[Avraham]

Hi everybody, I am new to this site and this is my first post here.

I have been doing the Cornell University Tutorials regarding 2D Fluent steady state turbulance analysis of a NACA airfoil and using the Ansys student workbench package.

All settings are as per tutorial; Mesh quality, Convergence quality, Velocity, input and output expressions etc...

My question is related to the Cl readings...

As my AoA is increased beyond 10degree the Cl reading keeps increasing when it should actually be decreasing... Can somebody please tell me what am I missing here?!

The Velocity_Inlet direction is fixed in X direction and I am augmenting the AoA of the airfoil via design point table input.

The output data for Lift Drag Cl Cd and moment are aligned with NASA results, however as the AoA is increased I am not seeing any falloff of the Cl?! What could be the cause of this?

Appreciate any help here, thanks....

[LoGaL]

which turbulence model did you choose?

[Avraham]

Thanks for the response!

I have tried a few turbulence models - K-epsilon, K-omega, Spalart Allmaras (SST)... they all converge and provide similar results; Spalart Allmaras demonstrates boundary layer separation best, and my Y+ is currently at 35... None of the turbulence models demonstrate a fall-off of Cl with increased AoA.. I am thinking to try meshing in ICEM to get the Y+ to below 1

[LoGaL]

So wait, do you have tetra grid with Y+=30 around the airfoil? If you want to predict stall, that is garbage, if you ask me
Are you at least using inflation layers? If yes, why dont' you set the first layer height to get y+ = 1 and use K-omega SST? And, by the way, since you speak about NASA results, i presume this is a standard naca airfoil, so you can fit a lot of inflation layers around the airfoil (30-40)

And Spalart Almaras SST does not exist man, either it is Spalart Almaras or K-omega SST. The former is bad to predict stall, the latter requires Y+ = 1. Anyhow my call is to improve your mesh, I can confirm it if you posyt a picture of it

[Avraham]

Thanks for the feedback LoGal... Yes, was K-Omega SST and Spalart Almaras... I will follow your advice and use inflation layer correctly at Y+1 and see what happens and post the results... Should I leave Energy option checked or unchecked for this kind of analysis? ��

[LoGaL]

Hi Avraham, depends if your flow is compressible or not, which in turn depends on the mach number of the flow. Just leave it on anyways, it won't harm
BTw, you are not showing me a pic of the mesh