[AeroDuude]

Hello smart people out there,
for my Bachelor dissertation among other things, I simulate a flat plate (3D to capture the effect of the edge vortex) at AoAs from -2deg to +14deg with the following dimensions:

- chord: 470mm
- span: 107mm
- thickness: 16mm
- an elliptical leading edge
- a triangular (tapered) trailing edge

During the post processing of my first set of simulations I discovered, that the highest x-force and thus the drag force appears at 0deg AoA and decreases for both positive and negative AoAs. Actually the x-force reaches 0 at about 10deg AoA and even becomes negative for angles above 10deg.
Due to the fact that the mesh I used for this set, was not very fine and my setting not that thoughtful, I created several meshes with drastically better quality (about 5 times more nodes, very fine sizings around the plate and an inflation layer to reach a y+ value of 1). In addition to that I've read a lot about the setup and adjusted it accordingly. I even tried to define the plate as rough wall with a fitting Sand Grain Roughness.
Unfortunately this steps didn't bring the wished effect - the x-forces only changed very little and remained negative for the corresponding angles.
Maybe one of you can help me, to get a solution to this problem or at least explain this effect.

[ghorrocks]

Please post an image of what you are modelling and your output file.

Also this FAQ gives general advice: https://www.cfd-online.com/Wiki/Ansy..._inaccurate.3F

[AeroDuude]

I got it:
The equation for drag needs to be: Fx*cos(alfa)+Fy*sin(alfa).
I forgot the Fy part.