CFD Online Logo CFD Online URL
Home > Forums > Main CFD Forum

relaxation factor

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

LinkBack Thread Tools Display Modes
Old   February 1, 2008, 15:27
Default relaxation factor
Posts: n/a
What are relaxation factors and how do they affect our flow field?

  Reply With Quote

Old   February 3, 2008, 09:14
Default Re: relaxation factor
Posts: n/a
Dear Adam,

Relaxation schemes are iterative procedures that are employed to solve system of algebraic equations. This appears in CFD when you make use of implicit schemes for time stepping . The update looks like U^(n+1) = U^n + alpha*delU, where U is the variable being updated. The term alpha is the relaxation factor. When alpha<1, we refer to it as underrelaxation, mostly used to prevent the solution procedure from diverging and when alpha>1 we refer to it as overrelaxation, often used to accelerate convergence. The use of these factors affect the convergence of the iterative procedure, and to that extent the solution update and hence the solution.

Hope this helps


  Reply With Quote

Old   February 3, 2008, 09:45
Default Re: relaxation factor
Posts: n/a
Hi Ganesh

Thank you so much for your answer. What i have understood from your answer is that if we tamper with relaxation factor we are not letting the flow field take its natural course. As a result it affects the out come of our results. Then why do we even have to have such a tool because if we tamper with this factor we are bound to get wrong results right?

Regards Adam
  Reply With Quote

Old   February 4, 2008, 11:10
Default Re: relaxation factor
Posts: n/a
At steady state (or convergence of an inner iteration for time-accurate results) the effect of under-relaxation disappears since at convergence u^n = u^n+1. Thus under-relaxation does not lead to wrong results as long as it is applied correctly.
  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
Under relaxation factor for external coupling dhxlxz CFX 10 August 11, 2015 20:52
under relaxation factor and the steady state jing113cn FLUENT 0 November 2, 2009 13:13
Relaxation factor Benzaa Main CFD Forum 1 August 18, 2009 07:27
Question on adjusting relaxation factor CFD Rookie Main CFD Forum 3 January 26, 2004 15:37
Relaxation factor Moon CD-adapco 1 June 13, 2003 11:13

All times are GMT -4. The time now is 09:04.