Control and Application of a Locked in Phenomenon of a Jet Screech/Self-Exited-Vibration by using a Spherical Reflector.

本研究的目的之一就是阐明射流尖叫声的产生机理。重点讨论了涡流扰动与激波的相互作用以及喷管出口附近剪切层的不稳定引起的共振机理；二是在喷管出口处设置球面反射器，控制图像噪声源的位置，消除了射流的尖叫。(1)为了识别声波的相干性，设计并搭建了一台激光束声探测器。利用纹影系统和高速摄像机对安装球面反射器后的流场变化进行了目视观测。研究发现，在安装球面反射器的情况下，激波小室结构一直保持到下游。原因是在测试…取消了声波更多的He喷管出口退出激振不稳定性，停止产生扰动。因此，扰动与激波之间的相互作用变得很弱，激波的结构不受阻碍。(3)上述观测是通过带有狭缝孔的球面反射镜进行的。缝隙孔降低了消声效果，但仍然保持了消声效果。(4)比较了球面和平板反射面的消声效果。(5)比较了球面和抛物面反射面的消声效果。(6)研究了不同反射面对球面的尺寸效应。(7)研究了不同压比下球面反射器的降噪效果，发现每种压强比对应一个合适的曲率半径。(8)在上述实验中，发现了与任何尺寸的球面反射器对应的特定压强比，其中降噪效果最好。(9)为测量球面反射器在流动中的阻力(推力损失)大小做了准备。(10)为球面反射器在管道消声器中的应用做好了准备。较少

One of the purposes of the present research is to clarify the generation mechanism of jet screech. The special issues are interaction between vortex disturbances and a shock wave and a resonance mechanism caused through instability of shear layer near to the exit of a nozzle.The next one is to control the jet screech by using a spherical reflector set at the nozzle exit that controls the location of an image noise source and cancels the jet screech.(1)In order to identify the coherence of sound waves, a laser beam sound detector has been designed and built up. Fundamental data of the performance have been obtained through current investigations.(2)Visual observation of the change in flow field by the attachment of a spherical reflector has been carried out by using a Schlieren system and a high speed video camera. It was found that the shock cell structure was kept up to downstream in case of the attachment of the spherical reflector. The reason is that cancellation of sound waves at t … More he nozzle exit quits exciting instability and stops generating disturbances. Hence the interaction between the disturbances and a shock wave becomes weak and the structure of the shock wave is not hampered.(3)The above mentioned observation has been carried out through a spherical reflector with a slit hole. The slit hole lowered the level of the noise cancellation but still held the effect.(4)Comparison of the sound cancellation effect between a spherical reflector and a flat plane reflector has been carried out.(5)Comparison of the sound cancellation effect between a spherical reflector and a parabola reflector has been carried out.(6)Sizing effect of a spherical reflector has been investigated by a variety of reflectors. It was confirmed that even a small sized spherical reflector could cancel a jet screech.(7)Noise reducing effect of spherical reflectors has been studied at various pressure ratios and it was shown that there is an appropriate radius of curvature corresponding to each pressure ratio.(8)In the above experiment, it was found that there was a special pressure ratio corresponding to any size of a spherical reflector where the noise reducing effect was highest.(9)Preparation for the measurement of magnitude of resistance (thrust loss) of a spherical reflector in flow has been done.(10)Preparation for the application of a spherical reflector to a duct silencer has been done. Less