CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > CFX

Turbulant airflow behind 2D airfoil

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   January 21, 2008, 00:19
Default Turbulant airflow behind 2D airfoil
  #1
Adam
Guest
 
Posts: n/a
I have been working several months trying to teach myself CFX and working through the tutorials. I have been searching this site and I cannot find what I am doing wrong. When I walk through the tutorial for the blunt body, I see recirculation behind the body. However, I am unable to recreate this with an airfoil at different AOA and I always have a laminar flow. What am I doing wrong. I know this is a general question so please let me know what would be helpful. Sorry in advance for being crude with much of this. I am self tought and I have no one to ask.
  Reply With Quote

Old   January 21, 2008, 03:22
Default Re: Turbulant airflow behind 2D airfoil
  #2
Farid
Guest
 
Posts: n/a
Hi Adam,

Which Fluid model did you select in the domain?

  Reply With Quote

Old   January 21, 2008, 18:34
Default Re: Turbulant airflow behind 2D airfoil
  #3
Adam
Guest
 
Posts: n/a
Air Ideal Gas

Also SST Turbulence model
  Reply With Quote

Old   January 21, 2008, 23:43
Default Re: Turbulant airflow behind 2D airfoil
  #4
Farid
Guest
 
Posts: n/a
From my experience, I think the SST turbulence model doesnt capture the flow separation. Cause, I also ran different simulations for different angles of attack using SST model but didnt get any separation.

I used Gamma Theta Transition model with SST turbulence model and got good results with the prediction of flow separation. So, I suggest you do the same thing.

  Reply With Quote

Old   January 22, 2008, 17:49
Default Re: Turbulant airflow behind 2D airfoil
  #5
Glenn Horrocks
Guest
 
Posts: n/a
Hi,

The SST turbulence model can model separations, however it has certain accuracy problems in predicting the exact separation point (both in terms of chordal location and AOA for stall). You will find all RANS turbulence models have problems accurately predicting this so it is not unique to SST.

What Reynolds number are you using, and what airfoil?

Glenn Horrocks
  Reply With Quote

Old   January 23, 2008, 05:15
Default Re: Turbulant airflow behind 2D airfoil
  #6
Farid
Guest
 
Posts: n/a
Hi Glenn,

I have tried with Mach No.=0.3 and Re=0.54 Million for AOA=5,8,10 and 12 deg.The flow was fully turbulent and the model was SST.But I didnt get any separation. On the other hand, Using GAmma Theta Transition model with SST Turbulence model under the same condition, I got separation for AOA=8,10 and 12 deg.

Thanks

Farid
  Reply With Quote

Old   January 23, 2008, 05:32
Default Re: Turbulant airflow behind 2D airfoil
  #7
Farid
Guest
 
Posts: n/a
NACA 0012.
  Reply With Quote

Old   January 24, 2008, 17:55
Default Re: Turbulant airflow behind 2D airfoil
  #8
Glenn Horrocks
Guest
 
Posts: n/a
Hi,

To get accurate results you need a refined mesh, sufficiently small timesteps (if transient) and sufficient convergence. Have you check all these things are OK?

Regards, Glenn Horrocks
  Reply With Quote

Old   January 24, 2008, 20:14
Default Re: Turbulant airflow behind 2D airfoil
  #9
Farid
Guest
 
Posts: n/a
Hi Glenn,

Thanks for your help.

Actually, I ran steady state simulation but the convergence was not very good.

For mesh quality: I made very refined hexa mesh around the airfoil(NACA0012)with the inflation layer upto 4 times the height of the airfoil and with proper Y+ value. But after that I did domain interfacing with prism mesh where for the sake of time and memory I made coarse mesh(the interfacing nodes are almost 4 times larger than those of inner hexa domain).

  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
Low Speed Airfoil Mancusi FLUENT 7 April 3, 2014 07:11
[GAMBIT] Meshing airfoil using .dat file problem creggie ANSYS Meshing & Geometry 10 June 27, 2010 20:24
Modeling Backflow for a 3D Airfoil (Wing of Finite Span) Josh CFX 9 August 18, 2009 12:31
Airfoil boundary condition Frank Main CFD Forum 1 April 21, 2008 19:36
Laminer and turbulant airfoil flow M. Essuri FLUENT 3 November 3, 2006 15:14


All times are GMT -4. The time now is 10:03.