Robust non-reflecting boundary conditions for the simulation of rocket nozzle flow

A three-dimensional formulation of non-reflecting boundary conditions for the simulation of compressible flow is proposed and has been implemented in a second-order finite-volume Reynolds Averaged Navier–Stokes (RANS) solver and validated against the exact solution of an acoustic pulse propagation in a uniform flow. Satisfactory results are attained even for the higher amplitude of the acoustic pulse considered. In particular, the results show that the large pressure disturbances exiting the computational domain exhibit little spurious reflections. The motivation of this work is to demonstrate the applicability of the present method to compute rocket nozzle flow in rather small computational domains, characterized by a strong entrained flow (inflow) and outgoing jet (outflow) regions across the artificial boundary. Hence, unsteady RANS simulations of the internal flow and discharge zone of an overexpanded rocket nozzle at prescribed nozzle pressure ratios, have been performed. Comparison of the flow structure and major frequency content obtained with a reduced computational domain and the corresponding solution obtained in large domains with far artificial boundaries, confirms the robustness and accuracy of the present approach.