Numerical Simulation Of Mold Filling Of Castings Based On The BFC System

Mold filling is one of key processes to insure good quality of castings. The study of numerical simulation of mold filling has the significant importance for predicting and controlling casting defects. In order to improve the simulation precision and calculation efficiency for modeling the mold filling process of complicated and curved-shape castings, the body-fitted coordinate (BFC) method is applied in the numerical simulation of mold filling process. The main finished research work is as follows.In order to compare with BFC method, firstly, a two-dimensional numerical simulation for fluid flow based on the orthogonal coordinate system has been carried out. According to the principal of inertia and continuity of fluid flow, an improved VOF method is proposed to calculate the fluid flow and free surface. The SIMPLE-VOF method and SOLA-VOF method based on the orthogonal coordinate system are analyzed and compared. A two-dimensional numerical simulation program for mold filling process with SIMPLE-VOF method based on staggered grid has been developed. The simulated results agree well with the results published in the literature.The methods of BFC grid generation are analyzed and studied. The governing equations for elliptic partial differential equation system are deduced in detail. The generated BFC grids using Thomas-Middlecoff method are compared with those using directly solving Laplace equation method. The results show that the generated BFC grids with Thomas-Middlecoff method are better than those using directly solving Laplace equation method.The incompressible Navier-Stokes equation in the BFC system is deduced. The comparison between staggered grid method and non-staggered grid method has been made based on the BFC system. It is noted that under BFC system non-staggered grid method is more effective than staggered grid method. All variables are stored at the same set of nodes. The Cartesian velocity component has been used as the variables of the difference approximation equations. In order to decrease the pressure oscillations, the pressure-weighted interpolation method can be used to solve the interfacial inversed velocities.The momentum equation expressed with stress is applied for free surface, which make the surface satisfy with the momentum conservation. An improved VOF method based on the orthogonal coordinate system is applied to BFC system, which is used to calculate the moving free surface with time.Comparison of the SIMPLE-VOF method and the SOLA-VOF method which are both based on the BFC system has been made. The result shows that the SIMPLE-VOF method works in the BFC system, whereas SOLA-VOF method is not suitable to the BFC system.The SIMPLE-VOF algorithm based on the BFC system is proposed, based on which a two-dimensional numerical simulation program with BFC-SIMPLE-VOF method has been developed. The developed program is applied to simulate the mold filling in curved-shape mold cavities, and the results are compared with the SIMPLE-VOF method based on the orthogonal coordinate system. It can be noted that in the complicated and curved regions the simulated continuity of fluid flow by BFC-SIMPLE-VOF method is better than that simulated by the SIMPLE-VOF method based on the orthogonal coordinate system. When the similar precision is ensured, a large of memory size and CPU time can be saved by using BFC method.