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

Upwind vs High Resolution

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

Reply
 
LinkBack Thread Tools Display Modes
Old   April 17, 2004, 04:50
Default Upwind vs High Resolution
  #1
Liwau
Guest
 
Posts: n/a
Dear All,

I can get a very good converged solution for a gas-solid two-phase flow by using upwind scheme. However, when I change the upwind to high resolution, no converged results come out. Could anybody please tell me how to solve this problem? Thanks.

Liwau
  Reply With Quote

Old   April 18, 2004, 16:07
Default Re: Upwind vs High Resolution
  #2
BAK_FLOW
Guest
 
Posts: n/a
Hi Liwau,

there is always a trade-off between accuracy and robustness. The upwind scheme is very robust because it adds significant numerical diffusion and increases the diagonal dominance of the equation system. Second order schemes produce more accurate results on reasonable grids but have dispersive errors which can result in over-shoots and under-shoots in the solution (commonly called solution wiggles) and difficult to converge solutions. For more on this there is a great deal written, some good sources are the texts by Ferziger and Peric, Versteeg, etc See the books online section of this site for more info.

The hi-resolution scheme is a blend of second order and first order which tries to maintain as much second order as possible. This is a desirable mix however, because the order of the scheme is a function of the solution this also adds an additional level of non-linearity.

There are a number of things you can try:

1. refine the mesh in the regions of hight gradients

2. use a fixed blend factor as high as you can say 0.9 or higher

3. smaller time steps

Good Luck,

Bak_Flow
  Reply With Quote

Old   April 20, 2004, 11:49
Default Re: Upwind vs High Resolution
  #3
Jane
Guest
 
Posts: n/a
Hi guys,

What second order scheme does CFX use? Central differencing? Power Law? QUICK?

Thanks, Jane
  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
High Resolution (CFX) vs 2nd Order Upwind (Fluent) gravis ANSYS 3 March 24, 2011 03:43
about upwind and high resolution Eric CFX 1 December 30, 2006 07:56
high resolution or upwind erick CFX 2 March 9, 2006 01:09
upwind vs high resolution Richard CFX 3 February 20, 2006 07:35
Multicomponent fluid Andrea CFX 2 October 11, 2004 05:12


All times are GMT -4. The time now is 04:53.