Learning Forum

[sfaron]

Hi everyone !

I am trying to simulate the solidification of a binary alloy with the multiphase - Volume-Of-Fluid model (primary phase being my alloy, secondary phase is argon inert gas). I am using Ansys fluent 2021 R1, Double precision and in parallel on an HPC.

At first, I was using the Lever rule (no species transport), I only had two fluids materials (the argon, and my alloy, with its liquidus and solidus temperature) for solidification.

However, I now want to change my solidification path following Scheil rule. I've enabled the species transport equations (witout reactions, and no Options ticked), created my mixture made of two species - which compose the binary alloy - and set the thermophysical properties of the mixture (volume-weighted-mixing-law for density, piecewise-linear Specifict heat and thermal conductivity, constant viscosit, constant-dilute-appx for the Mass diffusivity, the order of magnitude being 10e-09).

My solute has also a piecewise linear density, constant molecular weight, the standard state enthalpy (at Tref = 300 K) to the order of magnitude 1e+08, coming from the Fluetn database of the pure solid element representend by this species), and the alloy-related slope of liquidus, partition coefficient, eutectic mass fraction and the same diffusion in solid as the mass diffusivity of the mixture. The solvant has a different molecular weight, but same density, standard state enthalpy and reference temperature, the other options are empty as not requiered (automatically set to zero).

A UDF set the initial volume of fluid of the mixture during initialization (basically, if any cell of my Eulerian mesh are below a given value, C_VOF(c, pt[0]) = 1.0; and C_VOF(c, pt[1]) = 1.0 - C_VOF(c, pt[0]);).

A heat source is then applied from the UDF with Discrete Phases. When I was using the Lever rule, the material was melting and then solidifying well. However, now, the material seems to react as if it was a gas, although its temperature is below the Eutectic temperature (hence, below pure element melting temperature and solidus temperature).

I don't know if I've done something wrong, perhaps something had to be changed in the UDF by going from one fluid to using the mixture ? I doubt it, as C_VOF(c, pt[0]) referes to the phase and not the material itself.

Feel free to ask any question if I've not been clear, unfortunately I am not allowed to give many in-depth details about the simulation and elements used ...

[Karthik Remella]

Hello Can you simplify the model and see if it behaves alright? If that works, my suggestion would be to add complexity one by one at a time. Perhaps, it is a simple issue with the model set-up in Fluent.
Karthik

[sfaron]

Hello Kremella, sorry for the late reply due to the Easter break. Thanks for your reply !
I just tried with constant values for my species and my mixture, but the issue is still the same. How would you suggest to simplify the model ?

Thanks in advance,
Sebastien

[sfaron]

Hi again I found the issue, which came from the UDF. I've added an extra force in the momentum source term, which was responsible of the wrong metal behaviour...
It is fixed now