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

whats the difference between laminar simulation and DNS

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   March 25, 2015, 09:58
Default whats the difference between laminar simulation and DNS
  #1
New Member
 
Join Date: Nov 2014
Posts: 2
Rep Power: 0
zrjtju is on a distinguished road
hi everybody
I am wondering whats the difference between laminar simulation and DNS. what i cannt understand is that when we simulate laminar flow, certainly there is no turbulent model used. does that mean that we solve the NS equation directly? or some special methods are used to prevent small perturbation to grow?
I am simulate laminar flow using code developed by some individual. my problem is that if I dont use any turbulent model, the flow field eventual become messy. the residual would grow up as well. so can somebody please tell me the difference between them and recommend me some papers or books
all the best
zrjtju is offline   Reply With Quote

Old   March 25, 2015, 10:33
Default
  #2
Senior Member
 
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,101
Rep Power: 66
FMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura about
Quote:
Originally Posted by zrjtju View Post
hi everybody
I am wondering whats the difference between laminar simulation and DNS. what i cannt understand is that when we simulate laminar flow, certainly there is no turbulent model used. does that mean that we solve the NS equation directly? or some special methods are used to prevent small perturbation to grow?
I am simulate laminar flow using code developed by some individual. my problem is that if I dont use any turbulent model, the flow field eventual become messy. the residual would grow up as well. so can somebody please tell me the difference between them and recommend me some papers or books
all the best

DNS is a simulation performed by solving NS equation without any turbulence model. It requires to use grids fine to get the smallest structures of the flow. An CFD code can formally run in DNS mode.
Laminar flow is only a particular regime of the flow, which is, of course, solved in DNS mode.
In your case if you have laminar flow and see residual growing, that sounds more a numerical instability
FMDenaro is offline   Reply With Quote

Old   March 25, 2015, 23:02
Default
  #3
New Member
 
Join Date: Nov 2014
Posts: 2
Rep Power: 0
zrjtju is on a distinguished road
hi
thanks,very much. that's very helpful. Can i understand it this way, as long as my numerical schemes are stable, whether it's laminar or DNS depends on my grid? of course the boundary condition and the accuracy of my schemes are taken into account.
zrjtju is offline   Reply With Quote

Old   March 26, 2015, 03:38
Default
  #4
Senior Member
 
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,101
Rep Power: 66
FMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura about
however, laminar flows are always solved in DNS formulation ...
FMDenaro is offline   Reply With Quote

Old   March 29, 2015, 15:10
Default
  #5
Senior Member
 
Simbelmynė's Avatar
 
Join Date: May 2012
Posts: 523
Rep Power: 14
Simbelmynė is on a distinguished road
1. Laminar flow with large grid spacing will probably give you a solution that is laminar, even if there is a possibility for turbulence.

2. I think it is important to make a distinction between a laminar solution and a laminar solver.

3. A DNS resolves all temporal and spatial scales of turbulence. Given that the flow is known to be laminar then a laminar solver can be said to be DNS since you do not need to resolve any turbulence at all.
Simbelmynė is offline   Reply With Quote

Reply

Tags
dns, laminar model

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Does laminar mean DNS? kkpal OpenFOAM Running, Solving & CFD 1 April 21, 2013 17:11
help me for a DNS simulation dima13 OpenFOAM 11 June 15, 2012 23:21
Laminar solver? LES? or DNS? Ray Main CFD Forum 5 March 19, 2003 10:19
Laminar model the same as DNS? Kerrin Main CFD Forum 6 February 24, 2003 15:12
DNS simulation sources. Arturo Ortiz FLUENT 0 February 1, 2001 13:15


All times are GMT -4. The time now is 19:05.