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

porosity value in porous baffle star-ccm+

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

Reply
 
LinkBack Thread Tools Display Modes
Old   November 23, 2008, 09:41
Default porosity value in porous baffle star-ccm+
  #1
guy
Guest
 
Posts: n/a
Hi there,

Does anybody know why setting the porosity of a porous baffle affects results when no heat transfer is included. In my work, I have already considered the baffle porosity when determining the coeff.s in the pressure drop equation, so it doesn't make sense to do it again in STAR-CCM. This is why I have set porosity to 1 and carried on. Is this correct?

  Reply With Quote

Old   November 26, 2008, 17:22
Default Re: porosity value in porous baffle star-ccm+
  #2
Guy
Guest
 
Posts: n/a
It seems that the issue of having to specify a porosity as well as alpha and beta with star has cropped up in this forum with no real answer.

In my CFD models I want to get the air velocity behind two types of windbreaks, namely a porous fence (made of yorkshire boarding) and permeable screens.

The two materials have the same porosities yet have different alpha's and beta's. So I assume correctly setting their porosity coeff's in the software would be innacurate. That is unless porosity is basically a factor to "tune" CFD results, in which case I'm out of luck cos I have no experimental data on this. Am I right by letting this equal to 1 and what are the max values for the alpha/beta coeffs accepted by star-ccm+.

Hopefully someone out there has the answer

  Reply With Quote

Old   November 26, 2008, 17:30
Default Re: porosity value in porous baffle star-ccm+
  #3
Pauli
Guest
 
Posts: n/a
If I remember correctly, alpha and beta are for the pressure drop side while porosity has to do with heat transfer. It's in the manual.
  Reply With Quote

Old   November 26, 2008, 17:55
Default Re: porosity value in porous baffle star-ccm+
  #4
Guy
Guest
 
Posts: n/a
I know, i have read the manual. What it says is "The viscous shear stress is computed as a linear combination of the shear stress in the fluid and the shear stress at the wall. The porosity provides the linear weighting."

In fact the porosity specification has a huge effect on the velocity predictions.
  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
How to define the porous baffle Aga CD-adapco 0 July 24, 2007 01:58
hot porous baffle azmir CD-adapco 0 February 9, 2006 20:25
Porous baffle and porous media Jan CD-adapco 0 June 8, 2002 09:23
porosity of baffle raymond CD-adapco 4 April 4, 2002 04:03
Determining alpha and beta for porous baffle Liaqat Khan CD-adapco 1 October 27, 2000 04:44


All times are GMT -4. The time now is 04:12.