Numerical Performance Prediction of a Miniature at Mach 4

Abstract

Using a 3-D axis-symmetric model, the cold-flow performance of a miniature ramjet in Mach 4 flow was predicted with the computational fluids dynamic (CFD) code from ANSYS-CFX. The nozzle-throat area was varied to increase the backpressure and this pushed the normal shock that was sitting within the inlet, out to the lip of the inlet cowl. Using the eddy dissipation combustion model in ANSYS-CFX, a combustion analysis was performed on the miniature ramjet. The analysis involved the single-step, stoichiometric combustion of hydrogen and oxygen within the combustion chamber of the ramjet. The drag force induced on the miniature ramjet when subjected to Mach 4 flow in a supersonic wind tunnel was measured using cryogenic strain gauges arranged in a Wheatstone bridge. A CFD cold-flow drag prediction was compared against this measured drag force to establish the formers accuracy in drag prediction. For all CFD predictions, the two-equation Shear-Stress-Transport (SST) turbulence model was used. The SST turbulence model blends the k-epsilon and k-omega turbulence model and effects the transportation of the turbulent shear stress for improved accuracy in turbulence modeling.