A Study On Stability And Sound Radiation Of Supersonic Compressible Mixing Layer

The noise problem caused by pulse exists in the aviation and natural industry. It has seriously affected people's life. Accurately understanding the dynamic of the flow is fundament to researching the noise of mixing layer, so researching the relationship, between the near field dynamics characteristics of instability wave and far field sound radiation, has important significance for understanding, predicting and controlling the noise. At the present, two-dimensional nonlinear disturbance equation and convective wave equation are used to research the relationship, the basic flow is got by Blasius solution, the supersonic compressible mixing layer is as the research object, discussing the relationship between near field dynamics and the far field sound radiation for supersonic mixing layer.The results are concluded and listed below:Mach 2.5/1.5 supersonic mixing layer1. The most unstable growth wave is forced to the inlet, large scale vortex structure was found during the evolution process of the disturbance, with vortex structure evolution to downstream, perturbation pressure radiates to the far field directly, sound radiation mechanism is mainly caused by the nonlinear vortex structure.2. A pair of three-dimensional perturbations wave are forced to the inlet, the vortex structure is stretched, finally broken, becoming many small vortices, at the same time, the perturbation pressure radiates to the far field.Mach 4.0/1.6 supersonic mixing layer.3. The disturbance exists multi modes, the same frequency0? is corresponding to the two growth radiosi-?, namely fast mode and slow mode. The evolution of two disturbance modes are computed, vortex structure was not found in near field,the pressure which disturbance is supersonic relatives to the free flow velocity radiates the free flow field in Mach wave form, the Mach angle is consistent with the theoretical value.4. Near field pressure is calculate by disturbance equation shows the envelope curves of Mach wave in near field are a cluster of parallel lines, the envelopes of Mach wave in far field calculated by Wu's Integration are no longer a cluster of parallel lines, acoustic wave has obvious diffraction.In conclusion, when the convective Mach number of supersonic mixing layer is less than 1, the sound radiation mechanism is caused by the large scale vortex structure. The intensity of the far field radiation is enhanced by nonlinear interaction.Meanwhile when the convective Mach number of supersonic mixing layer is more than 1, the sound radiation mechanism is in the form of Mach wave. The envelope curves of the far field Mach wave are no longer a cluster of parallel lines. The acoustic wave has obvious diffraction.