High-Angle-of-Attack Translating Wings Interacting with Finite Channel Obstacles

Force and flow-field measurements are done in a water towing tank to understand the time-varying lift and vortex dynamics of a high-angle-of-attack, flat-plate wing encountering finite-length channel obstacles. The wing starts from rest and translates with a 45° angle of attack, and its leading edge reaches the channel at 1 chord of travel. In the wing frame, it is centered vertically between the upper and lower channel walls. The streamwise channel length and height between the streamwise walls is varied. To simplify the interactions and reduce wingtip effects, a<2% chord gap between the tip and bottom tank wall is used. The lift peaks, associated with leading-edge vortex (LEV) formation and shedding, are much larger when the wing is in the channel. Also, for the second peak and afterward they occur earlier even past the channel exit. These results are from the blockage of the wing in the channel that increases the flow speed around it. There is a lift rise prior to the channel entrance, which serves as a “warning” ahead of it. The lift loss after the channel depends on whether exiting is done during a lift peak or minimum. For the latter, the subsequent peak may be as low as, or below, the no-obstacle case. Vorticity fields from planar particle image velocimetry (PIV) show that the channel LEVs have greater circulation and the earlier timing mentioned, consistent with the forces. The LEVs induce secondary, opposite-sign vorticity on the upper channel surface and the entrance and exit corners, which weakens the LEVs but does not offset the overall substantial lift increases. Interactions with the trailing-edge vortices (TEVs) are also discussed.