I'm an aerospace engineering student,and just did an aerodynamics lab in which we measured the lift & drag of a delta airfoil inside a wind tunnel between 0 and 40 degrees, in 5 degree increments, at two flow velocities (subsonic, M< 0.5). For some reason, the lift co-efficient is .25 lower throughout the entire curve in the higher velocity run compared to the lower velocity run, despite the drag co-efficient s being identical until the stall region (which begins at 30 degrees and completely separates at 35). Why is this? Considering the nature of the lab, this seems what I should be discovering. I have a theory that it has something to do with stronger vortices generated by faster flows, but wouldn't that INCREASE lift by dropping the pressure on top of the wing further?
In addition, another oddity: the L vs D curve increases SHARPLY between 0 and 10 degrees for both flows, but then the slope decreases after that and stays steady until the stall region. Why is that, and is that specific to delta wings?