| Summary: | 碩士 === 國立成功大學 === 工程科學系 === 89 === A casting process, including both filling and solidification processes, is a transient problem of thermal flow with the movement of free surface and the release of latent heat. The computer simulation of the process can simultaneously predict the flow and temperature fields, which can assist the control of casting quality.
In this paper, a mathematical model was built to simulate the filling and solidification processes of liquid metal in a mold cavity. To determine the position and profile of liquid/air interface, the Van Leer difference scheme was used to solve the conserved scalar equation. The SIMPLE method was utilized solve the flow fields of both liquid metal and air. The effective specific heat method and the temperature recovery scheme were applied to handle the release of latent heat and the latter one was used to make up for the latent heat loss of the former one.
In this paper, two-dimensional cases were used to test the proposed model. From the computing results of flow field, it can be found that the profiles of free surface are similar to those in the literature. With an improved scheme of flow-rate control, the relative error of total flow volume is less than 0.1% at every time step. When Froude number is less than one, the fluid flow is easy to break up and the downstream flow will affect the upstream one. When Froude number is bigger than one, the fluid flows upward along the mold wall and it will not affect the upstream flow.
From the computing results of temperature field, it can be found that there is a small heat-affected zone of air (similar to a thermal boundary layer) distributed along the liquid/air interface. When the mold cavity is filled up with liquid metal, the effect of fluid flow can be seen clearly from the temperature distributions and the central high-temperature zone deviates from the center point of the mold cavity. The temperature variation becomes small little by little and the solidification direction is from the outer to the inner.
|
|---|
