Influence of Jet Pressure on Multi-nozzle Supersonic Retropropulsion Flowfields

Abstract

Multi-nozzle supersonic retropropulsion (SRP) is an often-desired configuration for maximum effectiveness of vehicle deceleration. However, the flowfields are difficult to examine due to three-dimensionality and unsteadiness is not well classified. This thesis experimentally investigates the influence of jet stagnation pressure on SRP flowfields of an inline tri-nozzle, similar to that of a Falcon 9 reentry burn configuration. A high-speed schlieren photography method capable of producing sharp and detailed image data at 76,000 Hz was used for flow visualization. Tests were conducted with jets located at the center of a perfectly expanded Mach 2 flow from a Ludwieg tube into room conditions. Comparisons are made with a range of single-jet configurations. Initial investigations corroborated earlier observations existence of a coherent bow shock oscillation unsteadiness at the equal jet and freestream stagnation pressures. The tri-nozzle SRP flowfield was observed to have an increase in directional asymmetry with increasing jet pressure. Bow shock penetration and rippling type unsteadiness were observed, similar to yet less frequent than a single nozzle with forebody, and very different from the coherent bow shock motion observed by Tan (2018). Despite two different types of unsteadiness, the maximum normalized bow shock movement was observed to be similar among all nozzle types, which suggests that similar mechanisms may underpin both types of unsteadiness.