Experimental Characterization and Control of an Impinging Jet Issued from a Rocket Nozzle

Abstract

Rocket takeoff and landings result in high structural loads on the launch surface and the rocket components along with elevated noise levels. This article presents an experimental study of a jet issued from an axisymmetric Mach 4 converging-diverging nozzle operating at highly over-expanded conditions and impinging on a flat surface, representing rocket takeoff and landing conditions. Shadowgraph technique was used to visualize the flowfield to gain insight into the qualitative behavior of the jet. Mean and unsteady pressure measurements on the impinging surface were carried out to study the associated flow physics. Nearfield acoustic measurements were conducted to understand the relationship between the fluid flow and the acoustic field. Microjet-based flow control was employed to suppress flow unsteadiness and reduce noise levels. The results show that both pressure loading on the impingement surface and nearfield noise are strongly dependent on the nozzle pressure ratio. The pressure and acoustic spectra measured at various locations are broadband without any discrete tones. The use of microjets results in a fuller and more stable jet at the nozzle exit and shows a dramatic reduction in the unsteady loads on the impingement surface and overall sound pressure levels.