A Hybrid Near-wall Model for Kinetic Simulation of Turbulent Boundary Layer Flows

Turbulent boundary layer represents one of the most complex but interesting phenomena in fluid flows. While the generation and alteration of sheared vortices in various interacting scales near the boundary are visually appealing, it is difficult to correctly replicate such phenomena by simulation, especially at high Reynolds numbers. Practical methodologies typically incorporate empirical wall modeling to substantially curtail the computational expenses while retaining physical consistency. Nevertheless, these are predominantly applicable to steady-state flow solvers. While complex scenarios involving dynamic fluid-solid interaction and its application to create time-dependent flow phenomena invariably necessitate unsteady flow solvers, the underlying wall modeling techniques are imprecise, leading to a different formation of near-wall vortices, especially for the highly efficient lattice Boltzmann solver operating on Cartesian grids. In this paper, we propose a novel hybrid near-wall model for the lattice Boltzmann solver, which can handle turbulent boundary layer flows in a simple and efficient manner, inspired by measuring the degree of boundary layer separation. Our model comprises both macroscopic and mesoscopic algebraic models, which collaborate to let the low dissipation lattice Boltzmann solver naturally form the turbulent boundary layer appropriately. By leveraging the multi-resolution technique, accurate simulation outcomes can be obtained. Our model is parameterized to approximate different physical attributes of the solid surface that can potentially influence the boundary layer distribution, and comparable boundary layer flow behaviors can be simulated at various grid resolutions. Rigorous benchmark tests are carried out to validate our model at different grid resolutions by comparing with experimental data and visualizations. We showcase the applications of our new model in both facilitating computational design and generating visual animations, accompanied by specific examples and comparisons with actual experimental setups and photographic images. All demonstrations affirm the physical consistency of our solver even when simulated with a relatively coarse grid resolution.