Incipient motion of a single particle on regular substrates in laminar shear flow
Incipient motion of a single particle on regular substrates in laminar shear flow
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DOI：
10.1063/1.4753941
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发表时间：
2012-09
影响因子：
4.6
通讯作者：
J. R. Agudo;A. Wierschem
中科院分区：
文献类型：
--
作者：
J. R. Agudo;A. Wierschem
实验研究了层流条件下沉积在规则基底上的单个球形颗粒的初始运动的临界条件。基板是三角形和正方形排列的相同的玻璃球。对于后一种配置，衬底球体之间的距离是变化的，导致沉积颗粒对剪切流的不同部分屏蔽。对于所研究的颗粒雷诺数范围在3 × 10−4和3之间，临界希尔兹数与颗粒密度和颗粒雷诺数无关，但它明显取决于基底的几何形状。根据基质珠之间的间距，从而对颗粒暴露于流，我们已经观察到的临界希尔兹数增加约50%。研究颗粒运动的开始作为基板的取向的函数的流动方向，我们发现，临界希尔兹数的变化高达2倍，这主要是由于这样的事实，即颗粒通过基板的槽，因此在行进方向上的剪切力减小，如果不符合流动方向。除了临界屏蔽数，我们研究粒子运动的初始阶段，通过检测的最小时间，这是必要的保持一定的屏蔽数，以改变一个粒子的位置上的常规基板。在所研究的范围内，运动的初始阶段的尺度上的基板的周期性主要是由平衡粒子运动。
We study experimentally the critical conditions for incipient motion of a single spherical particle deposited on a regular substrate under laminar flow conditions. The substrates are triangular and quadratic arrangements of identical glass spheres. For the latter configuration, the distance between the substrate spheres is varied, resulting in different partial shielding of the deposited particle to the shear flow. For the studied particle Reynolds numbers range between 3 × 10−4 and 3, the critical Shields number is independent from the particle density and from the particle Reynolds number but it depends significantly on the geometry of the substrate. Depending on the spacing between the substrate beads and thus on the exposure of the particle to the flow, we have observed an increase of about 50 percent in the critical Shields number. Studying the onset of particle motion as a function of the orientation of the substrate to the flow direction we find that the critical Shields number changes by up to a factor of 2, which is mainly due to the fact that the particle travels through the troughs of the substrate and hence the shear force in travel direction diminishes if not in line with the flow direction. Besides the critical Shields number we study the initial stage of particle motion by detecting the minimum time that is necessary for maintaining a certain Shields number to change the position of a single particle on the regular substrates. In the range studied, the initial stage of motion on the scale of the substrate's periodicity is mainly governed by the equilibrium particle motion.