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

本研究的目的之一是阐明射流啸叫的产生机理。特殊的问题是涡流扰动与激波的相互作用以及喷管出口附近剪切层不稳定引起的共振机制。下一个是通过在喷嘴出口使用球形反射器来控制喷射尖叫，该反射器控制图像噪声源的位置并消除喷射尖叫。(1)为了识别声波的相干性，设计并制作了一种激光束声探测器。通过目前的调查，已经获得了性能的基本数据。(2)利用纹影系统和高速摄像机对附着球面反射镜的流场变化进行了目视观察。研究发现，在安装球面反射镜的情况下，减震室结构保持在下游。其原因是在喷嘴出口处声波的消除，使得喷嘴出口处的不稳定不再产生干扰。因此，扰动与激波之间的相互作用变弱，激波的结构不受阻碍。(3)上述观测是通过带狭孔的球面反射镜进行的。狭缝孔降低了噪声消除的水平，但仍然保持了效果。(4)对球面反射器与平面反射器的消声效果进行了比较。(5)对球面反射镜和抛物线反射镜的消声效果进行了比较。(6)用不同的反射器研究了球面反射器的尺寸效应。经证实，即使是一个小尺寸的球形反射器也可以消除喷射声。(7)研究了不同压比下球面反射器的降噪效果，发现不同压比下球面反射器有一个合适的曲率半径。(8)在上述实验中，我们发现对于任何尺寸的球面反射镜，都有一个特殊的压比，在这个压比下，降噪效果是最高的。(9)为测量球面反射器在流动中的阻力（推力损失）大小做了准备工作。将球形反射器应用于管道消声器的准备工作已经完成。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