The Unsteady Lift Produced by a Flat-Plate Wing Translating Past Finite Obstacles

TL;DR

This study investigates how finite obstacles like channels, ceilings, and grounds affect the unsteady lift of a high-angle-of-attack flat-plate wing using towing-tank measurements, revealing obstacle-specific effects on vortex dynamics and lift peaks.

Contribution

It provides new experimental insights into the unsteady lift behavior of wings near finite obstacles, highlighting the influence of obstacle geometry and positioning on vortex formation and lift variation.

Findings

Circulatory lift peaks are largest with smaller gap heights in channels.

Lift decreases when exiting a channel, especially during lift peaks.

Ground effects minimally influence peak timing, indicating reduced impact on LEV dynamics.

Abstract

The unsteady lift of a high-angle-of-attack, flat-plate wing encountering finite-length obstacles is studied using towing-tank force measurements. The wing translates from rest and interacts with a rectangular channel, ceiling, or ground obstacle. Variations with angle of attack, obstacle length, mid-chord height to the obstacle, and starting distance between the wing leading edge (LE) and obstacle (typically 1 chord) are examined. For channels, as the gap height decreases, circulatory-lift peaks attributed to leading-edge vortices (LEVs) are the largest, and from the second peak onward occur earliest. This is likely from wing blockage enhancing the flow speed. The lift reduces while exiting a channel, and is lowest afterward if exiting during a lift peak. For ceilings, the first circulatory-lift maximum increases for smaller LE-to-ceiling gaps, but for gaps of 0.5 chords or less, subsequent peaks are below the no-obstacle case yet still earlier. For grounds, with lower wing height the first circulatory-lift peak is larger but the second peak's behavior varies with angle of attack, and the lift decreases near the ground end. Grounds affect peak timing the least, indicating a reduced influence on the LEV. Changing the starting distance to a channel alters the lift, likely from different LEV timing.