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

Help! How to hold turbulence in a 2d channel flow RANS simulation

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   July 27, 2012, 11:58
Default Help! How to hold turbulence in a 2d channel flow RANS simulation
  #1
Member
 
dw
Join Date: Jul 2012
Posts: 32
Rep Power: 13
1/153 is on a distinguished road
Newbie here.

I am doing a 2D rans simulation to investigate some turbulence models. I am wondering how to make the flow turbulent?

For example in a simple Re_tau=180 channel flow, or a little bit more than that. Pressure gradient driven, using some low Re turbulence model, and keep the mesh having y+<1.

Then I set the initial nut=100*nu, k/e>100*delta_t, mass is kept constant on the solver's side (I am using an unsteady solver (URANS)).

But I found the flow is always laminar or laminarized. This is very annoying.

But I read so many papers, they all have a perfect velocity profile, How did they do that? Any secrets?

Or what did I do wrong?

Any ideas?

--------
1/153
1/153 is offline   Reply With Quote

Old   July 27, 2012, 14:44
Default
  #2
Senior Member
 
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,760
Rep Power: 71
FMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura about
Quote:
Originally Posted by 1/153 View Post
Newbie here.

I am doing a 2D rans simulation to investigate some turbulence models. I am wondering how to make the flow turbulent?

For example in a simple Re_tau=180 channel flow, or a little bit more than that. Pressure gradient driven, using some low Re turbulence model, and keep the mesh having y+<1.

Then I set the initial nut=100*nu, k/e>100*delta_t, mass is kept constant on the solver's side (I am using an unsteady solver (URANS)).

But I found the flow is always laminar or laminarized. This is very annoying.

But I read so many papers, they all have a perfect velocity profile, How did they do that? Any secrets?

Or what did I do wrong?

Any ideas?

--------
1/153
Could you post your velocity profile compared to the DNS at Re=180?
FMDenaro is offline   Reply With Quote

Old   July 27, 2012, 14:49
Default
  #3
Senior Member
 
lakeat's Avatar
 
Daniel WEI (老魏)
Join Date: Mar 2009
Location: Beijing, China
Posts: 689
Blog Entries: 9
Rep Power: 21
lakeat is on a distinguished road
Send a message via Skype™ to lakeat
<deleted><deleted><deleted><deleted>
__________________
~
Daniel WEI
-------------
Boeing Research & Technology - China
Beijing, China
Email
lakeat is offline   Reply With Quote

Old   July 27, 2012, 14:57
Default
  #4
Member
 
dw
Join Date: Jul 2012
Posts: 32
Rep Power: 13
1/153 is on a distinguished road
Thanks for helping. Yes the velocity profile is here: [shared just for 24 hours]

http://f.imgtmp.com/Dcdfq.jpg
1/153 is offline   Reply With Quote

Old   July 27, 2012, 15:59
Default
  #5
Member
 
dw
Join Date: Jul 2012
Posts: 32
Rep Power: 13
1/153 is on a distinguished road
Is that because 2D cant sustain the turbulence structures, so to damp out all the turbulence? Or is that I should use RANS not URANS?
1/153 is offline   Reply With Quote

Old   July 27, 2012, 16:09
Default
  #6
Senior Member
 
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,760
Rep Power: 71
FMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura about
Quote:
Originally Posted by 1/153 View Post
Is that because 2D cant sustain the turbulence structures, so to damp out all the turbulence? Or is that I should use RANS not URANS?

No ... you are solving a 2D statistically steady solution, you never see in RANS any other variable that zero-order statistics....
But your problem is that you are solving a smaller Re number, your profile arrives at y+ about 10 at the half-heigh!
FMDenaro is offline   Reply With Quote

Old   July 27, 2012, 16:16
Default
  #7
Member
 
dw
Join Date: Jul 2012
Posts: 32
Rep Power: 13
1/153 is on a distinguished road
I will test with other LRN models to see if my new implemented model is wrong somewhere. But have you ever use steady RANS to get a correct profile before? Which turb model did you use? Thanks

Last edited by 1/153; July 27, 2012 at 16:32.
1/153 is offline   Reply With Quote

Old   July 27, 2012, 16:39
Default
  #8
Senior Member
 
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,760
Rep Power: 71
FMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura about
RANS is perfect in turbulent channel flow, you have some wrong in your setting/input
FMDenaro is offline   Reply With Quote

Reply

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
Open Channel Flow ElanMorin FLUENT 4 February 25, 2015 17:26
Heated vertical channel flow RANS ep4 OpenFOAM Running, Solving & CFD 0 November 24, 2008 10:37
Code release: Flow Transition and Turbulence Chaoqun Liu Main CFD Forum 0 September 26, 2008 18:15
LES turbulence decaying in channel flow cfdIsMad CFX 4 July 4, 2008 07:29
compressible channel flow.. R.D.Prabhu Main CFD Forum 0 July 17, 1998 18:23


All times are GMT -4. The time now is 05:31.