Mechanism-Resolved Interface Momentum Transfer in Immersed-Boundary Lattice Boltzmann Simulations

Abstract

Immersed-boundary lattice Boltzmann (IB-LBM) simulations of cylinder and particle flows are usually compared by ranking boundary-enforcement schemes, kernels, and collision models. Such comparisons can obscure the mechanism that controls each response. Here, canonical fixed-cylinder, oscillating-cylinder, and sedimenting-particle cases are used as controlled probes of Eulerian-Lagrangian interface momentum transfer. For prescribed bodies, differences among direct forcing (DF), multi-direct forcing (MDF), and distribution-function correction (DFC) are most clearly discriminated by local no-slip fidelity rather than by a universal drag ranking. For DFC, the kernel-dependent drag-coefficient ranking reversal between the hat and Peskin 4-point kernels is associated with the spatial redistribution of the marker-resolved correction and the resulting near-boundary slip and pressure deviation, rather than the total correction magnitude alone. For sedimenting particles, single-particle settling provides a moving-body baseline, whereas two-particle differential-density wake-interaction sedimentation shows the wake-exposed light particle to be comparatively more sensitive to the explicit internal-mass correction in the force evaluation, a configuration-dependent, finite-window moving-boundary closure response. Targeted two-relaxation-time (TRT) and central-moment multiple-relaxation-time (CM-MRT) collision controls remain secondary to the boundary and closure mechanisms within the tested regimes (prescribed-body comparisons at Re <= 200, two-dimensional, and the reported moving-particle cases). The resulting picture replaces a universal scheme ranking with a mechanism-resolved interpretation of IB-LBM interface momentum transfer.