Increasing mesh resolution yields big difference in pressure?

Wizze · September 24, 2014, 06:58

Hey everyone

I am quite new to CFD and to OpenFOAM so please bear with me if this is a stupid question.

I have been looking at the cavity tutorial and when I increase the mesh resolution there is a pressure increases in the top left of the cavity and decreases at the top right. The increase and decrease of the pressure will continue as the mesh resolution gets better. I can basically obtain any pressure by changing the mesh resolution. I use the pressure legend in Paraview to determine the upper and lower pressure values.

How can this be right? Shouldn't OpenFOAM/Paraview try to depict the actual pressures regardless what the resolution is?

tomf · September 26, 2014, 07:53

Hi Wizze,

This is due to the fact that there is a singularity right at those corners. On one side there is a moving lid on the other side a stagnant wall. No-slip conditions on those sides make that there is no actual solution for the pressure in the corner. When refining the mesh this will cause the behavior you see. So it is actually the correct behavior.

Regards,
Tom

Wizze · September 26, 2014, 08:15

Thank you very much Tom :-)

September 24, 2014, 06:58	Increasing mesh resolution yields big difference in pressure?	#1
Wizze New Member Join Date: Sep 2014 Posts: 12 Rep Power: 11	Hey everyone I am quite new to CFD and to OpenFOAM so please bear with me if this is a stupid question. I have been looking at the cavity tutorial and when I increase the mesh resolution there is a pressure increases in the top left of the cavity and decreases at the top right. The increase and decrease of the pressure will continue as the mesh resolution gets better. I can basically obtain any pressure by changing the mesh resolution. I use the pressure legend in Paraview to determine the upper and lower pressure values. How can this be right? Shouldn't OpenFOAM/Paraview try to depict the actual pressures regardless what the resolution is?

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September 26, 2014, 07:53		#2
tomf Senior Member Tom Fahner Join Date: Mar 2009 Location: Breda, Netherlands Posts: 634 Rep Power: 32	Hi Wizze, This is due to the fact that there is a singularity right at those corners. On one side there is a moving lid on the other side a stagnant wall. No-slip conditions on those sides make that there is no actual solution for the pressure in the corner. When refining the mesh this will cause the behavior you see. So it is actually the correct behavior. Regards, Tom

September 26, 2014, 08:15		#3
Wizze New Member Join Date: Sep 2014 Posts: 12 Rep Power: 11	Thank you very much Tom :-)