Negative drag in generalExternalFlow

Dear all,

I’m using the basic generalExternalFlow code example to simulate the flow around a wing and I get generally speaking satisfactory results. Nevertheless, it returns me sometimes negative drag for some wing geometries and I don’t understand why because the visualizations of the flow are very similar to simulations for which the drag force was positive.

Is there something I am missing about force projection or something ? Is it due to the .stl I use ? Or the normalSurface function ?

Thanks in avdance for your help,


This seems strange but it’s very difficult to tell. Could you post the flow and the drag you get?