In a previous study, the authors proposed slit injection as a jet noise suppressor for the Pre-cooled Turbojet Engine, and the noise reduction performance was examined experimentally. Using the slit injection, the noise radiation decreased. It was implied that, by using the slit injection, the instability of the jet was suppressed due to the deformation of the velocity profile of the jet. In this study, the effect of the deformation of the velocity profile of the jet by using the slit injection on the instability of the jet was investigated numerically. The velocity profiles were given by the results of a Pitot tube measurement. The stability of the jet was investigated using the linear stability analysis. The numerical results were compared with the jet noise spectra obtained experimentally. It was found that, by using the slit injection, the instability of the main jet oscillation mode, which may contribute to the noise radiation, was suppressed due to the mitigation of the steep velocity gradient of the main jet shear layer.
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