Experimental investigation of density fluctuations in high-speed jets and correlation with generated noise
Experimental investigation of density fluctuations in high-speed jets and correlation with generated noise
复制标题
高速射流密度波动及其与产生噪声的相关性的实验研究
DOI：
10.1017/s002211200100622x
复制
发表时间：
2002
影响因子：
3.7
通讯作者：
R. Seasholtz
中科院分区：
文献类型：
--
作者：
J. Panda;R. Seasholtz
用基于瑞利散射的方法实验研究了完全膨胀的、未加热的自由喷流羽流中的空气密度波动。该点测量技术使用了连续波激光、光纤传输和光子计数电子学。时间平均密度和均方根密度起伏的径向和中心线分布提供了对喷流增长的对比描述。采用双光电倍增管(PMT)技术测量密度涨落光谱。两个PMT信号之间的互相关显著降低了电子散粒噪声的贡献。所有马赫数喷流的密度涨落谱都非常相似。对马赫数为0.95、1.4和1.8的完全展开喷流进行的详细调查进一步证实，除了马赫数增加的空间伸展外，各种斯特劳哈尔频率起伏的分布仍然相似。尽管流量波动相似，但这三种射流中的噪声源被发现有很大的不同。火花纹影照片和近场麦克风测量证实，马赫1.8喷流中存在马赫波辐射，而0.95马赫喷流中没有马赫波辐射。流密度起伏(起因)和远场声压起伏(效应)之间的直接相关测量进一步揭示了声的产生过程。为此，麦克风被固定在一个远场点，主要是在与流动方向50直径和30°的距离处，并且激光探头体积在流动中从一个点移动到另一个点。在马赫数为1.8的急流中，当Kelvin-Helmholtz不稳定波的对流速度超过环境声速时，从周边剪切层测量到了显著的相关性，而在马赫数为0.95的不稳定波具有亚音速对流速度的情况下，没有测量到相关性。虽然马赫数为1.8和0.95的喷流中都存在相同的不稳定波，但前者的周边剪切层是一个明显的噪声源，而后者则不是。沿喷流中心线的进一步相关研究表明，在所有被测试的马赫数喷流中，势核下游区域的行为相似，为0：6[LES]M[LES]1：8。在低Strouhal频率下，从该区域测量到良好的相关性，该区域从势核下游开始，从那里延伸了许多直径。
The air density fluctuations in the plumes of fully expanded, unheated free jets were investigated experimentally using a Rayleigh-scattering-based technique. The point measuring technique used a continuous-wave laser, fibre-optic transmission and photon counting electronics. The radial and centreline profiles of time-averaged density and root-mean-square density fluctuation provided a comparative description of jet growth. To measure density fluctuation spectra a two-photomultiplier-tube (PMT) technique was used. Cross-correlation between the two PMT signals significantly reduced the electronic shot noise contribution. The density fluctuation spectra were found to be remarkably similar for all Mach number jets. A detailed survey in fully expanded Mach 0.95, 1.4 and 1.8 jets further confirmed that the distribution of various Strouhal frequency fluctuations remained similar, except for a spatial stretching with increased Mach number. In spite of this similarity in flow fluctuations the noise sources in these three jets were found to be significantly different. Spark schlieren photographs and near-field microphone measurements confirmed that Mach wave radiation was present in the Mach 1.8 jet, and was absent in the Mach 0.95 jet. Direct correlation measurement between the flow density fluctuation (cause) and far-field sound pressure fluctuation (effect) shed further light on the sound generation process. For this purpose a microphone was kept fixed at a far-field point, mostly at a distance of 50 diameters and 30° to the flow direction, and the laser probe volume was moved from point to point in the flow. In the Mach 1.8 jet, where the convective velocity of Kelvin–Helmholtz instability waves exceeded the ambient sound speed, significant correlation was measured from the peripheral shear layer, while in the Mach 0.95 jet, where the instability waves had subsonic convective speed, no correlation could be measured. Although the same instability waves were present in both Mach 1.8 and 0.95 jets, the peripheral shear layer of the former was found to be an obvious noise source, while that of the latter was not. Further correlation studies along the jet centreline showed that behaviour in the region downstream of the potential core was similar in all Mach number jets tested, 0:6[les ]M[les ]1:8. Good correlation at low Strouhal frequencies was measured from this region, which started from downstream of the potential core and extended many diameters from there.