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

Numerical Diffusion in SIMPLER.

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

Reply
 
LinkBack Thread Tools Display Modes
Old   September 24, 2000, 15:01
Default Numerical Diffusion in SIMPLER.
  #1
Ammar Hakim
Guest
 
Posts: n/a
Hi,

I am working on a problem of analysing convection in vertical co-axial cylinders. The innner cylinder is not completely "immersed" in the outer one. The outer cylinder has a prescribed iso-thermal wall temprature, and the two cylinders are exchanging engergy via radiation and convection.

I used a SIMPLER code to solve the flow field. I also have an experimental setup for this config. The exp. conf shows some convection cells that the numerical code does not predict. Also, the agreement between the tempratures is not very good, specially at the top of the innner cylinder.

I read that SIMPLER has inherent numerical diffusion that may wipe out convection cells. How do I overcome this problem? Can I try to change the differencing scheme?

Thanks in advance, Regards, Ammar.
  Reply With Quote

Old   September 24, 2000, 18:07
Default Re: Numerical Diffusion in SIMPLER.
  #2
John C. Chien
Guest
 
Posts: n/a
(1). What is your mesh size and the distribution of the cells? (2). Is the flow laminar or turbulent? (3). You need to increase the total number of cells (mesh size) until the solution is mesh independent. (4).If the flow is turbulent, you need to try the low Reynolds number model. (5). The numerical solutions should be different from the test results. Don't try to match the numerical solutions with the test data, unless your numerical solution is mesh independent.
  Reply With Quote

Old   September 25, 2000, 05:36
Default Re: Numerical Diffusion in SIMPLER.
  #3
D.M. Lipinski
Guest
 
Posts: n/a
There is nothing in SIMPLER what would foorce it to have inherent numerical diffusion. If the details in your solution do not match the experiments, then either:

1. Your mesh is not fine enough (J.Chien's post).

2. Your convection differencing scheme is too diffusive. Try some higher order schemes (e.g. the second order upwind or better QUICK if you use a structured mesh).

3. There is something wrong with your model. At first, I would try to check if your model conserves mass and energy.

regards

DML
  Reply With Quote

Old   September 26, 2000, 02:52
Default Re: Numerical Diffusion in SIMPLER.
  #4
Evgueny V. Kalabin
Guest
 
Posts: n/a
Hi, Ammar Hakim

If you use the Patankar's Power Law Scheme (as it is in classical Patankar's SIMPLER) then you have to know that the Power Law cann't find small vortices (so you have to use very big grid or other scheme, for example QUICK)

Best regards,

Evgueny
  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
Moving mesh Niklas Wikstrom (Wikstrom) OpenFOAM Running, Solving & CFD 122 June 15, 2014 06:20
numerical diffusion in tetrahedral grids Lilly Main CFD Forum 8 May 31, 2011 10:08
Numerical Diffusion in CFX John S. CFX 4 August 17, 2008 19:47
Numerical diffusion. jinwon Main CFD Forum 2 June 27, 2007 11:42
Estimation of numerical diffusion varghese FLUENT 0 March 24, 2003 06:02


All times are GMT -4. The time now is 22:53.