Control of High-Temperature Impinging Jet Issued from Overexpanded Rocket Nozzle

High-speed impinging jets issued from the exhaust of a launch vehicle are highly oscillatory and create hazardous conditions for the vehicle structure, affecting the sensitive payloads and personnel due to intense acoustic loads. Therefore, to reduce the unsteadiness of a jet and mitigate its adverse effects, a fundamental understanding of the associated flow and acoustic field is of utmost importance. The present experimental study is one such step to characterize the aeroacoustic properties of a high-temperature jet issued from an overexpanded rocket nozzle. Further, the effectiveness of microjet-based active flow control in reducing the flow unsteadiness and near-field noise levels is also explored. The experiments were performed at different jet stagnation temperatures, and the results were quantified at different impingement heights simulating the takeoff and landing environment of reusable launch vehicles. Mean pressure measurements were mapped on the ground plane using discrete pressure taps. The time-varying pressure component was measured using an unsteady pressure transducer located at the impingement point, and near-field acoustic measurements were carried out using a microphone. In addition, the velocity field was mapped using planar particle image velocimetry. The near-field pressure spectra are broadband, and the magnitude of noise content is a function of jet stagnation temperature. Furthermore, the injection of microjets resulted in a significant attenuation of near-field noise, impingement point pressure fluctuations, and turbulent kinetic energy.