Numerical Investigation On Gas-liquid-solid Coupling Dynamics Using The Lattice Boltzmann Method

The research on gas-liquid-solid coupling dynamics is a multiphase flow problem,including fluid-solid interface,gas-liquid interface and their interaction,is an important subject in the field of water-conservancy machinery,hydraulic machinery and the ship-ocean engineering,related to the protection and optimization design of the equipments directly.The phenomenon of flow around a body will happen when fluids flow through underwater structures.Water load fluctuation on the structure will cause vibration,and even structural damage.Especially,in the field of military equipment,even the slight vibration of structures will seriously affect the deep stealth performance of underwater vehicles(such as a submarine),and endanger the safety of navigation and personnel.Under the influence of underwater complex environment,the interaction between device and fluid is a very complicated process,which is often accompanied by the presence of bubbles,such as cavitation bubbles near a propeller and bubbles in a pipe or valve flow.Therefore,the research on gas-liquid-solid coupling dynamics can not only be academic significance,but also can provide some technical supports for practical engineering application.The key issue in gas-liquid-solid coupling dynamics is the coupling problem,including the fluid-solid interface,gas-liquid interface and their interaction.Though the process of occurrence,movement,break and fusion of bubbles appears in the macroscopic level,it is based on the microscopic properties.The main research on this problem is implemented by experiments,which is limited by experiment condition,observation skill and high price.Theoretical research is another way,but restricted to its complex resolving,massly assumption and general solution.Different from the former methods,numerical simulation is the third way,which is high-speedly developed with the development of modern high-performance computers and numerical methods.In this work,from the perspective of underwater moving interfaces,the lattice Boltzmann method(LBM)based on the theory of molecular dynamics is used to calculate the multiphase coupling problem including fluid-solid interface,gas-liquid interface and their interaction.Lattice Boltzmann method is often regarded as a kind of meshfree particle algorithm in the mesoscopic level between the macroscopic level and the microscopic level.The density distribution function is utilized to determine the distribution of particles in the fluid field.Through the multi-scale expansion,the relationship between the lattice Boltzmann equation and the macroscopic control equation,such as the Navier-Stokes equation can be established.Different from the traditional numerical methods including the finite difference method,the finite element method and the finite volume method,the lattice Boltzmann method has the advantages that the traditional methods can not compare,such as a clear physical background,the natural parallelism and the flexible parameter controllability.Taking the advantage of the lattice Boltzmann method in the field of computational fluid dynamics,it is applied in the study of gas-liquid-solid coupling dynamics.Based on the developed numerical models,the research on fluid-solid interface,gas-liquid interface and their interaction is carried out.The main research contents and results are as follows:(1)A novel lattice Boltzmann method is developed to handle static fluid-solid interfaces.Here,a virtual boundary is established between the actual physical boundary and the adjacent fluid node according to the half-way bounce-back scheme.The variables on the virtual boundary are obtained using the finite difference method,and the offset of a actual boundary relative to the grid line is considered.Besides,the method can be extended to the treatment of simple moving fluid-solid boundaries.Based on some classical numerical examples,including Poiseuille flow,Couette flow,flow around a stationary circular cylinder and rotating Couette flow,the developed method is verified.(2)A novel lattice Boltzmann method is developed to handle moving fluid-solid interfaces.In this method,the immersed-boundary method is introduced.Complex moving interfaces in the flow field can be described based on the Eulerian-Lagrangian coordinate system.An implicit speed correction algorithm is adopted to ensure the non-penetration and non-slip boundary condition at the fluid-solid interface.At the same time,the numerical stability of the method is improved using the multiple relaxation coefficient matrix instead of a single relaxation coefficient.Therefore,a novel method based on the implicit velocity correction for multiple-relaxation immersed-boundary lattice Boltzmann method is developed.Some classical numerical examples are carried out to verify the method and the coupling characteristics between the flow and the rotating plate are study.(3)A parallel multiphase scheme of lattice Boltzmann method is developed to handle gas-liquid interfaces.The scheme is based on the principle of the free-energy multiphase principle.Two groups of the lattice Boltzmann equation are used to describe the two-phase flow system,in which one is used to solve the Navier-Stokes equation including the influence of viscosity and surface tension,and the other is used to solve the Cahn-Hilliard equation.The numerical stability of the method is improved by using step-by-step operation.The OpenMP multi-core shared memory technology is used to construct a three dimensional parallel model.The reliability of the method is verified by the Laplace law and the bubble deformation.Based on this,the single bubble and bubble-bubble interaction dynamics are studied.(4)The characteristics of bubble motion in a narrow region,including the inner bubble in a pipe and the bubble in a wall driven shear flow,are studied.For the case of a inner bubble in the pipe,the numerical stability and expansibility of the proposed interface processing method in dealing with the static fluid-solid interface and the gas-liquid interface in a gas-liquid-solid system is verified.Meanwhile,the effects of blocking ratio and eccentric ratio on bubble topological distortion and trajectory are researched.For the case of a bubble in the wall driven shear flow,the reliability of the proposed method dealing with the moving fluid-solid interface and the gas-liquid interface in the gas-liquid-solid system is verified.The influence of Capillary number,Reynolds number and the moving wall is researched.(5)The coupling characteristics between the bubble and the flat,curved solid boundary in an open field are studied.By modifying the size ratio,the fluid flow attribute and the interaction process between the bubble and the two type of boundaries are observed.Meanwhile,the lattice Boltzmann method with the multiple relaxation scheme which can improve the numerical stability and the fluid viscosity limit,is used to build up the one-and two-dimensional models for acoustic waves.Based on this,the propagation of acoustic waves generated by the underwater bubble pulsation or other disturbances is studied.