Computational model for the simulation of the windblown sand transport, sedimentation, erosion and avalanching around obstacles

Windblown sand transport, accumulation and erosion around structures and infrastructures in arid regions poses significant threats about their safety and serviceability. The mathematical modeling of the above phenomena is a challenging task, because of the interaction between the multiple phases of wind and sand, the time-dependent free interface among them, the multiple scales from km-long infrastructures to mm-sized sand grains through the turbulent wind energy cascade. The accurate and efficient computational simulation of the above phenomena is of paramount scientific and industrial importance, because of the lack of similarity in scale wind tunnel tests and of the costs and uncertainties in full scale field tests. The present MSc thesis aims at tackling the above issues. A coupled multiphase mathematical model is adopted in the framework of continuum mechanics and discretized by adopting the Finite Volume and Immersed Boundary methods. The resulting computational model is implemented in the open source OpenFOAM code. The MSc Thesis takes advantage of the computational approach to evaluate the sensitivity of the solution to several model physical parameters (e.g. the sand diameter and related threshold shear velocity, the sand angle of repose) and components of the mathematical model. In particular, two different semi-empirical sand drift models are adopted and the three main sand transport terms in the modified Exner equation (i.e. Erosion, Deposition, Avalanching) are alternatively switched on/off. The developed approach is applied to the benchmark of the high-Reynolds wind and windblown sand flow around a bluff body immersed in the atmospheric boundary layer, namely a wall-mounted cube. The huge amount of previous experimental measurements and high-fidelity computational simulations of the wind flow around such a setup allows to properly compare the obtained aerodynamic results. A single but fairly well-documented experimental and computational study about windblown sand dynamics is a useful initial reference for the multiphase simulation. The Thesis has been developed in the framework of the Windblown Sand Modelling and Mitigation joint Research and Development Group established between the Departments of Mathematics and Architecture and Design at Politecnico di Torino and Optiflow Company (Marseille, France). The Optiflow Company has hosted the MSc candidate during a 6 months stage at its facilities in Marseille.