Simulation Of Free Surface Flow Based On The Lattice Boltzmann Method

Free surface flow and multiphase flow are important phenomena in both nature and metallurgy industry. The difficulty of dealing with this moving interface problems lies in the determination of their actual position, so interface tracking or capturing have been remaining one of the main research attraction in computational fluid dynamics (CFD) past decades. In recent years, Lattice Boltzmann Method (LBM) has became a alterative way to solve fluid dynamics, in which other than solving the Navier-Stocks equations, LBM solve the mesoscopic equations with a linerlized collision operator. The mesoscopic basis and localized feature of LBM make it superior in simulation of interfaces and multiphase problem.Korner et al established and LBM-VOF (Volume of Fluid) model for simulation of liquid metal foams, the computation efficiency was greatly improved by their simple pressure boundary and interface advection scheme. Nevertheless, the accuracy of the model was not fully analyzed or tested. Luo et al published another approach biased on LBM-FT (Front-Tracking), which is proved to be second order accurate, however, existing of spurious flow and the lack of local mass conservation is the main shortcoming. In the preset work, a hybrid scheme with combine of VOF and FT was used for interface capturing, and the whole system was solved through simplifying the liquid-vapor system to one single liquid phase with a free surface flow, and applying LBM for the flow dynamics.The reason of divergent of interface grids of Korner’s model was analyzed, and the main problem occurs between the exchanges of mass of two interface cells. So Lagrange points usually used in FT method was adopted to improve the accuracy of advection between interface cells. The exchange of mass between liquid cells and interface cells are remained to be algebraic operation to remain the mass conservation of whole system.Spurious flow test was performed both on LBM-FT and LBM-VOF method, it shows that the imbalance of pressure gradient and force term during discretion is the main source of spurious flow. The surface tension was calculated biased on Lagrange points and the forcing term was merged into density and discrete together in the corresponding macroscopic equations, by which the spurious flow was eliminated in our model.The new model was tested to simulate a single bubble and multiple bubbles moving in liquid, the results shows good agreement of existing simulation results, which shows that the new model have great potencial of dealing with foam evalution simulation.