Supersonic impinging jets may cause many adverse ground effects, including surface erosion, nonuniform surface heat transfer, lift loss, and acoustic loading. In this study, chevron nozzles are used to suppress the noise generation of supersonic impinging jets originated from a circular convergent nozzle with the jet Mach number of 1.2. An array of microphones is used to measure the far-field acoustic fields, and a schlieren system is employed to measure the near-field flow structures. Three impinging distances are considered to examine the differences between the impinging jets and the free jet, and to assess the effect of impinging distance on the noise characteristics. Two chevron nozzles with different penetration angles are designed to investigate the potentials of chevron nozzles in controlling the supersonic-impinging-jet noise. Results show that the chevron nozzles do not alter the directivity of overall sound pressure levels, but significantly reduce the amplitude at all emission angles. The discrete tones in the impinging jets are dramatically mitigated or eliminated, and the levels of broadband noise are also significantly reduced over a wide range of frequency band, regardless of the impingement distance. The influences of chevrons on the near-field flow structures are checked with the root-mean-square values and proper orthogonal decomposition of schlieren images, which provide more evidence on the noise suppression mechanism with chevrons.

中文翻译：

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超音速V形冲击射流噪声抑制实验研究

超音速撞击射流可能会引起许多不利的地面效应，包括表面侵蚀、不均匀的表面传热、升力损失和声载荷。在本研究中，V 形喷嘴用于抑制源自圆形会聚喷嘴的超音速撞击射流的噪声产生，射流马赫数为 1.2。麦克风阵列用于测量远场声场，纹影系统用于测量近场流动结构。考虑三个撞击距离来检查撞击射流和自由射流之间的差异，并评估撞击距离对噪声特性的影响。设计了两种具有不同穿透角的 V 形喷嘴，以研究 V 形喷嘴在控制超音速冲击射流噪声方面的潜力。结果表明，V 形喷嘴不会改变整体声压级的方向性，但会显着降低所有发射角度的振幅。撞击射流中的离散音调被显着减轻或消除，并且无论撞击距离如何，宽带噪声水平在很宽的频带范围内也显着降低。通过纹影图像的均方根值和适当的正交分解来检查V形对近场流动结构的影响，这为V形的噪声抑制机制提供了更多证据。