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BC for an "artificial outlet" which is inside the fluid domain in reality

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Old   December 14, 2020, 10:01
Question BC for an outlet where the pressure unknown
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Hello everyone,

I am simulating a decanter centrifuge with MRF method. In reality it is two-phase flow for solid-liquid but I am simlulation single phase (water) with pimpleFoam for now. The actual geometry has one inlet and two outlets (one for clarified liquid, one for discharged solid particles) Because I wasn't interested in the whole geometry I cutted the geometry along its length (x-Axis). So I don't have the outlet patch for particles anymore but instead I have an outlet patch which was actually inside the geometry before. In reality, through this patch my suspension should continue flowing to the actual outlet patch for particles.

I don't know which BC I should use for that outlet patch, as it is not a real outlet patch where the fluid would flow out of the domain. I made my first simulations using fixedPressure for p and giving a small random fixedValue for U (1e-5 0 0). You can see the pressure field in attached image. (Cylindrical end is where the clarified fluid goes out and the conical end is the outlet I am asking for help) But as it is a random given value I am not sure if it is the right approach or not. I thought I could use zeroGradient for velocity but then I am not sure what I should use for pressure as I can't set the pressure to zeroGradient as well. The patch is also rotating.

For my other patches I used:

        type                flowRateInletVelocity;
        volumetricFlowRate  2.78e-5;
        value               $internalField;
         type           zeroGradient;
         type           fixedValue;
         value         (1e-5 0 0);
        type               zeroGradient;
        type           fixedValue;
        value          0;
         type           zeroGradient;
Would for example totalPressure or rotatingTotalPressure an option?
I would really appreciate if you could help me as I am stuck on my master thesis now.

Best regards,
Attached Images
File Type: jpg Dekanter_gesamt1.jpg (23.8 KB, 9 views)
File Type: jpg Dekanter_gesamt2.jpg (22.8 KB, 6 views)
File Type: jpg Schnitt.jpg (33.7 KB, 7 views)

Last edited by decanter; December 16, 2020 at 04:04.
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boundary conditons, mrf, totalpressure bc

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