Lift and Drag Numbers seem off on a 3D Airfoil!

Hey all I am new here.

I’m trying to run a CFD simulation of my airfoil at varying angles of attack at 45 meters per second. My numbers are stabilizing after a few iterations for the Lift and Drag Coefficients and the Force Plots but the numbers just seem off to me.

The Drag Coefficient is going down as my Angle of Attack is going up which makes no sense to me. My Lift numbers also seem off.

The Force Plots are also showing a number I would expect to see for Pressure Force in the Z (Downforce) but the Pressure Force in the Y (Drag) seems really low.

Screen Shot 2021-03-05 at 7.51.01 AM
Downforce and Drag are in lbf for the entire airfoil in this picture.

Here’s a link to my project:
Airfoil Design

Seriously any help you all can offer is appreciated. I’ve been racking my brain on this one for days.



Hi Ryan, this is Fillia :slight_smile:
The first thing I noticed about the project is the mesh and the sizing of the domain, so to begin with, I suggest you use the sizing (check Figure 6) according to this tutorial: Wing Simulation: Compressible Flow Around a Wing | SimScale Tutorial
Keep in mind that you need to adjust the dimensions to the characteristics of your own model.

Also, I see that you used the same settings, but these have to be adjusted as well. As you might have noticed, the region refinements have a big maximum length size limitation, so they have no impact on the generated mesh:

The quality of the mesh can be very important for the results, as well as the y+ values:

After you refine the mesh and rerun, let me know about the new results :slight_smile:

Best regards,

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Thanks! I’ll re-run this evening and update here.