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首页> 外文期刊>Physics of fluids >Critical inclination for absolute/convective instability transition in inverted falling films
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Critical inclination for absolute/convective instability transition in inverted falling films

机译：倒降膜中绝对/对流不稳定性转变的临界倾角

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Liquid films flowing down the underside of inclined plates are subject to the interaction between the hydrodynamic and the Rayleigh-Taylor (R-T) instabilities causing a patterned and wavy topology at the free surface. The R-T instability results from the denser liquid film being located above a less dense ambient gas, and deforming into an array of droplets, which eventually drip if no saturation mechanism arises. Such saturation mechanism can actually be provided by a fluid motion along the inclined plate. Using a weighted integral boundary layer model, this study examines the critical inclination angle, measured from the vertical, that separates regimes of absolute and convective instability. If the instability is of absolute type, growing perturbations stay localized in space potentially leading to dripping. If the instability is of convective type, growing perturbations move downwards the inclined plate, forming waves and eventually, but not necessarily, droplets. Remarkably, there is a minimum value of the critical angle below which a regime of absolute instability cannot exist. This minimum angle decreases with viscosity: it is about 85 degrees for water, about 70 degrees for silicon oil 20 times more viscous than water, and reaches a limiting value for liquid with a viscosity larger than about 1000 times the one of water. It results that for any fluid, absolute dripping can only exist for inclination angle (taken from the vertical) larger than 57.4 degrees. Published by AIP Publishing.
机译：顺着倾斜板的底面向下流动的液膜会受到流体动力学和瑞利泰勒（Rayleigh-Taylor）（R-T）不稳定性之间的相互作用的影响，从而在自由表面上形成图案化的波浪形拓扑。 R-T不稳定性的原因是，致密的液膜位于较不稠密的环境气体上方，并变形为液滴阵列，如果不出现饱和机理，液滴最终会滴落。这种饱和机制实际上可以通过沿着倾斜板的流体运动来提供。本研究使用加权积分边界层模型，研究了从垂直方向测量的临界倾角，该临界倾角将绝对和对流不稳定状态分开。如果不稳定是绝对类型的，则不断增长的扰动会停留在空间局部，从而可能导致滴落。如果不稳定是对流类型的，则不断增加的扰动会向下移动到倾斜板上，形成波浪，最终但不一定是液滴。显着地，存在临界角的最小值，在该最小值以下不能存在绝对不稳定的状态。该最小角度随粘度而减小：对于水来说约为85度，对于硅油来说约为70度，是水的20倍，对于粘度大于水的1000倍的液体达到极限值。结果表明，对于任何流体，仅当倾斜角（从垂直方向获取）大于57.4度时，才可能存在绝对滴落。由AIP Publishing发布。

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