Model Research And Application Based On Chemical Potential Lattice Boltzmann Method

Multiphase flow is ubiquitous in natural phenomena and engineering applications.Studying the motion mechanism of multiphase fluids is of great significance for understanding the laws of nature,improving production processes and promoting the development of disciplines.The lattice Boltzmann method has been developed into an effective tool for simulating multiphase flow systems.Its efficiency,accuracy and robustness have also been widely proven and successfully applied to many surface wetting science and engineering related fields.Based on the chemical potential boundary conditions,the geometrical method is used to calculate the contact angle in real time.Firstly,the position of the intersection of the three-phase contact point and the nearest droplet gas-liquid interface and the horizontal grid line is determined by linear interpolation method,and then the contact angle is calculated by using an inverse trigonometric function.Based on this mesoscopic method,the change in contact angle in droplet deformation on chemically isomeric surfaces was investigated.The droplets falling above the solid surface and the droplets suspended below the solid surface were simulated by setting different chemical potentials to change the hydrophilic and hydrophobic properties of the solid surface.Under the influence of gravity,the simulated contact angle is consistent with the theoretical expectation of the spherical crown method.The contact angle can be linearly adjusted by the surface chemical potential,and it is verified that the droplet mass is independent of the contact angle.Under the action of gravity,although the droplets of different sizes have obvious deformations of different degrees,the contact angle calculated by the simulation remains unchanged,and the theoretical analysis that the microscopic contact angle is independent of gravity is verified.The chemical potential multiphase flow model was used to study the motion of the droplets on chemically heterogeneous inclined surfaces and the contact angle hysteresis.When the chemical potential of the hydrophilic-hydrophobic strip on the surface of the substrate is constant,the contact angle and contact length of the steady-state droplets on different strip widths are symmetric.And the quasi-static contact angle hysteresis on the strips of different widths is identical.When the droplets are destabilized and roll occurs,a periodic stick-slip motion is exhibited and a dynamic contact angle hysteresis is thereby produced.The effects of heterogeneous surfaces with different chemical potentials and different strip widths on the periodic motion of the droplets were simulated.Since the droplets take more time across the long strip,the period of motion of the droplets gradually increases as the strip width increases.In the case where the strip width is the same,the larger the difference in the contact angle,the more hydrophilic the heterogeneous surface is,and the longer the period of motion of the droplet.These simulation results further confirm that the chemical potential multiphase flow model and the mesoscopic contact angle measurement method are effective.Based on the chemical potential multiphase flow model,a proportional coefficient relaxation is performed on the moment space in the lattice Boltzmann method and the feature quantity in the computational grid space,and the high order difference is introduced to accurately calculate the derivative and gradient of the feature quantity.We propose a chemical potential multiphase flow model with superlarge density ratio.The two-phase coexistence density of different equations of state is simulated and compared with the theoretical results of Maxwell's iso-area structure,which proves that the model satisfies the thermodynamic consistency at very low temperatures.The numerical simulation results are in good agreement with the theoretical values,and the liquid phase and gas phase of each equation of state reach an ultra-high density ratio:VDW exceeds 10¹⁰,PR exceeds 10¹¹,and RKS and CS exceed 10¹³.The surface tension of different equations of state is calculated by simulation,and the verification model satisfies Laplace's law.By simulating the surface tension and interface width of the different proportional coefficients of the state equation at the same temperature,it is proved that the transition between the moment space and the computational grid is stable and accurate.The simulation of the simple droplet splatter phenomenon,and this phenomenon verified that the model satisfies the Galilean invariance.