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arXiv 1302.0646physics.flu-dynastro-ph.EPphysics.ao-ph
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温度分层turbulence中小颗粒的缠结团簇不稳定性

Tangling clustering instability for small particles in temperature stratified turbulence

Tov Elperin, Nathan Kleeorin, Michael Liberman, Igor Rogachevskii

备注：
13 pages, 7 figures, REVTEX4-1, revised version
发表信息：
Physics of Fluids 25, 085104 (2013)
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摘要：

我们研究了有限相关时间较小的温度分层湍流中的颗粒聚集。结果表明，温度分层湍流强烈地增加了颗粒速度场的可压缩程度。这导致即使对于小颗粒，缠结聚集不稳定性的激发阈值也大大降低。温度层结湍流中的缠结团簇不稳定性与非层结各向同性和均匀湍流中的惯性团簇不稳定性有着本质的区别。惯性团簇不稳定性是由湍流涡旋的离心作用引起的，而缠结团簇不稳定性的机制则与速度脉动对平均温度梯度的缠结所产生的温度脉动有关。温度波动产生压力波动，并在压力波动增加的区域引起颗粒聚集。结果表明，纠缠团簇不稳定性的增长率远大于惯性团簇不稳定性的增长率。结果发现，依赖于参数的湍流和平均温度梯度有一个优先的颗粒尺寸，在该颗粒聚集由于缠结集群不稳定性是更有效的。在这种不稳定性饱和后，团簇内的粒子数密度可以比平均粒子数密度大几个数量级。它还表明，液滴的蒸发急剧改变缠结集群的不稳定性，例如，它增加了液滴半径的不稳定性阈值。缠结成簇不稳定性是非常重要的，例如，大气湍流和逆温现象。

英文摘要：

We study particle clustering in a temperature stratified turbulence with small finite correlation time. It is shown that the temperature stratified turbulence strongly increases the degree of compressibility of particle velocity field. This results in the strong decrease of the threshold for the excitation of the tangling clustering instability even for small particles. The tangling clustering instability in the temperature stratified turbulence is essentially different from the inertial clustering instability that occurs in non-stratified isotropic and homogeneous turbulence. While the inertial clustering instability is caused by the centrifugal effect of the turbulent eddies, the mechanism of the tangling clustering instability is related to the temperature fluctuations generated by the tangling of the mean temperature gradient by the velocity fluctuations. Temperature fluctuations produce pressure fluctuations and cause particle clustering in regions with increased pressure fluctuations. It is shown that the growth rate of the tangling clustering instability is much larger than that of the inertial clustering instability. It is found that depending on the parameters of the turbulence and the mean temperature gradient there is a preferential particle size at which the particle clustering due to the tangling clustering instability is more effective. The particle number density inside the cluster after the saturation of this instability can be in several orders of magnitude larger than the mean particle number density. It is also demonstrated that the evaporation of droplets drastically change the tangling clustering instability, e.g., it increases the instability threshold in the droplet radius. The tangling clustering instability is of a great importance, e.g., in atmospheric turbulence with temperature inversions.

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