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K-omega SST at values of y+ greater than 1

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Old   July 4, 2019, 22:38
Question K-omega SST at values of y+ greater than 1
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Sebastian Pelletier
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Hello all,


I have a rather unique situation that I am not sure exactly how to handle. I am using the kw-SST model to resolve the heat transfer coefficients on an impingement surface at which the y+ is < 1. For this I need the k-w SST model as its one of the best for the impingement case. However my model also has inlet pipes that I don't care about wall fluxes and am simply developing a velocity profile. I would resolve these inlets to a y+ of 1 although the geometry is very prohibitive causing inflation to be not exactly an option and the number of cells needed to be very high.

My question is essentially If I leave the y+ at the inlet pipes greater than 1 in the 30-100 range. Is the kw sst model defaulting to wall functions or will it attempt to resolve and give garbage results? Should I just remove the inlet pipes and develop a separate velocity profile?
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Old   July 5, 2019, 09:21
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Paolo Lampitella
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It depends from the specific implementation. A wf is just a bc, it has nothing to do, formally, with the kw sst model.

Actually, the model is known to be among the few being able to go down to low y+ values.

Thus, the implementer of the kw sst model in the specific code you are using, might have actually decided to not implement wf at all.

Once you find out what is the specific implementation in the code you are using you will actually find out what is happening at your inlet.
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Old   July 5, 2019, 09:27
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If you are using Fluent, let me suggest you to either go to that forum or please give people reading you here sufficient contest and interest to answer you here on an otherwise software specific issue.

The fluent implementation of all kw models uses an y+ insensitive wf treatment, which means that your wf will be active wherever y+ is above 3-5
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Old   July 7, 2019, 20:04
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Thank you very much for your time and replies, I was unaware that the wf implementation would be program and not model specific, my apologies. As I am using Fluent you essentially answered my question thank you again
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k-w sst, wall functions, y plus selection

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