Two pressure boundary conditions for multi-component multiphase flow simulations using the pseudo-potential lattice Boltzmann model

In this study, two boundary condition (BC) schemes are proposed for the pseudo-potential (PP) lattice Boltzmann method (LBM). The two BC schemes include a modified Convective Boundary Condition (mCBC) and a modified Non-equilibrium Bounceback (mNEBB), and their development is aimed at treating pressure-driven outflow problems for fluids with similar and different density ratios in multi-component multiphase (MCMP) environments. It is the first attempt to incorporate interaction force at boundaries for MCMP fluids. Key limitations of existing LBM boundary schemes for MCMP flow are alleviated. In particular, the constraint of zero-velocity specification at tangential direction is removed by applying the proposed mCBC scheme. In addition, it is demonstrated that multiphase outflow performance is improved with the application of either scheme, while alleviating the nonphysical distortions introduced by the available BC schemes. Three numerical case studies have been conducted to test the proposed scheme. Results have been validated using uncut-off extended domains. These cases are designed to test the induced distortion to the fluids exiting boundaries, examine the scheme’s capability to treat the pressure boundary condition, and explore whether the model can make physically meaningful predictions when these modified BCs are applied. The mCBC scheme is shown to be more capable to correctly treat such pressure specified boundary conditions.