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Gravity Casting: Pressure Outlet vs. Stagnation Inlet

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Old   May 28, 2014, 16:05
Default Gravity Casting: Pressure Outlet vs. Stagnation Inlet
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Hello CFD Community!

I just started a co-op where I am continuing work done by another student.
We're modeling a simple gravity casting simulation and comparing the simulated cooling curve to those measured on an actual casting of identical geometry to our model. This is in hopes that eventually we will be able to predict grain growth for any model before we cast it.

The inlet of the sprue is modeled as a pressure inlet. The vents are modeled as stagnation inlets as opposed to pressure outlets. This was done in an attempt to restrict the flow (say in the event of a splash) when the melt reaches the top of the mould, but given our geometry and the fact that as this is a gravity casting, I cannot imagine the melt splashing at all.

I have a sneaking suspicion that the stagnation inlet is causing some issues with the solver and, therefore, is throwing off the accuracy of our simulation. Everywhere I have read, it is suggested that mass flow inlets should be paired with pressure outlets; this especially makes sense when you consider that the mould is filled with air before the melt is poured, thus we do actually have a fluid moving through the pressure outlet during the simulation.

I am curious as to you're take on this. Any advice is welcome .

Cheers,

Joe
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Old   May 28, 2014, 17:17
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I would use the pressure outlet since you shouldn't use the compressible condition for an incompressible fluid
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Old   May 29, 2014, 09:28
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Thanks for the quick reply, me3840.

Julian, CD-Adapco's casting expert, recently suggested I introduce a slight compressibility on the melt EOS to enhance convergence and robustness.

Would it then be appropriate to model the outlets as stagnation inlets?
Or is it still a best practice to stick with a pressure outlet for the solver's sake?
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boundary conditions, casting, pressure conditions, stagnation pressure

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