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y+ calculation (for no wall function walls) (and its BC) |
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March 4, 2011, 04:59 |
y+ calculation (for no wall function walls) (and its BC)
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#1 |
Senior Member
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Dear experts,
When i use wall function i can see y+ by yPlusRAS and yPlusLES command. it calculate min, max and mean of y+ and write it on terminal. But when y+<5 i don't need wall function and i set wall as zerograDient. but by above commands no y+ would be written on terminal: Code:
Time = 0.47 Calculating wall distance Writing wall distance to field y Reading field U Reading/calculating face flux field phi Selecting incompressible transport model Newtonian Selecting RAS turbulence model LRR LRRCoeffs { Cmu 0.09; Clrr1 1.8; Clrr2 0.6; C1 1.44; C2 1.92; Cs 0.25; Ceps 0.15; sigmaEps 1.3; couplingFactor 0; } no nutWallFunction patches Writing yPlus to field yPlus End Code:
lowerWall { type calculated; value uniform 0; it may because it is zeroGradient nut, K, epsilon, R so what BC should be used when no need to wall function. U is set value 0 not zeroGradien. Regards |
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March 4, 2011, 06:27 |
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#2 |
Senior Member
Steven van Haren
Join Date: Aug 2010
Location: The Netherlands
Posts: 149
Rep Power: 15 |
Use wallGradU and formula 7.24 from pope:
tau_wall = rho*nu*(dU/dy)_wall However, this will only work if first y+ is really small, say around 1. You can use this is an wall-resolved LES or DNS. |
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March 4, 2011, 06:31 |
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#3 |
Senior Member
Steven van Haren
Join Date: Aug 2010
Location: The Netherlands
Posts: 149
Rep Power: 15 |
sorry, double post
Last edited by stevenvanharen; March 4, 2011 at 07:35. |
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March 4, 2011, 07:09 |
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#4 |
Senior Member
Steven van Haren
Join Date: Aug 2010
Location: The Netherlands
Posts: 149
Rep Power: 15 |
sorry, double post
Last edited by stevenvanharen; March 4, 2011 at 07:35. |
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March 4, 2011, 08:02 |
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#5 | |
Senior Member
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Quote:
But this formula won't give me y+. i want see y+ value by yPlusRAS or yPlusLES |
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March 4, 2011, 08:12 |
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#6 |
Senior Member
Steven van Haren
Join Date: Aug 2010
Location: The Netherlands
Posts: 149
Rep Power: 15 |
yPlusLES works fine for me.
Why does it not work for you? |
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March 7, 2011, 04:39 |
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#8 | |
Senior Member
Vesselin Krastev
Join Date: Jan 2010
Location: University of Tor Vergata, Rome
Posts: 368
Rep Power: 20 |
Quote:
y+=(y/nu)*sqrt(tau_wall/rho) Youll'have simply to know the height y of your first near wall node and then you can calculate y+ wherever you want, by sampling wallGradU or directly wallShearStress (both of these utilities work also without wall functions as bcs) Regards V. |
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March 7, 2011, 07:18 |
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#10 |
Senior Member
Vesselin Krastev
Join Date: Jan 2010
Location: University of Tor Vergata, Rome
Posts: 368
Rep Power: 20 |
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