Abstract The fluid insert technology is an active noise reduction technique that has been shown to successfully reduce supersonic jet noise in model scale nozzles. The goal of this paper is to better understand the noise reduction mechanisms of fluid insert jets using Doak's Momentum Potential Theory and Spectral Proper Orthogonal Decomposition applied to an LES database. It is found that the use of fluid inserts results in a lower convection speed of the wavepacket-like coherent structures in the jet shear layer resulting in a shallower Mach wave radiation angle. It is also shown that the use of fluid inserts results in a reduction of length scales of the turbulent fluctuations in the shear layer, which correlates correctly with the observed noise reductions.

中文翻译：

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带流体嵌件的射流降噪机理研究

摘要 流体插入技术是一种主动降噪技术，已被证明可以成功降低模型尺寸喷嘴中的超音速喷射噪声。本文的目标是使用应用于 LES 数据库的 Doak 动量势理论和光谱适当正交分解更好地了解流体插入射流的降噪机制。发现使用流体插入物导致射流剪切层中波包状相干结构的对流速度较低，从而导致马赫波辐射角较浅。还表明，流体插入物的使用导致剪切层中湍流波动的长度尺度的减少，这与观察到的噪声减少正确相关。