Numerical Prediction of Flow Separation in an overexpanded nozzle

Abstract

A rocket engine nozzle is a propelling nozzle through which combustion gases are expanded and accelerated to supersonic velocities. For high thrust performance, the energy released by the propellants in the combustion chamber is converted into kinetic energy which leads to extremely high heat flux levels and temperature. These heat loads and temperatures may damage the nozzle wall and lead to loss in performance of the engine. Additionally, when the gases are expanded through the nozzle from subsonic to supersonic conditions, the flow under goes many forms of unique phenomena including flow separation and its associated shock system, unsteadiness, flow mixing etc. Some of these phenomena may lead to pressure loss, thereby reduce the overall thrust generated by the nozzle. The present work aims to provide a numerical analysis of flow separation in an overexpanded nozzle and the influence of wall temperature on a free shock-induced separation and thrust performance. The numerical method used is based on a finite volume scheme where the equations of Navier-Stokes, energy and turbulence were averaged in a Favre form using Ansys-Fluent®.