Separation efficiency of a hydrodynamic separator using a 3D CFD approach Modélisation 3D multi-échelle du transport particulaire dans un séparateur hydrodynamique

The aim of this study is to investigate the use of Computational Fluid Dynamics (CFD) to predict the solid separation efficiency of a hydrodynamic separator. The numerical difficulty concerns the discretization of the geometry to simulate both the global behaviour and the local phenomena that occur nearby the screen. In this context, a CFD multiscale approach was developed: a global model (at the scale of the device) is used to visualize the hydrodynamic behaviour within the device; a local model (portion of the screen) is used to determine the local phenomena that occur nearby the screen. This approach allows us to minimize the number of cells and consequently to decrease the calculation time. The Eulerian-Lagrangian approach was used to model the particle trajectories in both models. Concerning the results, the global model shows the influence of the particles characteristics on the trapping efficiency. A high density favours the sedimentation. On the contrary, particles with small densities (1040 kg/m3) are steered by the hydrodynamic behaviour and can potentially be trapped by the separator. The use of the local model allows us to visualize the particles trajectories nearby the screen. A comparison between two types of screens (perforated plate vs. expanded metal) highlights the effects created by the shape of the screen. The turbulent kinetic energy observed near the apertures favours the ejection of the particles in this region. The results are promising about screening separation technics.