On the Accuracy of Turbulent Base Flow Predictions,
NIELSEN ENGINEERING AND RESEARCH INC MOUNTAIN VIEW CA
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Flow in the afterbody region of a supersonic vehicle with propulsive jets iss difficult to predict accurately partly because the complex pattern of shocks, expansion fans, and free shear layers is difficult to resolve, and partly because the turbulence is difficult to model. This report addresses problems of numerical resolution and turbulence modeling and shows that, while insufficient resolution causes some errors, larger errors can be attributed to the turbulence model. The standard k-epsilon model gives good results for one set of experimental data despite its inability to model many effects on the turbulence which may be present in the base region. A modification for Mach number effects is derived and verified against experimental data for plane shear layers. When the modified model is used to compute the base flow, the predicted base pressure rises significantly. This suggests that good results with the standard k-epsilon model are due to fortuitous error cancellation.
- Fluid Mechanics