Effect of Approach Distance on Flat-Plate Wings Encountering Finite Channel Obstacles

The effect of a high-angle-of-attack flat-plate wing’s approach distance to a finite-length channel on the unsteady lift is studied in a water towing tank. The no-obstacle (NO) case is acquired, and the leading-edge vortex (LEV) related peaks decay to be more periodic past 20 chords in translation. The wing reaches the channel afterward, and different approach distances are chosen so the wing enters it near LEV pinch-off, LEV shedding with trailing-edge vortex (TEV) growth, and LEV formation. At Reynolds number 6,000 and 45 degrees angle of attack, the gap-height and length of the channel are varied to examine their effects. The blockage from the channel gives a “warning” ahead of it by raising the lift for all cases. Further, the blockage causes higher lift and vortex shedding frequency in the channel. The smallest approach distances, where the LEV forms fully in the channel, yield the largest first lift peak from greater blockage enhancement, whereas entering with an already-growing LEV gives the lowest. For the narrow channel, the interaction causes a set of decreasing peaks after the initially high one; the wider channel gives the opposite behavior. Past the exit, the lift reduces but is still larger than for NO.