Abstract
A sweptback angle can directly regulate a leading-edge vortex on various aerodynamic devices as well as on the wings of biological flyers, but the effect of a sweptback angle has not yet been sufficiently investigated. Here, we thoroughly investigated the effect of the sweptback angle on aerodynamic characteristics of low-aspect-ratio flat plates at a Reynolds number of 2.85 × 104. Direct force/moment measurements and surface oil-flow visualizations were conducted in the wind-tunnel B at the Technical University of Munich. It was found that while the maximum lift at an aspect ratio of 2.03 remains unchanged, two other aspect ratios of 3.13 and 4.50 show a gradual increment in the maximum lift with an increasing sweptback angle. The largest leading-edge vortex contribution was found at the aspect ratio of 3.13, resulting in a superior lift production at a sufficient sweptback angle. This is similar to that of a revolving/flapping wing, where an aspect ratio around three shows a superior lift production. In the oil-flow patterns, it was observed that while the leading-edge vortices at aspect ratios of 2.03 and 3.13 fully covered the surfaces, the vortex at an aspect ratio of 4.50 only covered up the surface approximately three times the chord, similar to that of a revolving/flapping wing. Based on the pattern at the aspect ratio of 4.50, a critical length of the leading-edge vortex of a sweptback plate was measured as ~3.1 times the chord.
Highlights
IntroductionAcademic Editors: Hoon Cheol Park and Guido de Croon
The exceptional maneuverability required for the vehicles, e.g., vertical takeoff/landing, stable hovering, and smooth transition to forward flight, provokes separated flows with a complicated interaction in shed vortices at low Reynolds number
We found a resemblance in aerodynamic characteristics to that of a revolving/flapping wing, which is presumably due to an analogous behavior of the two leading-edge vortex (LEV)
Summary
Academic Editors: Hoon Cheol Park and Guido de Croon. Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. State-of-the-art aerial vehicles such as personal air vehicles, flying cars, drones, and micro/nano air vehicles do have their unique shapes creating a fully three-dimensional flow. The exceptional maneuverability required for the vehicles, e.g., vertical takeoff/landing, stable hovering, and smooth transition to forward flight, provokes separated flows with a complicated interaction in shed vortices at low Reynolds number. These severely affect the aerodynamic performance overall; a thorough investigation of the separated flows is a crucial step for the appropriate development
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