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首页> 外文期刊>Experimental Thermal and Fluid Science: International Journal of Experimental Heat Transfer, Thermodynamics, and Fluid Mechanics >Experimental study of transition to turbulence of a round thermal plume by ultrasound scattering
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Experimental study of transition to turbulence of a round thermal plume by ultrasound scattering

机译：超声散射法研究圆形热羽向湍流过渡的实验研究

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In this study, we carried out the characterization of the transition to turbulence of a thermal pure plume by using ultrasound scattering. For this, the position, amplitude and broadening of the scattering peak are analyzed. The technique is based upon the scattering of an ultrasound wave coupling with an unstable how. The coupling between the acoustic mode with both vorticity and entropy modes is derived from non-linear terms of Navier-Stokes and energy equations. When the scattering mechanism occurs, the characteristic length scale of the flow structure under observation is comparable with the wavelength of incoming sound. Thus, the flow can be probed at different length scales by only changing the frequency of incoming sound. The thermal plume rises from a heated disk immersed into a quiescent medium and can reach transition and fully turbulent regimes. Criteria allowing the identification of both the beginning and the end of transition are derived from the results. The characteristics of the scattering process show evidence that allows us to discern the beginning of transition. The analysis of the amplitude of the scattering peak revealed a homogeneous behavior and led us to think of a possible principle of similarity. The evolution of both thermal and velocity fluctuations has made it possible to establish the limits of both the beginning and the end of transition, in terms of local Grashof number Gr(z) and position of the measurement zone z/D. The limits for transition reported in this work are comparable in its magnitude order with those of the literature. It was verified that thermal and velocity transition are phenomena that begin and finish almost simultaneously. (C) 2000 Elsevier Science Inc. All rights reserved. [References: 36]
机译：在这项研究中，我们通过使用超声散射对热羽流向湍流的过渡进行了表征。为此，分析了散射峰的位置，幅度和展宽。该技术基于具有不稳定方式的超声波耦合的散射。声学模式与涡度模式和熵模式之间的耦合是从Navier-Stokes和能量方程的非线性项导出的。当发生散射机制时，观察到的流动结构的特征长度尺度与入射声音的波长相当。因此，仅改变输入声音的频率就可以在不同的长度范围内探测气流。热羽从浸没在静态介质中的加热盘上升而来，可以达到过渡态和完全湍流态。从结果中得出可以识别过渡开始和结束的标准。散射过程的特征表明，有证据使我们能够辨别转变的开始。散射峰幅度的分析显示出均匀的行为，使我们想到了相似性的可能原理。热和速度波动的演变使得可以根据局部Grashof数Gr（z）和测量区域z / D的位置来确定过渡开始和结束的极限。在这项工作中报道的过渡极限在数量级上与文献中的相当。证实热和速度转变是几乎同时开始和结束的现象。 （C）2000 Elsevier Science Inc.保留所有权利。 [参考：36]

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