I was recently asked if there are fundamental flow phenomena that would benefit from further wind tunnel evaluation. I was able to come up with the following phenomena. 1) There's an old naca report on helicopter rotor tested in descending axial flow in a wind tunnel, and that data does not appear to be consistent with current simulations. Some colleagues suggest that the data is wrong, or, that discrepancy may indicate a area for further investigation into the basic flow phenomena. 2) An area that I don't see a lot of work on is reverse flow airfoils with leading/trailing edge slats/flaps. But that problem may just be a difficult simulation / design problem, and not really a flow phenomena problem. 3) I was looking at some CFD trends of lift and drag with Reynold's number between 1 to 6 million, and I'm not sure those trends have been validated with test data. 4) There's some recent work on blowing / suction airfoil tests, with blowing / suction alternating from top/bottom along the span. There appears to be additional benefit from alternating from top to bottom, and I'm not sure anyone expected that result. Are there additional aerodynamic phenomena that would benefit from further investigation?