Coupled lattice Boltzmann–large eddy simulation model for three-dimensional multiphase flows at large density ratio and high Reynolds number

Discussion on interface deformation and liquid breakup mechanism in vapor–liquid two-phase flow

“…However, the Allen-Cahn-based LB model was pointed out to have higher numerical accuracy and stability in solving the index parameter than the Cahn-Hilliard-based LB model. [31] Following this point, the singlerelaxation-time (SRT) operator form [32] and the multiplerelaxation-time (MRT) operator form [21] for the Allen-Cahnbased LB model were developed. This MRT phase-field-based LB model is presented in the following.…”

“…where the subscripts l and v represent the liquid phase and the vapor phase. 𝑒 i , c s , and ω i are the discrete velocity, the lattice sound speed, and the weighting coefficient in D3Q15 lattice model, respectively, and s i (𝑢) can be calculated from [21] s…”

“…Different mechanisms describe the fluid movement from different perspectives, as previously mentioned, the RTI and KHI are two instability mechanisms characterizing the vapor-liquid phase interface deformation, while, the capillary instability and endpinching mechanism are difficult to recognize and easily confused with the former. Adopted in this work is a threedimensional (3D) phase-field-based LB model [21] to simulate three benchmark cases, analyze the fluid movement based on the capillary instability and the end-pinching mechanism, and clarify the stances of different mechanisms in vapor-liquid two-phase flow. The rest of this paper is organized as follows.…”

A Three-Dimensional Non-Orthogonal Multiple-Relaxationtime Phase-Field Lattice Boltzmann Model for Multiphase Flows at Large Density Ratios and High Reynolds Numbers

“…In this simulation, the density ratio of the heavy phase and [Jia et al, 2019), We s = 40, Δ = 1 and Δx = 0.7, at ρ h /ρ l = 5000 and μ h /μ l = 117.8. light phase is set as ρ h /ρ l = 1000 with a viscosity ratio μ h /μ l = 67, which corresponds to the realistic water-air system. The same case has been studied previously using the phase field LB models, but most studies used unrealistic parameters (e.g., a small Reynolds number, usually lower than 2000 and 2-D simulation (Zhang et al, 2022;Liang et al, 2018;Fakhari et al, 2017;An et al, 2021). In our simulation, we reproduce experimental cases for a water droplet impacting a thin water film, by using the D3Q27 ULBM (NMRT) PF model with the Local scheme.…”

“…Besides, the momentum-based model has better potential in simulating large viscosity ratio and density ratio as it follows the H-theorem (Zu and He, 2013). Moreover, the momentum-based model has been improved by using a weighted MRT collision operator (Fakhari et al, 2017), coupling large eddy simulations (An et al, 2021), and proposing a simplified force term (Liang et al, 2018). Nevertheless, discontinuity at the phase interface is produced in the momentum-based model, which causes velocity fluctuations and hampers its applications in simulating large-density ratio multiphase flow (Zu and He, 2013).…”