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

High Lift Airfoils At High Angles Of Attack

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

Like Tree1Likes
  • 1 Post By Luiz Pancini

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   April 6, 2015, 08:22
Post High Lift Airfoils At High Angles Of Attack
  #1
New Member
 
Luiz Pancini
Join Date: Jan 2015
Posts: 3
Rep Power: 8
Luiz Pancini is on a distinguished road
Hello,

I've been trying to simulate high lift airfoils generated by an airfoil optimizer program, ranging from negative angles of attack (AoA) to stall, at low Reynolds number (250 thousands) using Fluent.

In order to validate my results, I have simulated a well known high lift airfoil, the Selig 1223.

Though my cl, cd and cm results are accurate enough at low and medium angles of attack (i.g. from -2 to 12), I was unable to get reasonable values at +12. Fluent underpredicts both the angle of stall and maximum cl, while overpredicting cd.

I know that drag overpredictions are common, besides, I am using a turbulent model, while the wind tunnel tests contain at least some laminar flow. But, I still would expect a better value for the cl, even at these high angles of attack.

Now, about the settings:

I have tried the pressure-based Spalart-Allmaras (SA), k-e, k-w, and even SST. My best results came from SA, while in many cases SST didn't even converge. I tried both steady and transient, transient came up a bit better in some cases, Second Order Upwind, Third-Order Muscl and Quick formulations, all give about the same results.

I used a very fine 2D C-grid, with 1.97 million cells, y+ lower than 1 everywhere in the airfoil. Maximum aspect ratio of 916 and minimum orthogonal quality of 0.67. I did it the in ICEM, the way Simon shows in this youtube tutorial: https://www.youtube.com/watch?v=tYrbScUH9RE. Here goes some pictures of it:

http://s18.postimg.org/oasua5uzd/icem_mesh.png
http://s3.postimg.org/rum73srs3/leading_edge.png

For the SA model, the drag sensitivity to the domain extent showed that at 60 chords the values deviated up to 10% at medium AoA, while lift was up to 5% discrepancy, even for a 15 chord. For a 15 chord domain, lift results were off by a maximum of 3%, until 12 AoA.

If anyone knows how to improve the solution at high AoA (including stall), which is my main objective, I would really appreciate your help.
Maze likes this.
Luiz Pancini is offline   Reply With Quote

Old   April 8, 2015, 20:57
Default
  #2
New Member
 
Join Date: Jan 2015
Posts: 1
Rep Power: 0
Maze is on a distinguished road
The problems solved?
Maze is offline   Reply With Quote

Old   April 9, 2015, 08:01
Default
  #3
New Member
 
Luiz Pancini
Join Date: Jan 2015
Posts: 3
Rep Power: 8
Luiz Pancini is on a distinguished road
Not yet. Trying some 3D now.
Luiz Pancini is offline   Reply With Quote

Reply

Tags
airfoil, lift and drag, mesh 2d, spalart allmaras, stall

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
Airfoils and lift compared to air density and TE Jens Main CFD Forum 0 May 4, 2006 03:31
High Lift Devices Anshul Main CFD Forum 5 June 21, 2005 07:10
High Angle of Attack w0er Main CFD Forum 3 March 8, 2005 11:05
High lift analysis using overset kei-tee Main CFD Forum 0 April 10, 2003 09:53
grids around airfoils at high aoa uygun Main CFD Forum 9 October 11, 2002 08:30


All times are GMT -4. The time now is 14:24.