Acoustic generation mechanism of a supersonic jet impinging on deflectors

Numerical simulation of a supersonic jet impinging to a 45-degree-inclined flat plate is conducted to reveal the correlation between hydrodynamic structure and the acoustic field. This type of acoustic generation is of interest for lift-off acoustics of launch vehicles. Through the conditional sampling, it is clarified that acoustic wave overarching the plate shock and the 1st tail shock is an onset of the acoustic wave generated near the impingement region. This result implies that the acoustic wave generated near the impingement region is formed by the interaction of turbulent structure of the jet shear layer with the plate and the tail shock waves. Preliminary numerical study is then conducted to analyze the effect of deflector shape on the plate and the tail shock waves and resulting acoustic level of launch vehicle. It turns out that magnitude of the plate shock and acoustic level around the vehicle are attenuated by employing steeply inclined flat plate. While, a tail-shock-free deflector with 45-degree initial inclination is designed to avoid formation of the tail shocks. It is found that the tail-shock-free deflector is compact in size to redirect the jet horizontally, but the acoustic level near the vehicle is almost the same with the 45-degree-inclined flat plate. The results obtained in this study shed light on deflector design criteria based on acoustic point of view.

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