Research Of Multi-interface Coupling Character Based On The Lattice Boltzmann Method

Multiphase flow is a common phenomenon,which is widely existed in nature and industry,such as hydraulic machinery,energy exploitation,ship and ocean.It is great significance to improve production technology and promote social progress by carrying out the related mechanism research of multiphase flow.Multiphase flow is a subject,which studies mixed fluid flow contained gaseous,liquid and solid,and it usually involves two or more different phases or different components of materials with a clear interface,such as bubble's interface,free surface and their coexistence system.Therefore,the research of multi-interface coupling character is the content in the multiphase flow,and its background is engineering application.Meanwhile it is a difficult problem in the multiphase flow research.When underwater mechanical equipment interacts with fluid,it accompanied the presence of bubbles,such as the bubbles in the turbine and cavitation bubbles near a propeller.Those phenomena would cause the vibration of the structures;some go so far as to cause erosion or damage.This thesis is based on gas-liquid-solid coupling system,involves turbine,ships and propeller propulsion system,starts from the bubble with bubble,bubble with free surface and solid with a free surface coupling,and adopt the lattice Boltzmann method to analyze multiple interface coupling problems.Due to multiple interface coupling involved the large deformation and nonlinear problems,the traditional macro methods such as the finite element method has some limitations to solve those problems.However,the lattice Boltzmann method is a mesh-free method,which uses some simple rules of particles motion to substitute the complicated and variable macroscopic phenomena.It also has great advantages in interface track and parallel calculation.Therefore,the lattice Boltzmann method is a promising approach.The work is based on fluid dynamics,multiphase flow and fluid structure interaction and uses the lattice Boltzmann method to analyze single bubble floatation,bubble-bubble coupling,bubbles busting and water impacted with structure.The main research contents in the present are as follows:To studying the single bubble floatation which involved big density ratio,large deformation and stress fluctuation problem,the single-phase free surface model was adopted,which introduced the advanced format of the surface tension,to set up the single bubble floating model.On this basis,it explores the effects of relevant parameters about gas-liquid two phases coupling on the movement characteristics and flow field structure.Under different radius ratio of bubbles,fluid viscosity coefficient and surface tension coefficient,it showed when the radius of bubbles and the surface tension coefficient increase and the viscosity of the liquid decreases,the bubble velocity and the topological deformation degree would increase.Based on the single bubble floating,bubble-water model was established to explore free surface distortion and fusion in process of bubble bursting.And the free surface fusion process and flow field structure were analyzed under different fluid viscosity coefficient and found that it wound inhibitor droplet splash and liquid level fluctuation with the radius of bubbles increasing.Two-bubble coupling model was set up to explore the interface of bubble fusion,large deformation and refactoring phenomenon,influence factors were analyze in the process of gas-liquid interface coupling and discussed the effects of initial position and double bubbles radius on the process of interface coupling characteristics and the structure characteristics of the flow field.And it found that the coupling of the double bubbles flow field structure is more complicated,compared with the single bubble.Especially,when one bubble radius is larger,the bigger bubble flows more apparently.At the same time,it inhibits the movement of small bubbles.Based on gas-liquid two-phase interface coupling,the solid boundary is introduced to establish gas-liquid-solid three phases coupling model to explore the problem of the solid interface and free surface coupling.And it analyzes free surface flow and liquid pressure fluctuations in process of the cylinder into water.In view of different surface tension and viscosity,the influence of changing a parameter on the structure into the water is explored.And found that the viscosity is an important factor and cannot be ignored.The higher viscosity coefficient can effectively inhibit the phenomenon such as spatter droplet and Liquid level fluctuation...