什么是mushy zone constant？——fluent的糊狀系數(shù)

2016-10-06 by:CAE仿真在線來(lái)源:互聯(lián)網(wǎng)

在使用fluent的融化凝固模型的時(shí)候,必須輸入一個(gè)mushy參數(shù),如下圖所示

在根據(jù)翻譯為糊狀系數(shù),默認(rèn)值為1e5,那什么叫糊狀系數(shù)呢?

下面是ansys原始文檔,根據(jù)該文檔有幾點(diǎn)需要說(shuō)說(shuō):

1、該值一般不需要特別輸入,保持默認(rèn)值大多數(shù)情況都可以,一般范圍為1e4——1e7之間

2、mushy zone constant是一個(gè)系數(shù),該系數(shù)是用于動(dòng)量公式里面,如公式18-6所示

3、該值越大材料凝固的速度越小,特別大的值可能會(huì)導(dǎo)致求解收斂困難。

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The pull velocity is included to account for the movement of the solidified material as it is continuously withdrawn from the domain in continuous casting processes.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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