A note on the stochastic nature of particle cohesive force and implications to threshold friction velocity for aerodynamic dust entrainment
A note on the stochastic nature of particle cohesive force and implications to threshold friction velocity for aerodynamic dust entrainment
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DOI：
10.1016/j.aeolia.2016.08.004
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发表时间：
2016-09-01
期刊：
影响因子：
3.3
通讯作者：
Klose, Martina
中科院分区：
文献类型：
--
作者：
Shao, Yaping;Klose, Martina
确定地球和火星上风沙排放的阈值是相当有意义的。现有的阈值摩擦速度格式本质上都是确定性的，但观测表明，在粉尘粒径范围内，由于随机颗粒间粘聚，阈值摩擦速度散射强烈。在现实世界中，总是存在一定量的自由尘埃，这些尘埃很容易被弱风甚至湍流从地面带走，例如尘卷风。在降尘研究界已经提出，降尘中心的压降可能是降尘释放的主要机制，称为zip效应。这里的问题是拉链效应是实质性的，还是尘卷风中粉尘浓度的升高是由于自由粉尘的排放。简单的分析表明，压缩效应很小，尘卷中的粉尘可能是由于自由粉尘排放和粉尘辐合造成的。为了估计自由粉尘释放量，有必要确定粉尘颗粒阈值摩擦速度的下限。通过对粒子间内聚力的中值和方差的假设，给出了该速度的一个简单表达式。该简单表达式拟合了亚利桑那州立大学涡发生器的数据。虽然该方案仍有相当大的不确定性，但本说明强调需要对粉尘排放的随机性进行进一步研究。(C) 2016年Elsevier B.V.出版
There is considerable interest to determine the threshold for aeolian dust emission on Earth and Mars. Existing schemes for threshold friction velocity are all deterministic in nature, but observations show that in the dust particle size range the threshold friction velocity scatters strongly due to stochastic inter-particle cohesion. In the real world, there always exists a certain amount of free dust which can be easily lifted from the surface by weak winds or even turbulence, as exemplified by dust devils. It has been proposed in the dust-devil research community, that the pressure drop at dust-devil center may be a major mechanism for dust-devil dust emission, known as the zip effect. It is questioned here whether the zip effect is substantial or whether the elevated dust concentration in dust devils is due to free dust emission. A simple analysis indicates that the zip effect appears to be small and the dust in dust devils is probably due to free dust emission and dust convergence. To estimate free dust emission, it is useful to define a lower limit of dust-particle threshold friction velocity. A simple expression for this velocity is proposed by making assumptions to the median and variance of inter-particle cohesive force. The simple expression is fitted to the data of the Arizona State University Vortex Generator. While considerable uncertainty remains in the scheme, this note highlights the need for additional research on the stochastic nature of dust emission. (C) 2016 Published by Elsevier B.V.