Analytical model of jet shielding
Analytical model of jet shielding
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射流屏蔽解析模型
DOI：
10.2514/3.8135
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发表时间：
1982
期刊：
影响因子：
2.5
通讯作者：
C. Gerhold
中科院分区：
文献类型：
--
作者：
C. Gerhold
本文建立了圆柱射流对固定点声源屏蔽的解析模型。导出了估计远场接收器处的归一化声压级的指向性函数。屏蔽模型进行了比较，一个点噪声源的实验数据上的未加热的空气射流和模拟的热空气射流冲击。该模型比较有利的接收器远离射流轴的位置测量屏蔽。当接近射流轴线时，估算屏蔽的趋势与测量数据不同。对模型的改进进行了讨论。飞机产生的噪声的激励不仅包括识别飞机上的噪声源，而且还包括识别源和接收器之间的传播路径。影响噪声传播路径的众多因素之一是一个射流对另一个射流的屏蔽。由于相对于周围环境的高温和流速，屏蔽射流充当源和接收器之间的部分屏障。由此产生的噪声降低不仅影响了飞机的总体噪声水平，而且还表明了喷气发动机强化作为飞机噪声控制手段的可能性。假设平面波入射到平面上，已经解决了运动介质对声音的反射和透射问题。1 - 4射线跟踪技术已经应用于二维射流5和冷射流。6二维公式，对于圆柱形噪声源撞击在屏蔽射流上的情况，已经开发了。7本研究是以前分析的三维扩展。7开发的模型包括从一个固定的，离散的频率点源，它的局部平行流的圆柱体上的冲击发射的声场。在喷嘴下游的任何位置处，射流中的温度和速度分布是均匀的。虽然这个模型是一个理想化的双射流，它被认为是纳入了一个现实的代表性，不仅是源，而且屏蔽射流的基本要素。模型开发模型的公式化屏蔽发生的机制是声在射流和周围空气之间的边界处的反射以及射流周围的衍射。噪声源由位于（r 0，0，0）处的静止离散频率点源建模。屏蔽射流是半径为a的圆柱体，并且沿z轴沿着是无限的。温度和流速在圆柱体横截面上是均匀的。该模型如图1所示。声速势的表达式是针对两个区域编写的;区域I是射流外部，区域II是射流内部。在区域I中（流外）在区域II中（流内）
An analytical model of the shielding of a stationary point noise source by a cylindrical jet is developed. The directivity function is derived which estimates the normalized sound pressure level at a far field receiver. The shielding model is compared to experimental data for a point noise source impinging on an unheated air jet and on a simulated hot air jet. The model compares favorably to measured shielding at receiver locations away from the jet axis. The trend of the estimated shielding diverges from the measured data as the jet axis is approached. Refinement of the model is discussed. STIMATION of aircraft generated noise includes identification not only of the sources of noise on the aircraft, but also of the propagation path between the source and receiver. One of the numerous factors affecting the noise transmission path is shielding of one jet by another. The shielding jet, because of the high temperature and flow speed with respect to the immediate surroundings, acts as a partial barrier between the source and the receiver. The resultant noise reduction not only affects the overall aircraft noise level, but also indicates the possibility of jet engine in- stallation as a means of aircraft noise control. The problem of reflection and transmission of sound by a moving medium has been addressed assuming a plane wave incident on a plane surface.1"4 Ray tracing techniques have been applied to two-dimensional jets5 and cold jets.6 The two- dimensional formulation, for a cylindrical noise source impinging on the shielding jet has been developed.7 The present study is an extension to three dimensions of the previous analysis.7 The model developed consists of the sound field emitted from a stationary, discrete frequency point source, which impinges on a cylinder of locally parallel flow. The temperature and velocity profiles are uniform in the jet at any location downstream of the nozzle. While this model is an idealization of the twin jet, it is felt to incorporate the basic elements essential for a realistic representation; not only of the source, but also of the shielding jet. Model Development Formulation of the Model The mechanisms by which shielding occurs are reflection of sound at the boundary between the jet and the surrounding air and by diffraction around the jet. The noise source is modeled by a stationary discrete frequency point source located at (r0, 0,0). The shielding jet is a cylinder of radius a, and is infinite in extent along the z axis. The temperature and flow velocity are uniform across the cylinder cross section. The model is illustrated in Fig. 1. The expression for acoustic velocity potential is written for two regions; region I is outside the jet, region II is within the jet. In region I (outside the flow) In region II (inside the flow)