STUDY ON THE SIMULTANEOUS MEASUREMENTS OF VORTEX MOTIONS AND SOUND SOURCES

本研究揭示了与涡运动有关的声音产生机制，并提出了降低流致噪声的思路。结果总结如下：(1)对从锐边圆孔喷射的气流进行了速度和脉动静压的同时测量，讨论了旋涡声理论和膨胀理论的声源项与旋涡运动的关系。射流在相互作用模式下被激发，从而利用相位平均技术在空间和时间域上确定速度和脉动静压。这些理论的声源项是由相平均速度和波动静压通过空间和时间的微分过程得到的。结果表明，强声源是由涡旋的上升/合并和涡旋配对过程中涡旋的加速引起的。(2)压力测量预测的强声源区与涡声理论预测的强声源区相对应。结果表明，通过压力测量可以探测到强声源区域。(3)隔栅混合层传播的噪声与旋涡运动相关的声源密切相关。(4)为了降低汽车前柱与后视镜分离流的噪声，实验研究了不同涡流抑制装置对汽车前柱与后视镜分离流的抑制效果。结果表明，该装置能有效抑制声源引起的涡流运动。

The present study reveals the sound-generation mechanism in related to vortex motions, and proposes the ideas to reduce flow-induced noises. The results are summarized as follows.(1) Simultaneous measurements of velocity and fluctuating static-pressure are carried out in an air jet issuing from a sharp-edged circular orifice, and the sound-source terms of the vortex sound theory and the dilatation theory are discussed in relation to vortex motions. The jet is excited in the interaction mode so that velocity and fluctuating static-pressure can be determined in space and time domains by using phase-average technique. The sound-source terms of the theories are obtained from the phase-average velocity and fluctuating static-pressure via the differential process in space and time. The result suggests that intense sound sources are caused by the vortex rolling-up/merging and by the acceleration of vortices during vortex pairing.(2) The intense sound-source regions predicted by pressure measurements correspond to those predicted by the vortex sound theory. The result suggests that the intense sound-source regions can be detected by pressure measurements.(3) The noise propagating from the separated mixing layer from a fence is strongly correlated to the sound source related to the vortex motions.(4) In order to reduce the noise from the separated flow from the front pillar and the side mirror of an automobile, the effects of the devices to suppress vortex evolutions are investigated experimentally. The results show that the devices are very effective to suppress the vortex motions related to sound sources.