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

Simple Wall Boundary Conditions for Turb. Flow

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   May 24, 2002, 00:05
Default Simple Wall Boundary Conditions for Turb. Flow
  #1
Greg Perkins
Guest
 
Posts: n/a
Hi Guys,

I'm writing some code to use in a commercial software which models a wall in a manner similar to the vof method. Thus the wall can move through the domain - I won't go into the details...

Anyway, I'm most interested in the heat and mass transfer at the wall, however due to computational limiations I expect the near wall control volume to be at least several centimetres from the wall.

What I'd like to know is how best to model the heat and mass transfer to the wall.

It appears to me that the standard wall function approach still requires fine meshes near the wall for accurate results. Has anybody got any experience with using this approach but with large cell sizes near the wall?? What is the penalty in terms of accuracy etc?

Another method, used in chem eng a lot (but not cfd) is to use some sort of correlation, since the first cell could very well be in the bulk flow region. The problem with correlations is picking a good one, and that they only span a limited range of conditions.

So, I'm just wondering if anybody has come across this type of issue before. And what if any suggestions you have!

I know the ideal is to resolve the b/l at the wall etc., but this won't be possible in this particular model for various reasons, so I'm looking for another way. I don't need absolute accuracy but I would like to be able to capture the heat and mass transfers over a reasonable range of conditions....

Thanks Greg
  Reply With Quote

Old   May 27, 2002, 10:37
Default Re: Simple Wall Boundary Conditions for Turb. Flow
  #2
Jonas Larsson
Guest
 
Posts: n/a
It is difficult to give any advice without knowing what kind of flow you expect at the wall - is it an attached flow with a developed boundary layer? turbulent? impinging flow? separated flow? Or can you perhaps expect all kind of flows?

From what you say it sounds as if your best option is to use a correlation. Wall functions on a very coarse grid, perhaps even on a grid with varying grid-density, and with unknown and varying flow conditions does not sound very good to me.
  Reply With Quote

Old   May 27, 2002, 19:19
Default Re: Simple Wall Boundary Conditions for Turb. Flow
  #3
Greg Perkins
Guest
 
Posts: n/a
Thanks Jonas,

I'm currently using correlations and having had a bit of a look at the wall functions stuff recently I agree with you.

Actually I expect a range of flow conditions but mainly some sort of natural convection at the wall.

To help me understand this I've decided to do some detailed runs using a model which resolves the b/l to help justify my correlation assumptions on the coarse model.

Thanks

Greg
  Reply With Quote

Old   May 28, 2002, 11:41
Default Re: Simple Wall Boundary Conditions for Turb. Flow
  #4
Jonas Larsson
Guest
 
Posts: n/a
For natural convection you are certainly much better off using a correlation - any good heat transfer book, like Incropera & Dewitt, should have a number of correlations for horisontal or vertical walls. A search for "natural convection correlation" on google gives several nice examples. Maya Heat Transfer Technologies also has a few online calculators for natural convection - Maya's tools are linked from CFD Online in the Resources/Online Calculators/Heat Transfer section.
  Reply With Quote

Old   May 29, 2002, 00:10
Default Re: Simple Wall Boundary Conditions for Turb. Flow
  #5
Greg Perkins
Guest
 
Posts: n/a
Thanks alot Jonas

Greg
  Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
non reflective boundary conditions for incompresible flow Pascal_doran OpenFOAM Programming & Development 16 August 25, 2015 06:35
Low Speed Flow Boundary Conditions Paul Bateman FLUENT 2 January 10, 2013 14:01
Wall boundary condition (a very simple question) safa_c FLUENT 1 August 15, 2010 06:05
Boundary Conditions for Incompressible Flow Bob FLUENT 0 April 7, 2006 22:28
Multicomponent fluid Andrea CFX 2 October 11, 2004 06:12


All times are GMT -4. The time now is 22:44.