Evolution of the Leading-Edge Vortex over an Accelerating Rotating Wing

AbstractThe flow field over an accelerating rotating wing model at Reynolds numbers Re ranging from 250 to 2000 is investigated using particle image velocimetry, and compared with the flow obtained by three-dimensional time-dependent Navier-Stokes simulations. It is shown that the coherent leading-edge vortex that characterises the flow field at Re~200-300 transforms to a laminar separation bubble as Re is increased. It is further shown that the ratio of the instantaneous circulation of the leading-edge vortex in the accel-eration phase to that over a wing rotating steadily at the same Re decreases monotonically with increasing Re. We conclude that the traditional approach based on steady wing rotation is inadequate for the prediction of the aerodynamic performance of flapping wings at Re above about 1000

Leading-edge vortex shedding from rotating wings

International audienceThe paper presents a numerical investigation of the leading-edge vortices generated by rotating triangular wings at Reynolds number Re=250. A series of three-dimensional numerical simulations have been carried out using a Fourier pseudo-spectral method with volume penalization. The transition from stable attachment of the leading-edge vortex to periodic vortex shedding is explored, as a function of the wing aspect ratio and the angle of attack. It is found that, in a stable configuration, the spanwise flow in the recirculation bubble past the wing is due to the centrifugal force, incompressibility and viscous stresses. For the flow outside of the bubble, an inviscid model of spanwise flow is presented

Complete wing chordwise z=0.25

PIV measurements of the complete wing at z=0.25 at all tested angles of attac

Data from: Hovering hummingbird wing aerodynamics during the annual cycle

The diverse hummingbird family (Trochilidae) has unique adaptations for nectarivory, among which is the ability to sustain hover-feeding. As hummingbirds mainly feed while hovering, it is crucial to maintain this ability throughout the annual cycle—especially during flight-feather moult, in which wing area is reduced. To quantify the aerodynamic characteristics and flow mechanisms of a hummingbird wing throughout the annual cycle, time-accurate aerodynamic loads and flow field measurements were correlated over a dynamically scaled wing model of Anna’s hummingbird (Calypte anna). We present measurements recorded over a model of a complete wing to evaluate the baseline aerodynamic characteristics and flow mechanisms. We found that the vorticity concentration that had developed from the wing’s leading-edge differs from the attached vorticity structure that was typically found over insects’ wings; firstly, it is more elongated along the wing chord, and secondly, it encounters high levels of fluctuations rather than a steady vortex. Lift characteristics resemble those of insects; however, a 20% increase in the lift-to-torque ratio was obtained for the hummingbird wing model. Time-accurate aerodynamic loads were also used to evaluate the time-evolution of the specific power required from the flight muscles, and the overall wingbeat power requirements nicely matched previous studies

Complete wing chordwise z=0.5

PIV measurements of the complete wing at z=0.5 at all tested angles of attac

P10 wing chordwise z=0.75

PIV measurements of the P10 wing at z=0.75 at all tested angles of attac

P89 wing spanwise

PIV measurements of the P89 wing at all tested angles of attac

Complete wing spanwise

PIV measurements of the complete wing at all tested angles of attac

P1-4 wing chordwise z=0.5

PIV measurements of the P1-4 wing at z=0.5 at all tested angles of attac

Aerodynamic loads

Aerodynamic loads for all tested wing