`DuSeligEggers` and negative drag coefficients about ccblade.jl HOT 5 OPEN

The physics is quite tenuous for this method. Seems like this should be fine to change.
I assume this means that you are changing the airfoil shape during the optimization? If not, I'd definitely use precomputed polars rather than on-the-fly ones.

from ccblade.jl.

I assume this means that you are changing the airfoil shape during the optimization? If not, I'd definitely use precomputed polars rather than on-the-fly ones.

Actually I am using precomputed polars. I create a single CCBlade.jl airfoil struct and use the same Reynolds correction, hub/tip correction, mach number correction, and rotation correction structs for the entire optimization. It appears the optimizer is able manipulate the inputs to the rotation correction in a way that reduces the drag to < 0, despite the DuSeligEggers parameters (a, b, d, m, alpha0) never changing.

from ccblade.jl.

Ah, I mean I always precompute the rotational corrections also.

from ccblade.jl.

This is common practice in the wind energy field. Rotational and other corrections (including extrapolation), especially when combined together can easily go off the rails. So we always create fully precomputed polars. This does mean that you have to apply the rotational correction at a notional section (typically around 70% radius as that is around the midpoint of the blade based on area). The corrections are semi-empirical and can't really be justified all the way towards the root and towards the balde.

from ccblade.jl.

Gotcha, thanks for the explanation. I see there's an example of precomputing the rotational correction in the docs: https://flow.byu.edu/CCBlade.jl/stable/howto/#Airfoil-Data. I'll give that a shot in the future.

from ccblade.jl.