Study on Aerodynamic Noise induced by Shock Waves in Supersonic Flows and Development of a Method for Reducing the Noise

1.利用超声速风洞研究了超声速喷管和超声速扩压器内正激波的振荡现象，发现激波振荡、壁面静压脉动和产生的气动噪声之间有很强的相关性.小的压力扰动的产生和传播上游的冲击波的下游部分进行了观察，并发现，这些扰动引起的冲击振荡。在下游部分，边界层的行为不稳定和激烈。此外，由激波振荡产生的涡流被观察到对流下游。基于这些结果，我们解释了激波振荡是由上游传播的扰动和下游对流涡维持的.分析了超声速扩压器中正激波对具有相同功率谱密度的白色小压力扰动的响应，得到的激波位移谱密度分布与实验测量值吻合得很好.对正确膨胀和欠膨胀超音速层流和湍流射流的结构进行了理论和实验研究，明确了射流中枢轴冲击压力和流动湍流度的分布、势核长度、激波的产生条件和位置.解释了皮托管冲击压力沿着射流中心线分布的流动机理，以及正确膨胀和欠膨胀的超声速射流与气动噪声的关系。

1. The oscillations of the normal shock waves in supersonic nozzles and supersonic diffusers were investigated using a supersonic wind tunnels, and a strong correlation were found among the shock oscillation, the static pressure fluctuation on the wall, and the generated aerodynamic noise.2. Small pressure disturbances which are generated and propagated upstream from downstream portion of the shock wave were observed, and it was found that these disturbances induce the shock oscillation. At the downstream portion, the boundary layer behaves unsteadily and violently. Also, vortices generated by the shock oscillation were observed to be convected downstream. Based on these results, the shock oscillation was explained to be sustained by the upstream-propagating disturbances and the downstream-convected vortices.3. The response of a normal shock wave to a white small pressure disturbance having the same power spectral density in the supersonic diffuses was analyzed, and it was shown that the shock displacement spectral density distributions obtained by the analysis agree very well with those measured in the present and previous experimental data.4. Theoretical and experimental investigations were performed on the structures of correctly-expanded and under-expanded supersonic laminar and turbulent jets, and the distributions of the Pivot impact pressure and flow turbulence in the jets, the length of the potential core, the condition of the generation of shock waves and their locations in the jets were made clear.5. The flow mechanism on the distributions of the Pitot impact pressure along the center line of the jet was well explained, and the correlation between the aerodynamic noise level and the correctly and under expanded supersonic jets.