CFD Online Logo CFD Online URL
Home > Forums > CFX

Calculating average wall shear?

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

LinkBack Thread Tools Display Modes
Old   March 8, 2007, 07:12
Default Calculating average wall shear?
Posts: n/a
I need to calculate the time averaged wall shear stress for a transient flow application. Wall shear stress magnitude is not available in the Transient Statistics tab.

What I normally do in this situation is to write the value of a CEL expression (which calculates the variable I'm interested in) into an algebraic additional variable e.g.

algebraic additional variable: avMyVar, [units], unspecified domain additional variables: avMyVar: algebraic equation, set value to expMyVar define CEL expression: expMyVar = ((Wall Shear x Component)^2+(Wall Shear y Component)^2+(Wall Shear z Component)^2)^0.5

Once this is done, avMyVar appears in the Transient Statistics tab and the appropriate average can be selected.

While this approach works fine when using volumetric variables in expMyVar, it generates an error in CFX solver for wall shear magnitude:

+--------------------------------------------------------------------+ | ERROR #001100279 has occurred in subroutine ErrAction. | | Message: | | A transient statistic has been requested but could not be initial- | | ised. A likely reason for this is that the specified variable on- | | ly exists on boundaries. The following statistic will not be gene- | | rated - TRNAVG: avMyVar | | | | | +--------------------------------------------------------------------+

Clearly it doesnt like the fact that wall shear magnitude is a non-volumetric quantity. Does anyone know how to get around this problem?
  Reply With Quote

Old   March 12, 2007, 17:12
Default Re: Calculating average wall shear?
Posts: n/a
I *think* you can do this in version 11.0. No need to create the AV and CEL expression, Wall Shear should just be there in the list of variables on the Trn Stats tab in Pre. There's also a new Trnavg CEL operator, e.g you can refer to variable.Trnavg in CEL expressions.
  Reply With Quote

Old   March 12, 2007, 18:55
Default Re: Calculating average wall shear?
Posts: n/a
I see.

I'm still on 10 and was planning to write a fortran routine to access wall shear tomorrow.

If anyone could confirm Stumpy's findings for CFX 11 I could just bite the bullet and do the upgrade now.
  Reply With Quote

Old   March 17, 2007, 10:42
Default Re: Calculating average wall shear?
Posts: n/a
I can now confirm that wall shear is available in Transient Statistics for CFX 11.
  Reply With Quote


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
What does “Mean Wall Shear Stress” mean? dfytanid FLUENT 3 October 17, 2016 01:05
Wall Shear Stress GamFlu FLUENT 0 June 11, 2011 03:52
Problems with wall shear stress. xiexiehezuo FLUENT 1 September 22, 2009 12:26
What is the detail definition of wall shear stress zjm FLUENT 0 January 2, 2002 08:43
what the result is negatif pressure at inlet chong chee nan FLUENT 0 December 29, 2001 06:13

All times are GMT -4. The time now is 22:34.