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Urgent Please: is this a flow simulation error?

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Old   August 13, 2012, 22:03
Default Urgent Please: is this a flow simulation error?
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Urgent Please: Is this a Solidworks error? velocity inlet doesn't match up with volume flow rate goal

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Hey guys...

I've been getting this error and I want to know how to get past it, it's a simple setup:

i have a hollowed pipe so a circular inlet and i've put some lids on either side:

inlet BC: 1 m/s
inlet Area: 1 m^2

you'd think this would give me a volumetric flow rate into the pipe of 1 m^3/s, but no.. see the surface goals i have below:

Goal Name UnitValue Averaged Value \
SG Volume Flow Rate outlet[m^3/s] -3.987011588 -3.987011588SG
Volume Flow Rate inlet[m^3/s] 3.987011588 3.987011588SG
Av Velocity outlet[m/s] 1.000000904 1.000000813SG
Av Velocity inlet[m/s] 1 1

Can someone please help me out? I need to validate this model by tomorrow

p.s. - This was done in SW2012 if that matters
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Old   August 17, 2012, 11:05
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Boris Marovic
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Hi Diego,
sorry for the late reply, but do you have an image of the model in a section view and the mesh at the inlet so I can see how good the mesh is?
Please use the "use CAD geometry" setting in the cut plot switched off for this screenshot. This shows you the real mesh that is used for the solver, with that option enabled it gives your nicer images, it's not wrong but not the best way to analyse the mesh quality.

I assume the mesh resolution on the surface is not accurate. If the mesh is good you should see around 1m^3 volume flow rate simply because 1m*1m^2 should not be much higher except if the represented surface is not as big as it should be.
You can check that with the surface parameters at this inlet and check for the "CAD Fluid Area" and "Surface Area". They shouldn't have a too big difference. Since you use 1m/s as BC you can already see the surface should be the the same value. The difference between these two surface values is due to the surface approximation of the mesh and should be very small if the mesh is good.

I hope this helps,
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Old   September 1, 2012, 09:44
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Joe Galliera
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The flowrates that you are calculating are too close to 4 to not ignore the fact that your geometry may be incorrectly defined. (The velocity is good, the flowrate in matches out so everything else is good.) Remember that Area equals pi*D^2/4; you might be forgetting to divide by 4. The diameter for an Area of 1 m^2 should be approx. 1.12838 m.
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