CFD Online Logo CFD Online URL
Home > Forums > Software User Forums > ANSYS

Airfoil validation issues - Cl not correct

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

LinkBack Thread Tools Search this Thread Display Modes
Old   January 8, 2023, 08:45
Unhappy Airfoil validation issues - Cl not correct
New Member
Join Date: Aug 2021
Posts: 25
Rep Power: 3
cons013 is on a distinguished road
I am trying to validate an s1223 airfoil vs experimental data found here:

I am trying to do this in 2d and 3d to compare results and speed, for the purposes of comparing turbulence models. My 3d model consists of a wing with two symmetry walls at either side, with two no shear walls above and below, using Re=200,000. The 2d model is an unstructured tet mesh and all simulations are steady state with second order schemes.

In 3D, am noticing that the k-w sst model is underpredicting lift compared to k-e, and for some reason k-w sst does not handle post stall properly at all. The lift figures nosedive after 13 degrees aoa and I don't see why this would happen. 2D is even worse, even pre-stall the omega sst model is underpredicting lift by a long way, whereas k-e is showing good convergence. I have ensured y+ of less than 1 with sufficient prism growth, but nothing works.

I noticed that, in 3D, if my mesh is too fine, convergence isn't achieveable. I coarsened the mesh to see if this would artifically dampen any vortex shedding at 13 degrees and it worked well, giving a Cl of around 2. To test if this would help further, I tried again using these same mesh settings at 18 degrees, expecting a Cl of around 2.1, but ended up with around 1.55. Again k-e gave a much better result at around 1.8.

I am very confused here, what could be going wrong? Experimental data shows stall at around 19 degrees, yet the CFD is giving me much earlier stall. Am I just wasting my time trying to get steady-state convergence here, considering that around stall we will have shedding and other transient effects happening? What confuses me is the sheer difference with k-e and k-w sst. I had believed that the omega sst model was better and predicting and handling separation, but my results show this to not be the case. What could I be doing wrong??
cons013 is offline   Reply With Quote


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
Problem with restart solution in robyTKD SU2 Shape Design 21 May 29, 2013 10:26
Convergence Issues 2D Airfoil AeroEngiNerd STAR-CCM+ 1 February 28, 2012 10:34
CFX-Pre problem, pls help!!! cth_yao CFX 0 February 17, 2012 01:52
Airfoil boundary condition Frank Main CFD Forum 1 April 21, 2008 19:36
Airfoil y+ for Validation Purposes asd FLUENT 3 June 26, 2007 10:27

All times are GMT -4. The time now is 00:53.