Evaluation of force term in lattice Boltzmann method with discrete external boundary force for flow over an immersed body

In this paper, lattice Boltzmann method is used for the simulation of two-dimensional flow over an immersed solid body using external boundary force. Fluid simulation is performed using the Eulerian grid for the entire computational domain, while the domain of solid body is discretized using a boundary-fitted Lagrangian grid, imposed on the uniform Eulerian grid. Fluid–solid interaction is modeled using external boundary force (EBF) technique. Two different methods of implementing boundary force are discussed including modification in (a) collision step of LBM and (b) both collision and computation of macroscopic velocity steps. Computations are performed for flow over a stationary circular object as well as particle sedimentation. Results of drag force and sedimentation velocity show good correspondence with previously published ones at Re =1.0 for both methods. No discrepancy in results was observed between two methods for higher Reynolds numbers. Results obtained for sedimentation of an elliptical object show that the type of implementation of boundary force has no significant effect on the predicted location and angular position of the elliptical object. Furthermore, it is observed that more accurate results are obtained by introducing a modification in EBF for which solutions were independent of the number of nodes on the surface boundary.