# Why is the lid driven cavity problem not symmetrical?

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 March 6, 2023, 10:16 Why is the lid driven cavity problem not symmetrical? #1 New Member   Join Date: Mar 2022 Posts: 6 Rep Power: 3 I'm currently working on the application of Dakota in OpenFOAM using a case study from wolfdynamics.com, and in this case varying the top wall velocity between -2 and +3m/s and measuring the pressure at the centre of the cavity. As the title suggests, I get results that indicate that the results are not symmetrical when taking a positive vs a negative velocity, for example the pressure using -2m/s is -0.146Pa but at +2m/s is roughly -0.053Pa. Plotted the distribution here https://imgur.com/a/E11KAXj. There must be something about the lid driven cavity or perhaps the CFD process in general that I am misunderstanding, because in my eyes the problem looks to be symmetrical. If anyone knows what's going here, I would be really interested to find out why this is the case. Thanks!

March 6, 2023, 12:38
#2
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Filippo Maria Denaro
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Quote:
 Originally Posted by canderous I'm currently working on the application of Dakota in OpenFOAM using a case study from wolfdynamics.com, and in this case varying the top wall velocity between -2 and +3m/s and measuring the pressure at the centre of the cavity. As the title suggests, I get results that indicate that the results are not symmetrical when taking a positive vs a negative velocity, for example the pressure using -2m/s is -0.146Pa but at +2m/s is roughly -0.053Pa. Plotted the distribution here https://imgur.com/a/E11KAXj. There must be something about the lid driven cavity or perhaps the CFD process in general that I am misunderstanding, because in my eyes the problem looks to be symmetrical. If anyone knows what's going here, I would be really interested to find out why this is the case. Thanks!
The solutions with +/- sign must be specular, provided the magnitude is the same.
But the solution is not symmetric in the centerline owing to the relevance of the convection. A symmetric solution can be obtained at vanisching Reynolds number.
I suggest to check what happens with a very low velocity.

March 7, 2023, 04:12
#3
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Paolo Lampitella
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Quote:
 Originally Posted by canderous I'm currently working on the application of Dakota in OpenFOAM using a case study from wolfdynamics.com, and in this case varying the top wall velocity between -2 and +3m/s and measuring the pressure at the centre of the cavity. As the title suggests, I get results that indicate that the results are not symmetrical when taking a positive vs a negative velocity, for example the pressure using -2m/s is -0.146Pa but at +2m/s is roughly -0.053Pa. Plotted the distribution here https://imgur.com/a/E11KAXj. There must be something about the lid driven cavity or perhaps the CFD process in general that I am misunderstanding, because in my eyes the problem looks to be symmetrical. If anyone knows what's going here, I would be really interested to find out why this is the case. Thanks!
The negative and positive case should, ideally, be specular (rather than symmetric), as mentioned by Filippo.

As the practical implementation relies on floating point numbers, you can't expect the exact same solution at the bit level but, obviously, there is something wrong in one of your two solutions if they have differences above the lowest precision you used among the two, which seems to be the case.

I don't know well enough OF, but every other CFD solver I used would work as you expect in this case.

PS: at a certain point you write about using different velocities in magnitude. I am obviously assuming that it is a typo and you just changed sign to the lid velocity, not its magnitude.

 Tags cavity, dakota, openfoam