A STUDY ON NOISE GENERATION IN UNSTEADY SUPERSONIC FLOW

往复式发动机或往复式压缩机排气管内的脉动流动是复杂的，冲击波和压力波穿过阀门、喷嘴、孔板等管路元件，流动变得不充分。为了对这种流场进行实验模拟，采用了两个激波管。将连接到每个激波管的两个管子组合成一个管子，并再现上述脉动流中的一个流型循环。在不同条件下进行实验，得到详细的流动结构，采用阴影照相法和纹影法对流场进行可视化，同时测量声级。利用小波变换对测量结果进行了分析，并与可视化结果进行了比较，探讨了噪声产生的机理。采用TVD格式对流场进行了数值模拟。将实验结果与数值计算结果进行了比较，发现流场中产生的压力波是噪声源之一。

The pulsating flow in the exhaust pipe of reciprocating engine or reciprocating compressor is complicated, where shock waves and pressure waves pass through the piping elements such as valves, nozzles, orifices etc. and the flow becomes underexpanded. In order to simulate such flow field experimentally two shock tubes are used. Two pipes connected to each shock tube are combined to form a single pipe and one cycle of flow pattern in the above pulsating flow is reproduced. Thus, the experiments are conducted under various conditions and a detailed flowstructure can be obtained.The shadow photography and Schliern photography are used to visualize the flow field and at the same time the sound level is measured. The measured results are analyzed by wavelet transformation, which are compared to the visualized results, and the mechanism of the noise generation is examined. The flow field is also numerically simulated using the method known as TVD scheme. Experimental results are compared to those of numerical computation and the pressure waves generated in the flow field are found to be one of the noise sources.