Abstract It has been suggested that by mounting the jet engines of an aircraft over the wings, the wings would act as a noise shield. In 2015, Zaman et al. (J. Fluid Mech. vol. 779 (2015) 751–775) reported the results of their experiment intended to explore the feasibility of such an engine-wing configuration. Unexpectedly, they found that tones were emitted from their scaled laboratory experiment. They identified the tones as feedback tones. Many details and characteristic features of the tone phenomenon were measured and documented in their paper. However, it was uncertain as what the feedback mechanism/path was. The purpose of this paper is to propose that the feedback closure mechanism is the upstream propagating acoustic wave modes internal to the jet. Thus, the feedback loop is believed to consist of downstream propagating Kelvin-Helmholtz instability waves of the jet flow initiated at the nozzle exit by the excitation of the upstream propagating internal acoustic waves. As the instability waves grow in amplitude when propagating downstream, they cause the jet to oscillate. The oscillatory jet impinges on the trailing edge of the plate (representing a wing). The impact leads to the emission of tones and the generation of internal upstream propagating waves. These waves are supported by the jet flow. In this way, the feedback loop is closed. In this paper, results of computed tone frequencies, based on the above described feedback loop, are compared with measurements of Zaman et al. Good agreements are found. The effects of jet Mach number on tone frequencies are considered. Again, good agreements are obtained over a range of Mach numbers. Zaman et al. reported that no tones were observed when the jet Mach number exceeded 1.06. The present theoretical analysis shows that there is no upstream propagating acoustic wave mode when the jet Mach number is higher than 1.118 (fairly close to the experimental value). Therefore, at and above this Mach number the feedback loop is broken and hence there is no interaction tone. This offers a physical explanation of the observed high Mach number cut-off phenomenon.

中文翻译：

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与机翼发动机悬置概念相关的喷气板相互作用音调

摘要 有人建议通过将飞机的喷气发动机安装在机翼上，机翼将起到隔音罩的作用。2015 年，Zaman 等人。(J. Fluid Mech. vol. 779 (2015) 751–775) 报告了他们的实验结果，旨在探索这种发动机机翼配置的可行性。出乎意料的是，他们发现音调是从他们的缩放实验室实验中发出的。他们将音调识别为反馈音。在他们的论文中测量并记录了色调现象的许多细节和特征。但是，反馈机制/路径是什么还不确定。本文的目的是提出反馈闭合机制是射流内部的上游传播声波模式。因此，反馈回路被认为由下游传播的 Kelvin-Helmholtz 不稳定波组成，喷射流在喷嘴出口处启动，由上游传播的内部声波激发。随着不稳定波在向下游传播时振幅增加，它们会导致射流振荡。振荡射流撞击板的后缘（代表机翼）。撞击导致音调的发射和内部上游传播波的产生。这些波由射流支持。这样，反馈回路就关闭了。在本文中，基于上述反馈回路的计算音调频率的结果与 Zaman 等人的测量结果进行了比较。找到了好的协议。考虑了喷气马赫数对单音频率的影响。再次，在一定范围的马赫数上获得了良好的一致性。扎曼等人。据报道，当喷气马赫数超过 1.06 时，没有观察到音调。目前的理论分析表明，当喷气马赫数高于1.118（与实验值相当接近）时，不存在上游传播的声波模式。因此，在此马赫数及以上时，反馈回路被破坏，因此没有交互音调。这为观察到的高马赫数截止现象提供了物理解释。在此马赫数及以上，反馈回路被破坏，因此没有交互音调。这为观察到的高马赫数截止现象提供了物理解释。在此马赫数及以上，反馈回路被破坏，因此没有交互音调。这为观察到的高马赫数截止现象提供了物理解释。