No abstract

No abstract

At the 2001 AIAA Aerospace Sciences Meeting there was a blind comparison between computational simulations and experimental data for hypersonic double-cone and hollow cylinder-flare flows. This code validation exercise showed that in general there was good agreement between the continuum CFD simulations and experiments. Also, in general, there was good agreement between direct simulation Monte Carlo (DSMC) calculations and the experiments in regions of attached flow. However, in almost all of the computations, the heat transfer rate on the forebody of the cone was over-predicted by about 20%. The purpose of this paper is to report on our analysis of this difference. We perform CFD simulations of the hypersonic nozzle flow to assess the importance of vibrational nonequilibrium on the test conditions. We then recompute the flows using a new set of vibrational nonequilibrium conditions and consider the effects of a slip boundary condition at the model surface. Additionally, we analyze new heat transfer rate data on sharp and blunt 25° cones over a wider range of test conditions. This analysis appears to explain the discrepancy between the previous calculations and the experiments. IntroductionAt the 2001 AIAA Aerospace Sciences Meeting, there was a session dedicated to a CFD code validation study. A number of computational researchers used their methods to predict the flow over several hypersonic configurations, and then the experimental data were revealed and compared to the computations. Two geometries were tested: a hollow-cylinder / flare that produces a weak viscous interaction, and a double-cone that produces a much more complicated flow field with a stronger viscous-inviscid interaction. The test conditions were chosen so that the free-stream conditions would be well characterized and the flows would be entirely laminar. Also to reduce the complexity of the computational analysis, nitrogen was used as the test gas.This blind code validation study resulted in several key conclusions: First, the comparisons between the continuum computations and experiments were generally very good. For example, consider Fig. 1 which is taken from the paper of Harvey, Holden, and Wadhams.1 The predicted surface pressure and heat transfer rate are plotted against the experimental data at two test conditions. Note that the pressure matches well on the cone forebody, through the separation zone, in the region of high pressure due to the shock-shock interaction, and on the second cone. Similarly for the heat transfer rate, with very good agreement in the separation zone, the shock interaction region, and on the second cone. The main differences are that the heat transfer rate on the cone forebody is overpredicted by about 20% and the separation zone is slightly too large, which results in the peak of pressure and heat transfer being too far downstream. The continuum computations by the other researchers showed essentially the same features, and additional calcula-

No abstract