黏弹性流体充模过程中凝固现象的数值模拟

Simulation of solidification with phase-change in viscoelastic moldfilling process

建立了黏弹性流体在充模过程中带有相变的气一液两相模型,该模型分别由气、液两相的质量守恒方程、动量守恒方程、能量守恒方程描述,并通过引入Heaviside函数将气一液两相的方程组统一为一个方程组;建立了一个对型腔内熔体和气体都适用的修正的焓方法来描述充模过程中的相变,采用基于同位网格的有限体积方法对模型进行求解,水平集方法捕捉充模过程中的界面演化,模拟出了黏弹性流体在充模过程中的凝固现象,得出了充模过程中型腔内的温度、压力、第一法向应力差等随时间的变化;并讨论了型腔壁面温度、熔体温度、注射速度对充模过程中凝固现象的影响,研究结果表明:型腔壁面温度越高,凝固层越薄;熔体温度越高,凝固层越薄;注射速度越高,凝固层越薄,故提高型腔壁面温度、熔体温度、注射速度可以减少或消除型腔壁面附近的凝固层。

A gas-liquid two-phase model for the simulation of viscoelastic fluid mold filling process with the consideration of phase change is proposed, in which the governing equations for the melt and air in the cavity, including the mass conservation, momentum conservation and energy conservation equations, are unified into one system of equations. A revised enthalpy method, which can be used for both the melt and air in the mold cavity, is proposed to describe the phase change during the mold filling. Finite volume method on non-staggered grid is used to solve the system. The level set method is used to capture the interface evolution in the mold filling process. The distributions of physical quantities such as velocity, pressure and temperature and so on are given. The “frozen skin” layers under different temperatures and velocities are discussed in detail. Numerical results show that increasing the temperatures of the melt and cavity is a better way to get rid of the“frozen skin”layer than increasing the injection velocity.