In continuous casting processes, the solidified matter is usually continuously pulled out from the computational domain, as shown in Figure 24.2.1. Consequently, the solid material will have a finite velocity that needs to be accounted for in the enthalpy-porosity technique.
As mentioned in Section 24.2.2, the enthalpy-porosity approach treats the solid-liquid mushy zone as a porous medium with porosity equal to the liquid fraction. A suitable sink term is added in the momentum equation to account for the pressure drop due to the porous structure of the mushy zone. For continuous casting applications, the relative velocity between the molten liquid and the solid is used in the momentum sink term (Equation 24.2-8) rather than the absolute velocity of the liquid.
The exact computation of the pull velocity for the solid material is dependent on the Young's modulus and Poisson's ratio of the solid and the forces acting on it. FLUENT uses a Laplacian equation to approximate the pull velocities in the solid region based on the velocities at the boundaries of the solidified region:
FLUENT uses the following boundary conditions when computing the pull velocities:
The pull velocities are computed only in the solid region.
Note that FLUENT can also use a specified constant value or custom field function for the pull velocity, instead of computing it. See Section 24.3.2 for details.