CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > OpenFOAM Post-Processing

wallGradU and wallShearStress, inconsistent result for RAS model

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   August 19, 2014, 11:08
Question wallGradU and wallShearStress, inconsistent result for RAS model
  #1
New Member
 
Lu ZHOU
Join Date: Jul 2014
Location: Lyon, France
Posts: 8
Rep Power: 3
lzhou is on a distinguished road
Hi,

I am doing a simple simulation of water flowing on a plate with RAS k-epsilon model.
My goal is to verify the simulation results with different roughness height on the surface of the plate and to calculate the wall shear stress of each case.

However, the utility wallGradU gives (36.5451 -8.58721e-05 0.000132998) for one point on the bottom wall and the utility wallShearStress gives (-0.000808236 3.08435e-09 -2.97856e-09) at this point. As I am doing a simulation of water so the dynamic (shear) viscosity is 8.9e-4 Pas. And the wall shear stress can be calculated by the equation:



So I think at this point ,the wall shear stress should be 8.9e-4*36.5451=0.0325 pa.

I would like to ask why there is the difference between the results of wallGradU and wallShearStress ? If possible, could anyone tell me the equations used in OpenFoam to calculate the wall shear stress ? Thanks !
lzhou is offline   Reply With Quote

Old   August 19, 2014, 11:22
Default
  #2
New Member
 
Lu ZHOU
Join Date: Jul 2014
Location: Lyon, France
Posts: 8
Rep Power: 3
lzhou is on a distinguished road
To add some details. The results I got is for a smooth plate with nukRoughWallFunction and Ks=0 Cs=0.5 as the boundary condition at the bottom wall. And I did not find a place to add the density of the fluid into the simulation so I guess the wall shear stress is calculated with the kinematic viscosity rather than the dynamic viscosity. Or it assumes that the density is 1 kg/m^3. I am a starter of CFD and OpenFoam so can someone help me please. Thanks !
lzhou is offline   Reply With Quote

Reply

Tags
ras compressible, wallgradu, wallshearstress

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
wallShearStress, wallGradU are inconsistent dancfd OpenFOAM Post-Processing 3 December 6, 2014 06:30
calculate and sample wallGradU & wallShearStress every output time ArathoN OpenFOAM Post-Processing 4 November 17, 2013 14:18
wallGradU or wallShearStress on Time-Averaged Velocity Field minger OpenFOAM Post-Processing 5 September 13, 2013 17:47
wallShearStress VS wallGradU bigrock OpenFOAM Post-Processing 0 July 2, 2013 05:54
k-omega-SST model (OF 1.6) - turbulent flat plate cboss OpenFOAM Running, Solving & CFD 23 November 13, 2011 02:28


All times are GMT -4. The time now is 18:14.