The leading-edge vortex on a rotating wing changes markedly beyond a certain central body size

Bhat, Shantanu; Zhao, Jisheng; Sheridan, John; Hourigan, Kerry; Thompson, Mark C.

doi:10.1098/rsos.172197

Cited by 18 publications

(10 citation statements)

References 44 publications

(88 reference statements)

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“…The phase-averaged time traces of lift coefficient C L of the wing under quiescent conditions ( J Vert = 0) presented commonly known aerodynamic characteristics. These included a parabolic variation in the translation phase of the stroke accompanied with small peaks of lift created by rotational effects during the first rotation (pronation) and second rotation (supination) phases of each stroke (black line in figure 5 a ) which has been also observed by Dickinson et al [26], Wu and Sun [27] and Bhat et al [20]. The drag coefficient C D at J Vert = 0 also displayed similar features to those of C L with larger peaks of drag during the first rotation phase of the stroke (black line in figure 5 b ) which is aligned with the measurements reported in Dickinson et al [26].…”

Section: Resultssupporting

confidence: 62%

“…The velocity at the radius of gyration ( U RoG = 2 ϕ max fR RoG ) was used as the reference velocity and a Re = ρU RoG c / μ of 3600 based on U RoG and chord length was selected and kept constant in the present study. At this Reynolds number, representative of bees ( Bombus lapidarius Re = 3700) and moths ( Pieris brassicae Re = 4000) [18], LEVs play an important role in the generation of aerodynamic forces [20]. It may be hypothesized that vertical inflows will significantly interact with the formation and evolution of the LEV throughout the wingbeat by altering the effective angle of attack time history.…”

Section: Experimental Set-up and Proceduresmentioning

confidence: 99%

“…The data were phase averaged over 20 strokes and filtered using a low-pass, fourth-order, Butterworth filter with a cut-off frequency of 8 Hz which was significantly higher than the flapping frequency of the wing (0.254 Hz). A similar method was used by Nagai et al [24] and Bhat et al [20] to isolate the fluid mechanic forces in a Reynolds-scaled apparatus. FxL,yL false(normalsensorfalse)=FxL,yL false(normalfluid normalmechanic false)+FxL,yL false(normalweightfalse)+FxL,yL false(normalinertiafalse)and2em2em2emFxL,yL false(normalfluid normalmechanic false)=FxL,yL false(normalsensorfalse)−FxL,yL false(normalweightfalse)−FxL,yL false(normalinertiafalse),} [4pt1em<...>…”

Section: Experimental Set-up and Proceduresmentioning

confidence: 99%

“…The images were captured at the centre of the translation phase (middle of the stroke) with the light sheet positioned at the R RoG . Mid-stroke and R RoG were selected for DPIV as the LEV could be clearly observed at this location, without LEV breakdown [25] or bifurcation [20]. Due to the presence of strong chordwise flow, most of the particle motion was along the illuminated plane, and the effects of out-of-plane motion were lessened by reducing image exposure during frame acquisition, still ensuring an acceptable signal-to-noise ratio.…”

Section: Experimental Set-up and Proceduresmentioning

confidence: 99%

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Effects of uniform vertical inflow perturbations on the performance of flapping wings

et al. 2021

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Flapping wings have attracted significant interest for use in miniature unmanned flying vehicles. Although numerous studies have investigated the performance of flapping wings under quiescent conditions, effects of freestream disturbances on their performance remain under-explored. In this study, we experimentally investigated the effects of uniform vertical inflows on flapping wings using a Reynolds-scaled apparatus operating in water at Reynolds number ≈ 3600. The overall lift and drag produced by a flapping wing were measured by varying the magnitude of inflow perturbation from J Vert = −1 (downward inflow) to J Vert = 1 (upward inflow), where J Vert is the ratio of the inflow velocity to the wing's velocity. The interaction between flapping wing and downward-oriented inflows resulted in a steady linear reduction in mean lift and drag coefficients, C ¯ L and C ¯ D , with increasing inflow magnitude. While a steady linear increase in C ¯ L and C ¯ D was noted for upward-oriented inflows between 0 < J Vert < 0.3 and J Vert > 0.7, a significant unsteady wing–wake interaction occurred when 0.3 ≤ J Vert < 0.7, which caused large variations in instantaneous forces over the wing and led to a reduction in mean performance. These findings highlight asymmetrical effects of vertically oriented perturbations on the performance of flapping wings and pave the way for development of suitable control strategies.

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Section: Resultssupporting

confidence: 62%

Section: Experimental Set-up and Proceduresmentioning

confidence: 99%

Section: Experimental Set-up and Proceduresmentioning

confidence: 99%

Section: Experimental Set-up and Proceduresmentioning

confidence: 99%

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Effects of uniform vertical inflow perturbations on the performance of flapping wings

et al. 2021

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“…There was a slight change in the Re value due to the difference in the petiole distance b 0 between the two studies. This b 0 contributes to the location of the radius of gyration, affecting the calculation of the lift [48], the Rossby number [50,51], and the stability of the LEV [51].…”

Section: Validation Of the Measurement Systemmentioning

confidence: 99%

Aerodynamic performance of flexible flapping wings deformed by slack angle

Addo-Akoto

Han

2020

Bioinspir. Biomim.

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Wing flexibility is unavoidable for flapping wing flyers to ensure a lightweight body and for higher payload allowances on board. It also effectively minimizes the inertia force from high-frequency wingbeat motion. However, related studies that attempt to clarify the essence of wing flexibility remain insufficient. Here, a parametric study of a flexible wing was conducted as part of the effort to build an aerodynamic model and analyze its aerodynamic performance. The quasi-steady modeling was adopted with experimentally determined translational forces. These forces were determined from 84 flexible wing cases while varying the angle of attack at the wing root α r and the flexibility parameter, slack angle θ S, with 19 additional rigid wing cases. This study found α r for optimum lift generation to exceed 45° irrespective of θ S. The coefficient curves were well-fitted with a cubed-sine function. The model was rigorously validated with various wing kinematics, giving a good estimation of the experimental results. The estimated error was less than 5%, 6%, and 8% for the lift, drag, and moment, respectively, considering fast to moderate wing kinematics. The study was extended to analyze the pure aerodynamic performance of the flexible wing. The most suitable wing for a flapping-wing micro-aerial vehicle wing design with a simple vein structure was found to be the 5° slack-angled wing. The inference from this study further shows that a small amount of deformation is needed to increase the lift, as observed in natural flyers. Thus, wing deformation could allow living flyers to undertake less pitching motion in order to reduce the mechanical power and increase the efficiency of their wings.

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