Estimating the distribution functions for emerging nodes which transition from the solid phase to the fluid phase during boundary movement remains a critical challenge in the lattice Boltzmann method. This paper proposes an improved treatment for these nodes by implementing virtual fluid and virtual boundary conditions for the distribution functions on solid nodes adjacent to the solid-fluid boundary. To validate the effectiveness of the proposed method, two-dimensional simulations of flow around a circular cylinder and a square cylinder, both subject to forced cross-stream oscillation, were conducted and compared against conventional approaches. The results indicate that the proposed method significantly suppresses spurious force oscillations in fluid forces compared to conventional methods. These spikes originate from discontinuities in local forces at emerging fluid nodes and the proposed method proved to be extremely effective in mitigating these effects. In short-term simulations, the forces estimated by the proposed method are almost identical to the rigid-grid reference results. However, for long-term simulations, the discrepancy can become significant, dominated by phase differences in the times series. Sensitivity analysis reveals that such phase differences can occur regardless of the refill scheme, depending on the complexity of the flow characteristics.
Shinichiro Hirabayashi (Fri,) studied this question.