Study On Solid-liquid Slip Boundary Of The Lattice Boltzmann Method

Boundary slippage in flow refers to the relative velocity between fluid and solid walls near the wall surface.With the advancement of interface processing technology,the weak boundary slip phenomenon has been greatly strengthened.Friction drag reduction effect caused by the boundary slip phenomenon has attracted widespread attention.In fact,simulation of this phenomenon is a challenging new topic,especially in the relatively“young”numerical method of the lattice Boltzmann method(LBM).The LBM is a numerical method based on particle collision theory which has been rapidly developed in the past three decades.Benefiting from its simple procedures,natural parallelism and the ability to handle complex boundary,this method has been widely used for the study of fluid flow,especially for the cross-scale coupling problem.However,there are several deficiencies to take this method to simulate boundary slip phenomenon.The first deficiency is how to link the microscopic boundary slip phenomenon with the macroscopic flow state.The second deficiency is that the slip boundary for liquid flow in LBM is not accurate now.These deficiencies prevent the application of the LBM method to the prediction of drag reduction performance of boundary slip materials.Therefore,this paper associates the physical slip length with the the boundary slip condition for the LBM to construct accurate slip boundary formats,which are applied to explore the influence of the boundary slip phenomenon on the macroscopic flow state of the incompressible fluid.The main contents of this paper are as follows:1.The boundary slip length is predicted by the macroscopic properties of the material.With the superhydrophobic adhesion force equation,a slip boundary condition was proposed.This method combines the existing LBM slip condition format with the liquidsolid interaction force.The slip length expression is obtained by numerical fitting.With the parameters of the material,such as contact angle,advancing angle,and receding angle,it is possible to predict the slip length of the material under macroscopic flow conditions.Through the two-dimensional plate shear flow simulation,the influence of the contact angle,sliding angle,and shear rate on the slip length is explored.The corresponding drag reduction material is manufactured by laser etching processing technology.2.In order to overcome the limited application range of the above method,we theoretically derive a solid-liquid slip boundary condition with a wider range of application and higher accuracy.Combining the existing combined slip boundary condition format and the linear slip model,new accommodation coefficient expressions are derived.These expressions,which do not depend on a specific flow model,have more extensive applicability.Further,the accuracy of the proposed schemes are verified by plate shear flow and Poiseuille flow.It has been applied to water-copper nanoparticle mixed flow and Womersley flow to explore its applicability in micro flow and unsteady flow.3.Combining the above solid-liquid slip boundary format with the WeierstrassMandelbrot(WM)fractal method,we study the coupling effects of the rough wall surface and the slip boundary on the flow of the pipeline.In this paper,a modified method is proposed for the calculation error of the coupled LBM and WM method.The accuracy of the fractal dimension of the numerical wall is also analyzed under different grid resolutions.We study the effect of rough structure forms and fractal dimensions on the flow of pipes.Based on this,we also study the application of the boundary slip phenomenon in rough pipelines.4.With the above slip boundary condition format,we study the flow around a bluff body with slip walls at low Reynolds number to explores the drag reduction effect in practical applications.In this paper,we firstly study the resistance and flow field of a square cylinder with slip boundary on both sides.Furthermore,flow around a oblique cylinder with slip walls is used to explore the influence of boundary slip phenomenon on the macroscopic flow field.In addition,we focus on the disturbance phenomenon and drag reduction effect of the side-by-side square cylinder flow with the slip boundary.Through the above studies,we analyze the effects of fluid separation and flow field changes on the drag reduction effect of boundary slip phenomenon.5.In order to generalize the boundary slip to the complex curve wall,we propose a slip boundary format for curve wall based on velocity interpolation.With the linear slip model,the slip length is transformed to be the slip velocity on the boundary.Then the boundary slip phenomenon can be simulated by the velocity boundary condition format.This format overcomes the limitation that the combined slip boundary can only be applied to a straight boundary.It also overcomes the limitation that the former slip boundary for curve wall can be applied for flow with small slip length.Therefore it has a wider applicability.Micro cylindrical Couette flow and irregular pipe flow are applied to verify the accuracy of the method.Based on this,we study the effects of boundary slip on the lift,drag and lift-drag ratio of the hydrofoil.We also analyze the change law of the lift and the drag coefficients as the slip boundary is applied at different positions of the hydrofoil.