Liquid-gas density ratio is a key property for a numerical multiphase method to model a real fluid system. Here, a chemical-potential-based multiphase lattice Boltzmann method is constructed to realize extremely large density ratios in simulations. Three technologies are developed to enhance the computational accuracy of the method. Firstly, the mesh space is decoupled from the momentum space to stretch the steep liquid-gas transition region into a gentle curve, and then the relatively denser lattice provides more accurate data for the derivative calculation. Secondly, the high-order difference promotes the gradients of density and chemical potential to obtain very high precisions. Thirdly, the inter-particle force is incorporated into the lattice Boltzmann equation using the exact difference forcing term.The simulation computations show that the model can work at very low temperatures, at which the liquid-gas density ratios reach more than 10 13 , while the model satisfies thermodynamics and Galilean invariance.

The secondary flow driven by the primary vortex in a cylinder, generating the so called “tea leaf paradox”, is fundamental for understanding many natural phenomena, industrial applications and scientific researches. In this work, the effect of wettability on the primary vortex and secondary flow is investigated by the three-dimensional multiphase lattice Boltzmann method based on a chemical potential. We find that the surface wettability strongly affects the shape of the primary vortex. With the increase of the contact angle of the cylinder, the sectional plane of the primary vortex gradually changes from a steep valley into a saddle with two raised parts. Because the surface friction is reduced correspondingly, the core of the secondary vortex moves to the centerline of the cylinder and the vortex intensity also increases. The stirring force has stronger effects to enhance the secondary flow and push the vortex up than the surface wettability. Interestingly, a small secondary vortex is discovered near the three-phase contact line when the surface has a moderate wettability, owing to the interaction between the secondary flow and the curved gas/liquid interface.