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

How to calculate shear stress?

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

Reply
 
LinkBack Thread Tools Display Modes
Old   July 7, 2014, 16:00
Default How to calculate shear stress?
  #1
AGP
Member
 
Anonymous
Join Date: Apr 2013
Posts: 34
Rep Power: 6
AGP is on a distinguished road
I am trying to calculate the shear stress on the fluid on a user defined surface in the interior of the fluid. How can I do this? What is the formula to define a custom field function for this?

Thanks,
AGP
AGP is offline   Reply With Quote

Old   July 9, 2014, 03:06
Default
  #2
New Member
 
AFM
Join Date: Nov 2013
Posts: 14
Rep Power: 5
Entwistle is on a distinguished road
Hi;

the shear stress, by its own definition, only can be computed on solid walls.

Regards.
Entwistle is offline   Reply With Quote

Old   July 9, 2014, 12:35
Default
  #3
AGP
Member
 
Anonymous
Join Date: Apr 2013
Posts: 34
Rep Power: 6
AGP is on a distinguished road
This user-defined surface is a wall. I am using a conformal mesh due to which all interfaces/walls are changed to interior regions in FLUENT.
AGP is offline   Reply With Quote

Old   July 10, 2014, 02:28
Default
  #4
Senior Member
 
Sangwoo Kim
Join Date: Jul 2014
Location: Seoul, South Korea
Posts: 104
Rep Power: 5
swtbkim is on a distinguished road
Why don't you use Reports>Surface Integrals ?
swtbkim is offline   Reply With Quote

Old   July 10, 2014, 03:11
Default
  #5
New Member
 
AFM
Join Date: Nov 2013
Posts: 14
Rep Power: 5
Entwistle is on a distinguished road
Quote:
Originally Posted by AGP View Post
This user-defined surface is a wall. I am using a conformal mesh due to which all interfaces/walls are changed to interior regions in FLUENT.
If these walls are changed into interior type, you will not be able to obtain the wall shear stress. In that case, you need to maintain these walls as walls (you can delete the mesh interface in the proper menu), so fluent will be able to show you the wall shear stress in Contours - Wall Fluxes - Wall Shear Stress.

Regards.
Entwistle is offline   Reply With Quote

Old   July 10, 2014, 16:34
Default
  #6
AGP
Member
 
Anonymous
Join Date: Apr 2013
Posts: 34
Rep Power: 6
AGP is on a distinguished road
But if I maintain them as walls, there will be no flow through them. This particular wall is the boundary between the fluid and a porous zone and I need to find the shear stresses on it. Can I write a custom field function to calculated the WSS for it?
AGP is offline   Reply With Quote

Old   July 10, 2014, 22:05
Default
  #7
Senior Member
 
Sangwoo Kim
Join Date: Jul 2014
Location: Seoul, South Korea
Posts: 104
Rep Power: 5
swtbkim is on a distinguished road
I didn't try it, but how about this?
Make plane there by using sweep surface or Surface>Plane
and calculate wall shear stress about this plane
swtbkim is offline   Reply With Quote

Old   July 11, 2014, 03:32
Default
  #8
New Member
 
AFM
Join Date: Nov 2013
Posts: 14
Rep Power: 5
Entwistle is on a distinguished road
The problem is that the wall shear stress only can be computed on walls. One possible solution is to write an UDF that applies the definition of the wall shear stress, even if your surface is not a wall: You will need the velocity derivatives and the area vector of your surface. From the definition of the viscous stress tensor you can build it and compute the force vector on your surface and its magnitude. It would be something like that:


You can implement it on a DEFINE_AT_END if your problem is transient, or in a DEFINE_ON_DEMAND if it is stationary. You will also need use the Lookup_Thread in order to specify the ID of your surface and one UDM position.

Regards.
Entwistle is offline   Reply With Quote

Old   July 11, 2014, 09:29
Default
  #9
AGP
Member
 
Anonymous
Join Date: Apr 2013
Posts: 34
Rep Power: 6
AGP is on a distinguished road
I tried doing this in CFD post. I created a new expression to calculate the shear stresses. But when I compared the contours on a real wall - the results were qualitatively the same. But the numbers were way off. I am not sure how to proceed now.
AGP is offline   Reply With Quote

Old   June 5, 2017, 03:51
Default
  #10
wxn
New Member
 
sofina
Join Date: Jun 2017
Posts: 9
Rep Power: 2
wxn is on a distinguished road
I also want to know how to calculate the shear stress on interior surface of the fluid. Did you find the solution ?
wxn is offline   Reply With Quote

Reply

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
calculate y+ and u+ -how to get wall shear stress? Ralf Schmidt Main CFD Forum 17 August 3, 2016 06:54
Calculate velocity components from shear stress Arnoldinho OpenFOAM Running, Solving & CFD 0 August 29, 2011 12:07
Fluid wall shear stress Sinead Kelly (Kelly) OpenFOAM Running, Solving & CFD 2 March 30, 2011 06:41
shear stress scalar definitions? Novak Elliott CFX 0 April 6, 2003 01:45
What is the detail definition of wall shear stress zjm FLUENT 0 January 2, 2002 08:43


All times are GMT -4. The time now is 23:50.