Particle-based simulation of Aeolian transport: Granular electrification controls on the initiation of particle motion

本研究方案的总体目标是开发一种离散单元法（DEM），用于模拟风成沙的输送和粉尘气溶胶颗粒向大气中的级联排放。这一模拟将有助于改善气候模型中尘埃循环的表现，并对广泛的应用具有根本意义，包括沿海管理、行星科学和荒漠化研究。在该项目的第一阶段，我们实现了一个数值工具，耦合流体力学模型的湍流风场在大气边界层与颗粒动力学，考虑颗粒间的接触和货车范德华力。在该项目的下一阶段，该DEM模拟将被扩展以纳入接触带电（摩擦充电）过程产生的颗粒间静电相互作用的影响。 沙尘暴伴随着几kV/m到几百kV/m的电场。这样的电场可以显着降低风成土颗粒（Ut）的直接气动夹带的最小阈值风切变速度，从而有助于提高沙的传输，沙丘迁移和粉尘排放率显着。然而，预测Ut在电荷的存在下是具有挑战性的，因为它仍然是知之甚少的颗粒之间的静电相互作用在土壤中的影响的微观（颗粒尺度）的动力学的风成沉积物床。这些微观动力学及其对UT的作用将构成下一个项目阶段的研究主题，使用我们的DEM模拟。最近在杜伊斯堡-埃森大学物理系进行了风洞实验，以估计颗粒尺寸和电荷的特定分布的Ut。这些实验的数据将有助于验证我们的模型。这里提出的研究将铺平道路的DEM表示颗粒材料的摩擦充电-一种现象的基本相关的许多领域的环境和工程科学。

The overall goal of the present research programme is the development of a Discrete-Element-Method (DEM) for the particle-based simulation of Aeolian sand transport and the concatenated emission of dust aerosol particles to the atmosphere. This simulation will contribute to improving the representation of the dust cycle in climate models and is of fundamental relevance to a broad range of applications, including the coastal management, the planetary sciences and the desertification research. In the first phase of this project, we achieved a numerical tool that couples a fluid mechanics model for the turbulent wind field in the atmospheric boundary layer with granular dynamics, by considering interparticle contact and van der Waals forces. In the next phase of the project, this DEM simulation will be extended to incorporate the effect of particle-particle electrostatic interactions resulting from contact electrification (tribocharging) processes. Sand and dust storms are accompanied by electric fields of a few kV/m to several hundred kV/m. Such E-fields may significantly reduce the minimal threshold wind shear velocity for direct aerodynamic entrainment of Aeolian soil particles (Ut), thereby contributing to enhance sand transport, dune migration and dust emission rates substantially. However, predicting Ut in the presence of electric charges is challenging because it is still poorly understood how electrostatic interactions between grains in the soil affect the microscopic (particle-scale) dynamics of Aeolian sediment beds. These microscopic dynamics and their role for Ut will constitute the topic of research in the next project phase, using our DEM simulations. Wind tunnel experiments have been conducted recently at the Faculty of Physics of the University of Duisburg-Essen to estimate Ut for specific distributions of particle size and electric charges. The data from these experiments will be helpful, thus, for the validation of our model. The research proposed here will pave the way for a DEM representation of tribocharging in granular materials – a phenomenon of fundamental relevance to many areas of environmental and engineering sciences.