SimScale CAE Forum

Drag Coefficient off


I am trying to reduce the drag coefficient of a CAD model by adding holes in the wheelhouse.
The CAD model is inspired from the Audi A7, there are three model, the original one with no modifications, a first modified model with holes and a second model with holes located at different positions. The projects are named respectively Original CAD Assembly, CAD Assembly 1 and CAD Assembly 2.

The drag coefficient of an actual Audi A7 is 0.27 according to the manufacturer. With the two modified CAD model I manage to get 0.24-0.25 which is not too far from the actual model.
The problem is that my original model, which is supposed to be my source of comparison has a drag coefficient of 0.19, which is not too off from the real one but compared to the other two CADs it is a bit far off.
The three models have the same mesh and same settings (apart from the last runs since I tried to find the source of the offset)

However, the models do not have exactly the same dimensions even after scaling, but they are still quite close to each other.
I was wondering where this offset could come from.

Thank you,


Hi @vwirth!

I saw that the scaling is still not correct though, you have illegal cells in your mesh and the geometry looks kind of odd to me (wavy structure). @cfd_squad - can you comment on the setup of our user?




Hi @vwirth ,

Your calculation of Cd 0.19 has not converged, so the result is not correct.

In addition, your setting of “Lift direction” should be [ 0, 0, 1 ], not [ 0, 1, 0 ] .