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

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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.