Toward Supersonic Retropropulsion CFD Validation

Abstract

This paper begins the process of verifying and validating computational fluid dynamics (CFD) codes for supersonic retropropulsive flows. Four CFD codes (DPLR, FUN3D, OVERFLOW, and US3D) are used to perform various numerical and physical modeling studies toward the goal of comparing predictions with a wind tunnel experiment specifically designed to support CFD validation. Numerical studies run the gamut in rigor from code-to-code comparisons to observed order-of-accuracy tests. Results indicate that this complex flowfield, involving time-dependent shocks and vortex shedding, design order of accuracy is not clearly evident. Also explored is the extent of physical modeling necessary to predict the salient flowfield features found in high-speed Schlieren images and surface pressure measurements taken during the validation experiment. Physical modeling studies include geometric items such as wind tunnel wall and sting mount interference, as well as turbulence modeling that ranges from a RANS (Reynolds-Averaged Navier-Stokes) 2-equation model to DES (Detached Eddy Simulation) models. These studies indicate that tunnel wall interference is minimal for the cases investigated; model mounting hardware effects are confined to the aft end of the model; and sparse grid resolution and turbulence modeling can damp or entirely dissipate the unsteadiness of this self-excited flow.

Supersonic Retropropulsion Experimental Results from NASA Ames 9×7 Foot Supersonic Wind Tunnel

“…A myriad of papers have recently been published that provide detailed post-test CFD comparisons to the experimental results, for instance see Refs. [13][14][15][16][17][18]. Also, additional experimental results have recently been published in Refs.…”

Computational Fluid Dynamics Validation and Post-test Analysis of Supersonic Retropropulsion in the Ames 9x7 Unitary Tunnel

“…8,9 This process used the LaRC UPWT test 10 and the uncertainty analysis 24 that came from it. The focus of the present paper, for the Ames Unitary test, is to implement these established best practices and evaluate SRP at higher thrust coefficients (C T > 3) and lower freestream Mach numbers.…”

“…9 The case that was focused on was Run 165, M = 4.6 and C T = 2. Each code captured different variations of the unsteady oscillation of the triple point, which created pressure waves that propagated both to the model and to the bow shock.…”

Supersonic Retropropulsion Experimental Results from the NASA Langley Unitary Plan Wind Tunnel

“…Subsequent sections will provide a quick review of the test and preliminary observations relevant to the SRP experimental data. While this paper is focused strictly on experimental results, separate papers [11][12][13] will provide post-test computations with comparisons to data.…”