Grad's approximation for moving and stationary walls in entropic lattice Boltzmann simulations

We introduce a new generalized wall boundary condition for the entropic lattice Boltzmann method (ELBM) that is capable of handling complex flow geometries including moving walls. The Grad's ten moments approximation is employed to approximate the missing populations at the boundary nodes. The new boundary condition significantly improves accuracy, stability and sub-grid features of LBM and in particular of its entropic variant, ELBM. The proposed boundary condition is tested for a range of flows in two dimensions, including planar channel flow, Couette flow, flow past a circular cylinder and sedimenting circular particles. Further simulations involving complex geometries such as flapping wing and transversely oscillating cylinder demonstrate superior stability and accuracy of the new wall boundary condition.