Free surface flow and application to the filling and solidification of liquid metals into vessels of arbitrary shape

摘要

The research work presented herein addresses the problem of the mathematical modelling of the mould filling processes as encountered in the foundry industry.ududThe quality of castings, especially aerospace components, is primarily pre-determined at the stage of mould filling within the entire casting process. The entrapment of oxide films, air voids and other impurities into the cast, caused by waves and the breaking of the molten metal surface during filling must be avoided. Otherwise, substandard casting products will result which cost the foundry industry millions of pounds in lost revenue.ududA three-dimensional control-volume, free surface flow technique known as the Scalar Equation Algorithm (SEA) has been developed as an attachment to the PHOENICS and Harwell-FLOW3D CFD codes for this study. The SEA technique uses a conserved scalar variable to represent the liquid, with an adaptation of the van Leer TVD scheme to define the instantaneous position of the interface. It is similar to the approach used by the well known Volume Of Fluid (VOF) method. However, the SEA technique deals with both air and liquid explicitly, whereas the VOF method does not.ududA technique has also been developed to allow the liquid temperature to be determined from a conserved `mixture' enthalpy. The liquid temperature is subsequently used in a solidification algorithm to simulate the effect of phase change.ududThe filling model without heat transfer and solidification has been validated against experimental data in both water experiments and actual mould filling experiments. The capability of the SEA method in capturing convoluted waves and air voids has been successfully demonstrated in an example of filling part of a mould running system. It has also been compared against the predictions from the SOLution Algorithm-Volume Of Fluid (SOLA-VOF) and Marker And Cell (MAC) methods. Examples of the developed filling model coupled with heat transfer and solidification are also given.ududTo increase computational speed, the filling model has been implemented into a parallelised version of the Harwell-FLOWSD CFD code. A speed-up of up to 80% has been achieved by using a network of heterogeneous processing nodes. Each node consists of an Intel i860 vector processor and an Inmos T800 transputer.