Entrance and Exit Interactions for High-Incidence Flat Plates Encountering Finite Channels

The lift and flow interactions of a high-angle-of-attack, flat-plate wing moving through a finite-length rectangular channel are examined using force measurements and particle image velocimetry in a water towing tank. The wing translates from rest with a 45 deg angle of attack, with a tip-vortex-suppressing end condition, through 2-and 3-chord-height channels. In the channel, lift peaks associated with leading-edge vortex (LEV) formation are much larger and occur earlier after the first peak, from wing-in-channel blockage enhancing the flow speed and LEV circulation and causing faster shedding. The lift rises ahead of the channel, mainly from the impending blockage increasing the flow speed in front of the wing. The LEVs and trailing-edge vortices (TEVs) induce opposite-sign vorticity at the channel walls. If the wing exits near a lift peak (attached LEV), the next peak is much lower, whereas exiting during a minimum (LEV shedding) causes a higher subsequent peak. For the former, the LEV induces an intense, opposite exit-corner vortex that, along with the TEV, acts to break up the LEV, leaving a strong TEV that weakens the next LEV and lift peak. Rounded exit corners, a longer wing approach to the channel, and a free-tip comparison are also studied.