Acoustic Radiation Model for Clustered Rockets Using Low-density Gas Jets

In this study, a model based on reflection, refraction, and diffraction of sound waves is developed for the two jets placed in parallel to predict the acoustic fields of clustered hybrid rocket. Furthermore, the spreading of the jets and the integration of jets are considered in the model. In the experiments using a low-density gas jet that simulates the high-temperature, high-speed jet of a hybrid rocket, noise from two jets is measured and the flow field in the vicinity of the jets were visualized with schlieren method with various nozzle spacings. Jet visualization results show that the jet spread angle is 15deg. The acquired acoustic data and the predictions by the acoustic radiation model were compared. The model predicted radiation angle characteristics at each azimuthal angle and nozzle spacing within the error of ±1dB. It is necessary to consider sound wave reflection, refraction, and diffraction and the integration of the jets to predict the acoustic radiation characteristics of a clustered hybrid rocket.