Study On MPI-Based Parallel Technology Of Gas-Liquid Two-Phase Flow During Mold Filling Process

The casting filling process is a key part in foundry and has an important impact on the quality of castings.A prominent problem in the numerical simulation study of casting filling two-phase flow is the slow calculation speed,which is mainly because the flow of liquid metal and air is both calculated so the mesh count to calculate is more.One of the primary means of solving this problem is to use the increasingly developing parallel technique to speed up the solution.In this study,the MPI-based parallel programming technique is used to parallelize the gas-liquid two-phase flow algorithm in the mold filling process,and finally achieve the purpose of improving the filling simulation speed.The main work of this paper are as follows:Firstly,a method of partitioning complex casting is proposed.A improved standard deviation is used as the criterion for judging how evenly the casting mesh area is divided.It is found that the dynamic programming method has better complexity in time than the enumeration method and the backtracking method.Based on the MPI parallel technology,a parallel partition model of the casting process was established.The complex casting partition method is used to evenly distribute the casting mesh information to the calculation sub-process.Secondly,the mathematical model and discrete method of SOLA-Level Set algorithm for a typical gas-liquid two-phase flow in mold filling process are studied.Combined with the characteristics of complex casting mesh distribution,the communication strategy of parallel program is designed.A mapping array method is proposed to reduce the communication overhead between sub-domains.The communication steps between subdomains are designed for the complex finite difference solution of fluid flow process.The parallel partition model is applied to the SOLA-Level Set algorithm.Finally,the parallel algorithm of this paper is applied to the numerical simulation of gas-liquid two-phase flow in the filling process of castings such as rings,plates and boxes.Through numerical comparison with the calculation results of the serial program,the numerical reliability of the parallel algorithm is shown,and a simplified version of the numerical accuracy verification method is proposed.The advantages of the complex mold partitioning method proposed in this paper are proved by comparison with the method of area division by uniform partitioning by coordinates.The results show that the parallel algorithm has a good acceleration effect,and the maximum speedup ratio is 4.6 for 8 processing cores.For the same casting,the speedup increases as the number of casting grids increases.Compared with the ring and box castings,the algorithm works best on the plate castings,and the parallel efficiency of the plate castings is about 0.6 in 1.76 million grids.The gas-liquid two-phase parallel algorithm proposed in this paper is of great significance to the development of numerical simulation technology for casting flow field.