Flow rate and phi not matching??
 

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????

Hello Brett,


What solver are you using?
First thing coming to my mind would be volume flowrate VS mass flowrate.

Hi Yann,

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

Any other thoughts?

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.

@Bdew8556 I'm having the exact same issue but the ratio of volumeFlowRate and phi is coming out as 30 in my case.

Have you managed to solve this issue?