Navier-Stokes and Experimental Modeling of Blunt-Base Rocket Nozzle Flow
The influence of grid placement and grid density on the ability to compute an underexpanded jet in a supersonic afterbody flowfield is studied using a conservation-based body-fitted computational technique. The thin-shear-layer formulation of the compressible, Reynolds-averaged, Navier-Stokes equations together with mass and energy conservation equations are modeled using an artificial time-dependent, explicit numerical algorithm with the turbulence approximated by a two-layer algebraic model with wall functions for the solid boundaries and whose properties are tailored to the three physically distinct mixing zones. Solutions are obtained for supersonic flow over an axisymmetric conical afterbody with a blunt base, containing a centered propulsive jet where the freestream Mach number is 2.0 and the jet exit Mach number is 2.5. Exhaust exit-plane static pressures are considered in the range of one to nine times the freestream static pressure. The conical nozzle-exit half-angles are zero and twenty degrees. Comparisons are made between computed and experimental results for base pressure, separation length, afterbody pressure distribution, and flowfield structure. The numerical solutions are found to be sensitive to the computational grid structure and the mixing (turbulence) model. Error norms are applied to aid the detection of inappropriate grid choices. The best results are obtained with adaptive grids that track both free shear layers and a mixing model which is germain to the local flow features.
KeywordsMach Number Computational Region Local Truncation Error Nozzle Flow Nozzle Pressure Ratio
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