# Y+ and convergence

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 February 14, 2017, 08:04 Y+ and convergence #1 New Member   Prem Sagar Join Date: Dec 2016 Posts: 7 Rep Power: 7 Hey! Im trying to solve for a compressible flow boundary layer phenomena. The Y+ average reaches from ~30 to 2 in 2000 iterations exponentially. But then it's taking forever to go to one. It's decreasing for sure but in the order of 0.0001 per iteration. The boundary layer is not resolved. How can I make it reach below 1 faster enough to resolve the boundary layer? Any suggestions would be appreciated

 February 14, 2017, 14:42 #2 Senior Member   Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 4,783 Rep Power: 56 The y+ is a property of your grid and flow solution. Sitting around waiting does not make it go down. Either change your grid or change your flow. It starts at some value because of your initial condition. It changes with each iteration because your solver is iterating the solution field, updating the solution with each iteration. If your solution has converged, then your y+ will be a fixed value. To resolve the boundary layer you need to make sure there are enough grid points in that region of your flow field, not wait for the solver to "solve for the boundary layer".

 February 14, 2017, 22:01 #3 New Member   Prem Sagar Join Date: Dec 2016 Posts: 7 Rep Power: 7 I agree. I used this online calculator for the first grid spacing. https://geolab.larc.nasa.gov/APPS/YPlus/ But it never seems to go below 1 even with 10 times smaller grid spacing I got from this calculator. :/ I was under the impression probably it's the solver taking more iterations to resolve each grid layer close to to wall. Correct me if I'm wrong. Thank you

 February 15, 2017, 00:42 #5 New Member   Prem Sagar Join Date: Dec 2016 Posts: 7 Rep Power: 7 Thank you! I was only concerned because I used the area average of y+ as the monitor. With the average at about 2, there were regions where the y+ was about 5-6. I guess I'll see my boundary layer profile and call the shots.

 Tags boundary layer, yplus

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