STUDY ON THEREDUCTION OF AERODYNAMIC NOISE BY VORTEX CONTROL

本研究的目的是为涡流控制技术降低气动噪声提供基础材料。结果总结如下。（1）通过流动显示实验和相位平均测量研究了突片（涡流发生器）对喷流噪声的影响。研究结果揭示了涡环与流向涡的相互作用对声产生的抑制机理。特别是弄清涡环周围流向涡的切割重联机理，证实涡对的抑制作用，对工程应用具有重要意义。（2）通过测量均匀流场中方柱体的噪声，研究了起绒织物的降噪效果。结果表明，筒体上的绒面织物能有效地抑制分离流的涡运动和配对，并能降低与涡运动有关的噪声。（3）通过对速度脉动和压力脉动的测量，讨论了翼刀分离混合层的声源。结果表明，在涡旋演化区和涡旋配对区，声源强度较高。与流动显示同时检测到的传播声也表明声源与旋涡运动密切相关。（4）根据本文的研究结果和相关研究成果，提出了降低气动噪声的涡控技术，并对今后的工作提出了建议。

The objective of the present study is to obtain the basic materials for the vortex control techniques to reduce the aerodynamic noise. The results are summarized as follows.(1)The effect of tabs (vortex generators) on jet noise was investigated by flow visualization experiments and phase-average measurements. The results reveal the interaction mechanism of vortex rings and streamwise vortices to lead to the suppression of sound generation. In particular, it is very important in engineering applications to make clear the cut-and-reconnection mechanism of the streamwise vortices wound around the vortex rings and to confirm the suppression of vortex pairing.(2)The effect of pile-fabrics on reducing aerodynamic noise was investigated by measuring the noise from a square cylinder in uniform flow. The results show that the pile-fabrics on the cylinder are effective to suppress the vortex evolution and pairing of separated flow and to reduce the noise related to the vortex motions.(3)The sound source of the separated mixing layer from a fence was discussed by the measurements of velocity and pressure fluctuations. The results reveal that the sound source intensity is high in the regions of vortex evolution and pairing. The propagated sound detected simultaneously with flow visualization also suggests that the sound source is closely related to the vortex motions.(4)Based on the results of the present study and the related studies, the vortex control techniques to reduce aerodynamic noise are proposed, and the future works are suggested.