Week 6, Day 2:
Today was the first day of project 3, in which we collected wind tunnel force balance data for two finite NACA 4412 wings of different aspect ratios across a sweep of angles of attack.
We added 3 tufts at spanwise locations varying from near the center to near the tip on the suction side of the wings in order to attempt to visualize the progression of stall from root to tip. On the lower aspect ratio wing, we were reasonably successful: the centermost tuft indicated a well-developed stall several degrees of AoA earlier than the tip tuft. In fact, the tip tuft on this wing nearly never gave the traditional fully separated flow stall indication due to interactions with the tip vortex.
Despite the use of the same airfoil section, the higher aspect ratio wing stalled much earlier and, based on observations of the tufts, more thoroughly than the lower aspect ratio wing. This makes sense because the manifestation of the differences in stall angle by spanwise location are a result of the finite-ness of the wing, so since the lower AR wing is in some sense “more finite” than the other these effects should be more pronounced.