什么是mushy zone constant？——fluent的糊状系数

2016-10-06 by:CAE仿真在线来源:互联网

在使用fluent的融化凝固模型的时候,必须输入一个mushy参数,如下图所示

在根据翻译为糊状系数,默认值为1e5,那什么叫糊状系数呢?

下面是ansys原始文档,根据该文档有几点需要说说:

1、该值一般不需要特别输入,保持默认值大多数情况都可以,一般范围为1e4——1e7之间

2、mushy zone constant是一个系数,该系数是用于动量公式里面,如公式18-6所示

3、该值越大材料凝固的速度越小,特别大的值可能会导致求解收敛困难。

18.5. Momentum Equations

The enthalpy-porosity technique treats the mushy region (partially solidified region) as a porous medium. The porosity in each cell is set equal to the liquid fraction in that cell. In fully solidified regions, the porosity is equal to zero, which extinguishes the velocities in these regions. The momentum sink due to the reduced porosity in the mushy zone takes the following form:

(18–6)

where is the liquid volume fraction, is a small number (0.001) to prevent division by zero, is the mushy zone constant, and is the solid velocity due to the pulling of solidified material out of the domain (also referred to as the pull velocity).

The mushy zone constant measures the amplitude of the damping; the higher this value, the steeper the transition of the velocity of the material to zero as it solidifies. Very large values may cause the solution to oscillate.

The pull velocity is included to account for the movement of the solidified material as it is continuously withdrawn from the domain in continuous casting processes. The presence of this term in Equation 18–6 allows newly solidified material to move at the pull velocity. If solidified material is not being pulled from the domain, . More details about the pull velocity are provided in Pull Velocity for Continuous Casting.

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