Numerical investigation of turbulent gas flow in an over-expanded nozzle flows: hysteresis phenomenon and asymmetrical configuration

Abstract

The flow in an Over-Expanded Nozzle is subjected to shock waves leading to the unsteady separation of the boundary layer. Free detachment may be followed by a restricted detachment. During the expansion regime in propellant nozzles, several physical phenomena are encountered: supersonic jet, jet separation, adverse pressure gradient, shockwave, turbulent boundary layer, highly compressible mixture layer, return flow, large-scale turbulence. These very complex phenomena can considerably affect the performance of the nozzle. This numerical study contributes to the analysis of the character of the detachment as well as the transition from one type of detachment to the other, and the numerical precision of the different models of turbulence that can predict the properties and physical phenomena of the flow in a flat nozzle. The study was conducted on a test case of the ATAC project {Aerodynamics of the Hoses and Backsbodies}. Girard [1], using a CFD-Fastran calculation code, based on the resolution of the Navier-Stokes equations by the finite volume method. The study highlights the phenomen on hysteresis and the asymmetrical configuration due to the detachment of the boundary layer.