how to understant the Solidification Drag Model in flow3d
 

As claimed in the user manual of flow3d, a darcy-type drag force is loaded to the mushy and solidified region. When Fs = 1, the Fd will be effectively infinite. In many literatures, there will be a small constant in the denominator to aviod division by zero.

Can anyone help to explain the "effectively infinite" and how flow3d deal with the "infinite"?

Fd= TSDRG*Fs^2/(1-Fs)^3;

Hello Svenein.

As far as I understand this equation is used only if local solid fraction is between coherent point and critical point which are used defined values.

below the coherent point Fd is assumed zero. critical solid fraction is 0.67 as default and TSDRG is 1. So Fd is like 12.5. If Fd is above this value, flow stops.

So I think if drag is above the critical Fd value, solver assumes that the flow stops (or drag is effectively infinite) and switches to a different model.