viscous-inviscid interaction in hypervelocity flows

Abstract

In this paper, we examine a number of hypervelocity flows where real gas effects can influence the flow structure and aerothermal loads developed in regions of viscous/invis cid interaction. A brief review is also presented of the phenomena associated with shock wave/turbulent boundary interaction in hypersonic flows and the problems that arise in modeling these flows. Real-gas effects can exert a significant influence on the aerothermal loads developed in hypervelocity flows where the gas is processed through a series of shocks or in a region of expanding flow. Such flows arise principally as a result of shock/shock or shock/ boundary layer interaction or in strongly expanding flows such as those developed at the trailing edge of the Space Shuttle in the base region of a planetary probe. The effects of flowfield chemistry on laminar interacting flows over compression and expansion surfaces are discussed with particular reference to the control surface problems associated with the American Space Shuttle. A similar set of flow phenomena were examined in a study of real gas flows over a large blunt cone flare configuration. Here the emphasis was on the expanding flow downstream of the spherical nose tip and the flow 'separation generated at the cone/flare junction. Measurements made in these studies were compared with computations with a Navier-Stokes code incorporating real gas effects. The near wake flow behind a planetary probe configuration can be influenced by real gas effects generated in the expansion region immediately behind the body and the reattachment compression process at the neck of the wake. We review measurements made in the base flow region of a sting mounted planetary probe configuration conducted in air and nitrogen at velocities of 10,000 ft/sec and 14,000 ft/sec. Theoretical predictions of the aerothermal loads generated in regions of shock/shock interaction has suggested that real gas effects can significantly enhance the peak aerothermal loads; however, these conclusions are not totally supported by the results of recent experimental studies. We review the results of these studies for flows where a planar shock is incident on the stagnation region over a blunt cylinder, and on the shock/shock interaction region developed over an idealized indented nose tip. Finally, we present a brief review of the problems in predicting characteristics of regions of shock wave-turbulent boundary interaction in hypersonic flow. Here we review the basic characteristics of these flows and discuss important effects associated with boundary layer transition, low Reynolds number, and the compressibility effects, as well as the intrinsic unsteadiness of these flows.