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

Why SIMPLE family algorithms are not used in LES?

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

Reply
 
LinkBack Thread Tools Display Modes
Old   November 18, 2002, 09:24
Default Why SIMPLE family algorithms are not used in LES?
  #1
Linfeng BI
Guest
 
Posts: n/a
Hi, everyone: Such algorithms as SIMPLE and PISO also has the ability to solve unsteady problems. But why they are not widely used in DNS/LES? Is it only because of their large computational expense?

thanks, Linfeng
  Reply With Quote

Old   November 18, 2002, 21:31
Default Re: Why SIMPLE family algorithms are not used in L
  #2
Ulises
Guest
 
Posts: n/a
Because they have dissipative character at small scales close to the smallest scales resolved and therefore modify the spectrum of those scales. A scheme is called dissipative when it amplifies or reduces some modes amplitudes. A centered scheme is purely dispersive, does not modify the amplitude of any scale but only its phase. As soon as you use a not purely centered scheme in a purely regular mesh, one introduces small numerical dissipation that can artificially stabilize or unstabilize the computation.

In DNS and specially LES one has to be able to solve accurately the amplitude of the modes up to the smallest scales
  Reply With Quote

Old   November 18, 2002, 23:07
Default Re: Why SIMPLE family algorithms are not used in L
  #3
versi
Guest
 
Posts: n/a
I guess SIMPLE type algorithms can do DNS and LES on staggered grids where seemly pure central differences can be used for any spatial derivatives. But it seems there is few such work. I do not know why.
  Reply With Quote

Old   November 18, 2002, 23:18
Default Re: Why SIMPLE family algorithms are not used in L
  #4
Ulises
Guest
 
Posts: n/a
Oh yeah you're right...sorry I had a terrible memory lapsus...

Yes I think SIMPLE algorithm would require too many sub-steps for each time step for unsteady calculations. It is best suited for steady calculations (or calculations in which you seek converged steady solution) and DNS-LES are inherently unsteady...or something like that, hope my memory is not failing again
  Reply With Quote

Old   November 19, 2002, 11:35
Default Re: Why SIMPLE family algorithms are not used in L
  #5
Linfeng BI
Guest
 
Posts: n/a
Then it should be the case of computational expense? By the way, I am not sure whether central difference is more difficult to converge than upwind.
  Reply With Quote

Old   November 19, 2002, 20:05
Default Re: Why SIMPLE family algorithms are not used in L
  #6
FUFU
Guest
 
Posts: n/a
Sometimes time accuracy is more important than any other parameters. In DNS/LES more than second order time differencing scheme is recommended. And in spacial differencing, upwind families schmes are too dissipative so that cannot resolve small scale chacteres.
  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
Normaly how long does it take for a simple LES to converge? Basy OpenFOAM 1 October 16, 2011 03:51
LES basic and simple questions. dshawul Main CFD Forum 0 October 4, 2010 10:56
SIMPLE family and Fractional Step Method Geon-Hong Main CFD Forum 2 April 5, 2010 18:05
SIMPLE FAMILY ALGORITHEM behzad Main CFD Forum 2 July 4, 2005 03:13
about SIMPLE algorithms anne Main CFD Forum 7 March 7, 2003 04:39


All times are GMT -4. The time now is 23:59.