Calculation of dimensionless wall distance

Felix_Sp · November 2, 2021, 08:28

Hello everyone,

I was wondering how one can calculate the dimensionless wall distance

or

in Reef3D. As far as I know one can calculate it with the following formula:

$y^* = \frac{y_p*\sqrt{C_\mu^\frac{1}{2}*k_p}}{\nu}$

with $C_\mu = 0.09$ ,

the TKE in point p,

wall-distance of point p and $\nu =$ kinematic viscosity (taken and modified from here: https://www.afs.enea.it/project/nept.../th/node99.htm).
To do that in Reef3D I would use P 29 to get the wall distance. Then I would calculate the given formula in ParaView (e.g. with the Calculator-filter) and apply a Threshold- or Clip-filter for the wall-distance with the given uniform cell-size.

My first question is whether my thinking is correct and whether that way I am actually getting the value of

for the nodes closest to the wall in the mesh (i.e. where the wall functions are applied).
My second question is whether this is the only way so far to actually get the dimensionless wall distance or whether I have overlooked something in the manual.

Thanks for your help in advance!

valgrinda · November 13, 2021, 10:04

Hi Felix,

P 29 1 is mostly for debugging, I don't think it is suitable for calculating y+. Here, I would recommend just calculating it manually based on your selected dx. Then I would use the velocity based equation for y+, not the TKE based one.

Felix_Sp · November 15, 2021, 13:50

Hey thanks for the answer. I'll try that!

November 2, 2021, 08:28	Calculation of dimensionless wall distance	#1
Felix_Sp Member Felix S. Join Date: Feb 2021 Location: Germany, Braunschweig Posts: 85 Rep Power: 6	Hello everyone, I was wondering how one can calculate the dimensionless wall distance or in Reef3D. As far as I know one can calculate it with the following formula: $y^* = \frac{y_p\sqrt{C_\mu^\frac{1}{2}k_p}}{\nu}$ with $C_\mu = 0.09$ , the TKE in point p, wall-distance of point p and $\nu =$ kinematic viscosity (taken and modified from here: https://www.afs.enea.it/project/nept.../th/node99.htm). To do that in Reef3D I would use P 29 to get the wall distance. Then I would calculate the given formula in ParaView (e.g. with the Calculator-filter) and apply a Threshold- or Clip-filter for the wall-distance with the given uniform cell-size. My first question is whether my thinking is correct and whether that way I am actually getting the value of for the nodes closest to the wall in the mesh (i.e. where the wall functions are applied). My second question is whether this is the only way so far to actually get the dimensionless wall distance or whether I have overlooked something in the manual. Thanks for your help in advance!

November 13, 2021, 10:04		#2
valgrinda Super Moderator Hans Bihs Join Date: Jun 2009 Location: Trondheim, Norway Posts: 377 Rep Power: 17	Hi Felix, P 29 1 is mostly for debugging, I don't think it is suitable for calculating y+. Here, I would recommend just calculating it manually based on your selected dx. Then I would use the velocity based equation for y+, not the TKE based one. __________________ Hans Bihs Team REEF3D www.reef3d.com

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November 15, 2021, 13:50		#3
Felix_Sp Member Felix S. Join Date: Feb 2021 Location: Germany, Braunschweig Posts: 85 Rep Power: 6	Hey thanks for the answer. I'll try that!