[devanson]

Dear Friends,
I need your help. Currently, I am doing a CFD validation cases on 2D airfoil at low Reynolds number (Range 50,000 to 200,000).

Airfoil chosen : S1223 (available on www.airfoiltools.com)
Reynolds no : 200,000
Mesh : Structured mesh using ICEM CFD (With boundary layer mesh having first cell height of y+=1)
Solver : ANSYS Fluent
Turbulence Model : Spallart-Allmarus

The problem is the lift curve (Coefficient of lift vs angle of attack) is way off from Experimental curve). Max Cl (Coefficient of lift) is supposed to be 2.3 at angle of attack 15. But I am getting 1.9 at 13 degree.

Another case: with Flat plate. My Max Cl is deviating away from Experiment value. But the Drag and moment curve are matching close to experiment.

Why I am getting this deviation? Is there a good approach to deal with Low Re flow?

[kesari]

Hey Dinesh,

As a part of my project I had done an exhaustive analysis of NACA4421 airfoil and also checked NACA0012 airfoil.

I found out that however good the ICEM CFD mesh is, it consistently underestimates the Cl values by 10% compared to an ANSYS mesh. I still haven't figured out why but this seemed to be the case for all RANS 2 equation turbulence models.

This might be the same problem you are facing. Try it with a good mesh generated with the help of ANSYS Meshing and check if it's still underestimated.

Will update as soon as I figure out a solution.

Cheers,
Sriram

[Tushar K Herle]

Hi,
Actually i am also working on the same S1223 aerofoil, nearly same renolds number and same model. I ve used a mesh generated using Gambit. It is hybrid mesh with quadrilateral mapped mesh around the aerofoil and free mesh in far field. Even i am facing the same problem.
At small angle of attack i am getting the same values as xfoil but as the angle of attack increases the deviation from the xfoil values too is increasing..

-Tushar

[farzadpourfattah]

hi.
i suggest you use Transition kw (4 equations) model in fluent for modeling Low Reynolds number, I validate flow around SD8020 with experiment data in different AOAs.

[devanson]

Hi Friends,

Still facing the same issues? Any solutions?

I tried with K-O 4 equations & V2F. Facing difficulties in converging the solutions. :-(

[farzadpourfattah]

yes good convergence depend on boundary layer mesh.
can you detect the bubbles on airfoil?

[devanson]

I created a vry fine mesh with wall y+ <=1. But still facing the issue. Using S-A, case is converged. But Lift & drag values differ from Windtunnel data.

[farzadpourfattah]

hi
change your Turbulence model to Kw-sst or Transition kw (4 equations) model.

[AidealZohary]

Hi, this is an old thread. But if anyone is still interested to run a simulation on the S1223 airfoil, please take a look at:

Numerical Investigation on the Pressure Drag of Some Low-Speed Airfoils for UAV Application.
https://doi.org/10.37934/cfdl.13.2.2948

Unsteady 3-equation k omega intermittency SST was used. Good comparison with XFOIL and experimental data. Transition features also shown through cf and cp plots.

[AidealZohary]

Originally Posted by AidealZohary

Hi, this is an old thread. But if anyone is still interested to run a simulation on the S1223 airfoil, please take a look at:

Numerical Investigation on the Pressure Drag of Some Low-Speed Airfoils for UAV Application.
https://doi.org/10.37934/cfdl.13.2.2948

Unsteady 3-equation k omega intermittency SST was used. Good comparison with XFOIL and experimental data. Transition features also shown through cf and cp plots.

Learn how I designed the mesh here:

https://www.youtube.com/watch?v=qZRqBu9Ss2U