Substrate impact on flow induced particle motion in laminar shear flow

流动诱导固体颗粒在固定基质或颗粒床上的分离和运动在许多自然和工业系统中具有重要意义。作为例子，可以提到过滤、天然水道和管道系统中的泥沙和颗粒输送、呼吸系统中的颗粒输送以及表面的清洁。在微流体中，球形颗粒逐渐被用作信息载体或阀门或泵等执行器。因此，一个重要的前提是颗粒的可控定位。虽然人们很好地理解了单个颗粒在光滑壁上的运动，但这并不适用于结构表面和颗粒床。尽管关于粒子运动的开始、运动本身，或者更确切地说，关于物质传输的许多研究，这些重要的技术过程仍然没有得到很好的描述。这是因为颗粒去除只针对无序的沉积层进行了研究，并试图在现有模型中使用定义不明确的参数来描述。由于忽略了精确的颗粒排列，基片几何形状、暴露在流动中和相邻颗粒的阴影的影响仍然不清楚。因此，基质几何形状和相邻颗粒对颗粒运动开始和沿基质本身运动的影响尚不清楚。颗粒床通过两种方式阻碍颗粒运动：一方面，不平坦的基质构成障碍，必须克服下游接触角；另一方面，颗粒遮挡了颗粒的流动。以类似的方式，邻近的粒子起到额外的阻碍作用。从这个观察开始，我们计划改变相关参数。该项目的目的是在没有明确定义的参数的情况下，在一个模型中定量地描述层流剪切流动中颗粒运动的开始和沿衬底本身的运动。

Flow induced detachment and motion of solid particles on a fixed substrate or granular bed is of fundamental relevance in numerous natural and industrial systems. As examples sediment and granular transport in filtration, natural watercourses and piping systems, particle transport in the respiratory system, and the cleaning of surfaces may be mentioned. In microfluidics, spherical particles are progressively used as information carrier or for actuators like valves or pumps. Therefore, an important precondition is the controlled positioning of particles. While the motion of single particles on smooth walls is quite well understood, this does not hold for structured surfaces and granular beds. Despite numerous studies concerning the onset of particle motion, the motion itself or rather the material transport, these technologically important processes are still not well described. This is due to the fact that particle removal has been studied exclusively for disordered sediment layers and has been tried to describe using not well-defined parameters in the existing models. Since the precise particle arrangement is ignored, the effects of substrate geometry, exposure to the flow and shading by neighboring particles remains unclear. Hence, the impact of substrate geometry and of neighboring particles on the onset of particle motion and the motion along the substrate itself remains unclear.Granular beds hinder particle motion in two ways: On the one hand, the uneven substrate poses an obstacle, which downstream contact angle has to be overcome, on the other hand, its shades the particle against the flow. In an analogue manner, neighboring particles serve as an additional hindrance. Starting from this observation, we plan to vary the relevant parameters. The aim of the project is to describe the onset of particle motion and the motion along the substrate itself in laminar shear flows quantitatively in a model without recourse to not well-defined parameters.