Difference between Fx in Flow5 & XFLR5

Tom asked 3 months ago

I have opened an xflr5 model in flow5 and re-run the analysis.
The plot for Fx vs V is completely different between the two programs, while everything else appears to be the same…
The Fx vs V plot in xflr5 is as expected (looks roughly like an x^2 curve) while the Fx vs V plot in flow5 seems wrong (looks more like an x^0.5 curve)
Is Fx calculated for a different coordinate system in flow5 compared to xflr5? Am I missing something?

André Deperroistechwinder Staff replied 3 months ago

It seems indeed that there is an issue with the calculation of the forces. I’ll investigate and post back.
André

André Deperroistechwinder Staff replied 3 months ago

The problem is that the Fx_FF variable in flow5: (1) only includes the induced part of the drag, and (2) is given in geometric/body axes and not in wind axes.
This was a design choice for the alpha phase, but is has no reason to be anymore. It will be corrected in beta 08 so that the results match those of xflr5.
André