Interplay of the leading-edge vortex and the tip vortex of a low-aspect-ratio thin wing

Three-dimensional vortical structures and their interaction over a low-aspect-ratio thin wing have been studied via particle image velocimetry at the chord Reynolds number of $$10^5$$ 10 5 . The maximum lift of this thin wing is found at an angle of attack of $$42^\circ$$ 42 ∘ . The flow separates at the leading-edge and reattaches to the wing surface, forming a strong leading-edge vortex which plays an important role on the total lift. The results show that the induced velocity of the tip vortex increases with the angle of attack, which helps reattach the separated flow and maintains the leading-edge vortex. Turbulent mixing indicated by the high Reynolds stress can be observed near the leading-edge due to an intense interaction between the leading-edge vortex and the tip vortex; however, the reattachment point of the leading-edge vortex moves upstream closer to the wing tip. Graphic abstract

The Effects of a Passively Actuated Trailing Edge on the Aerodynamics of an Oscillating Wing

This study examines the use of a passively actuated trailing edge of a thin wing during oscillation motion. The integration of a flexible trailing edge with an oscillating wing has the ability to alter the transient lift and drag characteristics, as well as the time averaged values. The results are obtained for a chord-length based Reynolds number of 0 and 40,000, and at oscillation frequencies of 0.5 and 1 Hz. The non-dimensional heaving amplitude is fixed at 0.25 and the pitching is 20°. The flexibility of the trailing edge is controlled by a torsion rod between the main wing and the trailing edge. Three conditions are evaluated: a very stiff rod (essentially non-flexible trailing edge), a moderately flexible rod and a very flexible rod. Results obtained indicate that lift and drag have a shift in the time averaged values, where the drag and lift both decrease as the trailing edge flexibility increases. These findings have application to both enhanced propulsion and energy harvesting.