Multiphase Flow Boundary Processing Method

With the development of computer technology,the computer graphics has been more and more widely used in many fields.Fluid is common in daily life,the fluid simulation is an important branch of the computer graphics,and the multi-phase flow simulation is a more complex research topic in the fluid simulation.The solid-wall boundary,gas-liquid interface and interface of different phase liquid can be regarded as the generalized boundary of multi-phase fluid,how to deal with these generalized boundaries efficiently and accurately is an important research topic in multi-phase flow simulation.This thesis first introduces the history and the research status at home and abroad of liquid-liquid boundary,gas-liquid boundary and solid-wall boundary treatment of multi-phase flow simulation,and then carries out the following three aspects to solve the above problems.In view of the problem that the density discontinuity of particles near the interface of multi-phase liquid flow leads to numerical oscillation,the density of fluid particles is modified by improving the formula of density calculation,which makes the density of the interface particles smooth transition,and the interface is stable and clear.In addition,by extracting the stranded particles and adding artificial force,we solve the problem that the out-phase stranded particles appear inside the flow and then affect the layering effect of different phase liquid.Searching for the adjacent particles of each particle is the most time-consuming step when use the SPH method to simulate multiphase flow motion.When simulating gas-liquid multi-phase flow,gas-liquid interaction will produce a large number of interfacial particles.This thesis first proposed the concept of "particles interacting with interface",using "particles interacting with interface" to speed up the search for adjacent particles of interface particles,which solves the problem that too many interactive particles of multi-phase flow simulation slow down adjacent particles search,reduces the simulation time and improves the simulation efficiency.There are two common methods to deal with gas-liquid boundary,virtual particle method and air-particle method.Compared with the virtual particle method,the air-particle method has more advantages in simulating multi-phase flow.It does not need to dynamically generate virtual particles for the gas-liquid boundary of each phase flow,which reduces the calculation amount and makes it easier to keep the gas-liquidboundary of the multi-phase flow stable.According to the problem of boundary truncation error of fluid particles at the gas-liquid boundary of multi-phase flow,this thesis improves the traditional air-particle method and puts forward a new pressure formula,which is applied to the above-mentioned "particles interacting with interface" to make the gas-liquid interface more smooth,clear without penetration phenomenon.For solving the problem of low efficiency and poor real-time performance of the traditional boundary force method when dealing with multi-phase flow solid wall boundary,we improves the traditional boundary force method and puts forward a new boundary force function,which makes the simulation speed greatly faster and the stability better.And with the increase of the number of particles in the scene,compared with the traditional boundary force method,the advantages of high simulation efficiency of this method are more obvious.The simulation results of multi-phase flow simulation with different particle numbers also verify the effectiveness of this method.