Application Research Of Chemical Potential Lattice Boltzmann Method

Multiphase flow is closely related to our lives,and has a wide range of applications in energy development,life sciences,production and life.Research on multiphase flow can not only help humans understand natural phenomena,master their laws of movement,but also create economic benefits,which has important scientific significance and engineering application value.The lattice Boltzmann method(LBM)based on the mesoscopic level developed in recent years has become an effective tool to simulate multiphase flow systems,and has attracted more and more attention.The application of secondary flow is very extensive,and it can be used in food processing,biotechnology and other daily life.At the same time,it plays an important role in mixing?reactor modeling and other industries.Therefore,the study of secondary flow has profound practical significance.In this paper,multiphase flow LBM method based on a chemical potential is used to establish the D3Q19 lattice model to simulate the flow phenomenon of rotating fluid with free interface,focusing on the effects of surface wettability and stirring force on primary flow and secondary vortex.By setting different surface wettability,the flow of fluid in the cylinder is simulated.It was found that when the contact angle continued to increase,the sectional plane of the primary vortex gradually changes from a steep valley into a saddle with two raised parts.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.It is noteworthy that 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.This has never been reported in previous studies.Understanding and controlling the motion of liquid drops in contact with a heterogeneous substrate have great significance in many areas,such as cooling,microfluidics,self-cleaning,and water collection.The depinning behavior of a drop on an inclined heterogeneous surface is investigated by the multiphase lattice Boltzmann method driven by the chemical potential.By controlling the contact surface between drop and substrate,we set the drop in three initial states: the moderate state,the contracted state and the elongated state;the simulation results show that different initial states of the drop lead to different depinning behavior.When the drop is initially in the moderate state,the front and rear contact angles linearly change as the slope angle continues to increase,and depinning almost simultaneously occurs at the front and rear contact lines;unilateral depinning occurs at the front contact line for the contracted state and at the rear contact line for the elongated state,with sudden oscillations of the contact angle.After that,the drop will naturally return to a similar critical sliding state.The dynamic equilibrium reflects the competition between gravity and the capillary force in the whole drop.It is clearly observed that the unilateral depinning process consists of a slow-moving stick process and a rapid slip process.By simulating strips of different widths,it is found that there is a linear positive correlation between the strip width and the rolling time of the drop,which was consistent with the previous experimental results.At the microscopic scale,based on measurement of the real-time contact angle,it is found that the local force balance in the contact line region is maintained by the unbalanced Young's force and liquid–solid friction in the stick stage,while the unbalanced Young's force provides the driving force for the motion of the contact line in the slip stage.In summary,the effects of wettability on secondary flow in three-dimensional rotating fluid and the depinning behavior of drop on chemically heterogeneous surface is investigated in this article.This improves the understanding of secondary flow and the motion of contact line,and also confirms the effective of the chemical potential model in the study of multiphase flow.