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Flow rate and phi not matching??

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Old   May 28, 2019, 19:28
Default Flow rate and phi not matching??
  #1
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Brett
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Hi guys,

I've got an interesting situation.
I've got 2 inlet patches, each set to:

Inlet1
{
type flowRateInletVelocity;
volumetricFlowRate constant 65;

}

Now after monitoring the velocity magnitude at a few slices in the domain im happy the simulation has converged. In the U file at one of these advanced time steps, think its time step 4840. I have this:

Inlet1
{
type flowRateInletVelocity;
volumetricFlowRate constant 65;
extrapolateProfile false;
value uniform (0 6.02545 0);
}


All look ok right??

Well if I try this command:

postProcess -func 'patchAverage(name=Inlet1,U,p)' -latestTime




surfaceFieldValue patchAverage(name=Inlet1,U,p):
total faces = 865
total area = 10.7876


Time = 4840

Reading fields:
volScalarFields: p
volVectorFields: U



Executing functionObjects
surfaceFieldValue patchAverage(name=Inlet1,U,p) write:
average(Inlet1) of U = (0 6.02545 0)
average(Inlet1) of p = 101325


End



Again this is what I expect.

This is where it gets weird:

If I run

postProcess -func "flowRatePatch(name=Inlet1)" -latestTime


I get.......

surfaceFieldValue flowRatePatch(name=Inlet1):
total faces = 865
total area = 10.7876


Time = 4840

Reading fields:
surfaceScalarFields: phi



Executing functionObjects
surfaceFieldValue flowRatePatch(name=Inlet1) write:
sum(Inlet1) of phi = -30.743


End





So how can it be a surface of approx 10m2 with an average velocity of approx 6m/s giving my requested flow rate of 65m3/s (approx) but have a flux across it equal to 30.743m3/s???

Any thoughts????
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Old   May 29, 2019, 05:11
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Yann
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Hello Brett,


What solver are you using?
First thing coming to my mind would be volume flowrate VS mass flowrate.
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Old   May 29, 2019, 19:34
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Brett
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Hi Yann,

Just simpleFoam, so I've not defined the density.

Any other thoughts?
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Old   July 1, 2019, 06:02
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Tobias Holzmann
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Hi,

without knowing your case. I think you are doing anything wrong - somewhere. I just redone all your steps in the pitzDaily case and everything works fine. No problems at all an all results are as expected.

By the way, please use code-tags.
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