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

What does pseudo randomness mean in turbulence

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

Reply
 
LinkBack Thread Tools Display Modes
Old   August 6, 2011, 02:27
Default What does pseudo randomness mean in turbulence
  #1
Senior Member
 
Nick
Join Date: Nov 2010
Posts: 120
Rep Power: 6
Nick R is on a distinguished road
I read in a CFD book that the randomness in turbulence is pseudo. I don't understand the meaning of the following statement
" The reason for pseudo-randomness is that small perturbations that are constantly added to the solution are enhanced exponentially in time"

-From CFD essentials by Zikanov

Can someone please explain what that statement means
Nick R is offline   Reply With Quote

Old   August 6, 2011, 05:48
Default
  #2
New Member
 
Stephen Lucchesi
Join Date: Jul 2011
Posts: 8
Rep Power: 6
insane_alien is on a distinguished road
pseudo random means it has all the appearences of being random but if you start from the exact same initial conditions and put it through the exact same process then it will be the exactly the same, ie. it is deterministic.

however, if there is even a slight difference then trial n+1 will differ from trial n by an amount proportional to the length of time the simulation has been running for.

a better way of describing turbulence would be that it is deterministic but highly chaotic.

without a way to accurately measure the position and velocity of all the molecules involved and a similarly accurate way to model their behaviour then the simulation will diverge from reality, the averages can turn out the same but down at the small details there can be big differences.

CFD is and probably always will be an approximation, it can be a pretty darn good approximation however so it is still incredibly useful.
insane_alien is offline   Reply With Quote

Old   August 9, 2011, 03:09
Default
  #3
Senior Member
 
Nick
Join Date: Nov 2010
Posts: 120
Rep Power: 6
Nick R is on a distinguished road
I see. Thanks for clarifying it.
Nick R is offline   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
Question on Turbulence Intensity Eric FLUENT 1 March 7, 2012 05:30
Turbulence length scale and integral length scale rizhang CFX 1 September 10, 2009 06:38
Discussion: Reason of Turbulence!! Wen Long Main CFD Forum 3 May 15, 2009 09:52
Code release: Flow Transition and Turbulence Chaoqun Liu Main CFD Forum 0 September 26, 2008 17:15


All times are GMT -4. The time now is 22:36.