Harry:
You were talking about a highly separated flow regime. That's (in the context of this case) the low speed regime stall. The case under discussion isn't, as far as I understand, a high speed (and thus high mach for this airplane) stall example.
Yes and when in a highly separated flow regime (fully stalled foils), extreme AoA, we may typically dispense with the assumption we are flying, per se, and often revert to just summing the Resultant Force vectors rather than thinking in terms of Cl, Cd and Cm, associated with the fairly linear ranges of the lift curve slope and pitching moment slope (Cd just about remains a mashup of a parabola and drag dropout buckets at high Mach)
I wasn't sure what to make of your reference to high mach, honestly.
That's why I asked. I think, on reading your post again, you were comparing shapes of Cd curves at different ends of the spectrum ... as a general reference?
What do you mean by high Mach ? > M 0.5? transonic? or supersonic?
In the context of this class of airfoil (large transport) let's say transonic or approaching supersonic (limits of airfoil before the high speed buffet, coffin corner, etc.) would seem to me "high mach" as the airfoil isn't shaped for operations in supersonic flight. (I confess, it's been over thirty years since I studied compressible flow, and things like Prandtl Meyer flow, so it doesn't recall well from memory.)
I don't think we'd get anywhere discussing this airfoil under conditions at Mach 2, for example.
