Numerical Simulation of Internal Flow Transition in a Rocket Nozzle

Abstract

This work is a first step in the understanding of the interaction process between internal shock waves and the flow transition inside of a rocket nozzle during the start-up process or when it is operated under strongly over-expanded conditions. The interaction process produces a transition in the flow pattern, which in many cases generates side loads in the nozzle due to a change in the pressure distribution on the wall, being harmful for the rocket integrity. In order to understand the process a numerical simulation is carried out by solving the three dimensional Euler equations. With this tridimensional model the computational cost significantly increases, therefore parallel processing is required. Also, an unsteady h-adaptive refinement strategy is used jointly with a SUPG (Streamline Upwind Petrov-Galerkin) and
discontinuity capturing scheme, both to keep the mesh size bounded and to sharply resolve the shock wave pattern. The adapted mesh is non-conforming and a smooth size transition among neighbour elements
with different levels of refinement is enforced by means of refinement constraints. Computed average wall pressure distributions for various nozzle pressure ratios and at different time instants are compared. The simulations are carried out using the PETSc-FEM software.