Material Model for the filling stage of an injection mould in ANSYS Fluent

[andradesilva]

Hello,

I am using ANSYS Fluent 2020 r1 to simulate the filling stage of an injection mould. However, I don't know which material model is more suitable/correct for the flow of the molten polymer. In Fluent I can see the following options:

-Laminar
-K-Epsilon
-k-Omega
-Transition SST

From the turbulence models, the main ones are:

-RNG - Model
-Standard - Model
-Reynolds Stress Model
-Detached Eddy Simulation Model
-SST - DES Model
-Large Eddy Simulation Model


I wonder which one of these models could originate more realistic results. I appreciate any opinions regarding this matter. I thank you in advance.

Best regards,
Silva

 

[rickfischer51]

First, your flow will be extremely laminar. Small flow velocity times small characteristic dimension divided by a large viscosity results in a single digit Reynolds number. Second, polymers are non-Newtonian. They exhibit shear thinning, which means that the higher the shear rate, the lower the viscosity. Your material model will need to account for this. Mold filling simulation packages typically use Cross-WLF for a viscosity model, and a bi linear PVT curve for density and shrinkage. I think the better codes also have crystallization based PVT curves. Also, you may find it more practical to chose your material model based on available data. A complex highly sophisticated constitutive model is useless without accurate data to base it on, and I think you may find some of that data hard to come by.

Rick Fischer
Principal Engineer
Argonne National Laboratory