scholarly journals How oscillating aerodynamic forces explain the timbre of the hummingbird’s hum and other animals in flapping flight

eLife ◽  
2021 ◽  
Vol 10 ◽  
Author(s):  
Ben J Hightower ◽  
Patrick W A Wijnings ◽  
Rick Scholte ◽  
Rivers Ingersoll ◽  
Diana D Chin ◽  
...  
Keyword(s):  
Aerodynamic Force ◽  
Microphone Array ◽  
Flapping Wings ◽  
Acoustic Model ◽  
Acoustic Measurements ◽  
Aerodynamic Forces ◽  
Drag Forces ◽  
Radiated Power ◽  
Lift And Drag

How hummingbirds hum is not fully understood, but its biophysical origin is encoded in the acoustic nearfield. Hence, we studied six freely hovering Anna's hummingbirds, performing acoustic nearfield holography using a 2176 microphone array in vivo, while also directly measuring the 3D aerodynamic forces using a new aerodynamic force platform. We corroborate the acoustic measurements by developing an idealized acoustic model that integrates the aerodynamic forces with wing kinematics, which shows how the timbre of the hummingbird's hum arises from the oscillating lift and drag forces on each wing. Comparing birds and insects, we find that the characteristic humming timbre and radiated power of their flapping wings originates from the higher harmonics in the aerodynamic forces that support their bodyweight. Our model analysis across insects and birds shows that allometric deviation makes larger birds quieter and elongated flies louder, while also clarifying complex bioacoustic behavior.

Aerodynamics of a Rugby Ball

2012 ◽  
Vol 79 (2) ◽  
Author(s):  
A. J. Vance ◽  
J. M. Buick ◽  
J. Livesey
Keyword(s):  
Aerodynamic Force ◽  
Angular Position ◽  
Separation Point ◽  
Aerodynamic Forces ◽  
Ball Speed ◽  
Flow Visualizations ◽  
Lift And Drag ◽  
Yaw Angle ◽  
Linear Manner ◽  
Existing Data

This paper describes the aerodynamic forces on a rugby ball traveling at speeds between 5 and 15 ms−1. This range is typical of the ball speed during passing play and a range of kicking events during a game of rugby, and complements existing data for higher velocities. At the highest speeds considered here, the lift and drag coefficients are found to be compatible with previous studies at higher velocities. In contrast to these higher speed investigations, a significant variation is observed in the aerodynamic force over the range of velocities considered. Flow visualizations are also presented, indicating how the flow pattern, which is responsible for the aerodynamic forces, changes with the yaw angle of the ball. This flow and, in particular, the position of the separation points, is examined in detail. The angular position of the separation point is found to vary in a linear manner over much of the surface of the rugby ball; however, this behavior is interrupted when the separation point is close to the ‘tip’ of the ball.

scholarly journals Experimental Study on Flexible Deformation of a Flapping Wing with a Rectangular Planform

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Wenqing Yang ◽  
Jianlin Xuan ◽  
Bifeng Song
Keyword(s):  
High Speed ◽  
Aerodynamic Force ◽  
Inertial Force ◽  
Aerodynamic Characteristics ◽  
Flapping Wing ◽  
Image Correlation ◽  
Flapping Wings ◽  
Aerodynamic Forces ◽  
Cyclic Movements ◽  
Flexible Deformation

A flexible flapping wing with a rectangular planform was designed to investigate the influence of flexible deformation. This planform is more convenient and easier to define and analyzed its deforming properties in the direction of spanwise and chordwise. The flapping wings were created from carbon fiber skeleton and polyester membrane with similar size to medium birds. Their flexibility of deformations was tested using a pair of high-speed cameras, and the 3D deformations were reconstructed using the digital image correlation technology. To obtain the relationship between the flexible deformation and aerodynamic forces, a force/torque sensor with 6 components was used to test the corresponding aerodynamic forces. Experimental results indicated that the flexible deformations demonstrate apparent cyclic features, in accordance with the flapping cyclic movements. The deformations in spanwise and chordwise are coupled together; a change of chordwise rib stiffness can cause more change in spanwise deformation. A certain lag in phase was observed between the deformation and the flapping movements. This was because the deformation was caused by both the aerodynamic force and the inertial force. The stiffness had a significant effect on the deformation, which in turn, affected the aerodynamic and power characteristics. In the scope of this study, the wing with medium stiffness consumed the least power. The purpose of this research is to explore some fundamental characteristics, as well as the experimental setup is described in detail, which is helpful to understand the basic aerodynamic characteristics of flapping wings. The results of this study can provide an inspiration to further understand and design flapping-wing micro air vehicles with better performance.

scholarly journals Aerodynamic effects of flexibility in flapping wings

2009 ◽  
Vol 7 (44) ◽  
pp. 485-497 ◽  
Author(s):  
Liang Zhao ◽  
Qingfeng Huang ◽  
Xinyan Deng ◽  
Sanjay P. Sane
Keyword(s):  
Computational Models ◽  
Aerodynamic Force ◽  
Leading Edge ◽  
Flapping Flight ◽  
Force Generation ◽  
Flapping Wings ◽  
Centre Of Pressure ◽  
Aerodynamic Forces ◽  
Trailing Edge ◽  
High Angles Of Attack

Recent work on the aerodynamics of flapping flight reveals fundamental differences in the mechanisms of aerodynamic force generation between fixed and flapping wings. When fixed wings translate at high angles of attack, they periodically generate and shed leading and trailing edge vortices as reflected in their fluctuating aerodynamic force traces and associated flow visualization. In contrast, wings flapping at high angles of attack generate stable leading edge vorticity, which persists throughout the duration of the stroke and enhances mean aerodynamic forces. Here, we show that aerodynamic forces can be controlled by altering the trailing edge flexibility of a flapping wing. We used a dynamically scaled mechanical model of flapping flight ( Re ≈ 2000) to measure the aerodynamic forces on flapping wings of variable flexural stiffness (EI). For low to medium angles of attack, as flexibility of the wing increases, its ability to generate aerodynamic forces decreases monotonically but its lift-to-drag ratios remain approximately constant. The instantaneous force traces reveal no major differences in the underlying modes of force generation for flexible and rigid wings, but the magnitude of force, the angle of net force vector and centre of pressure all vary systematically with wing flexibility. Even a rudimentary framework of wing veins is sufficient to restore the ability of flexible wings to generate forces at near-rigid values. Thus, the magnitude of force generation can be controlled by modulating the trailing edge flexibility and thereby controlling the magnitude of the leading edge vorticity. To characterize this, we have generated a detailed database of aerodynamic forces as a function of several variables including material properties, kinematics, aerodynamic forces and centre of pressure, which can also be used to help validate computational models of aeroelastic flapping wings. These experiments will also be useful for wing design for small robotic insects and, to a limited extent, in understanding the aerodynamics of flapping insect wings.

Interferometrically Measured Aerodynamic Forces on a Vibrating Turbine Blade Group

1980 ◽  
Vol 102 (3) ◽  
pp. 638-644
Author(s):  
Z. Kovats
Keyword(s):  
Turbine Blade ◽  
Aerodynamic Force ◽  
Low Pressure ◽  
Vibration Modes ◽  
Aerodynamic Forces ◽  
Low Pressure Turbine ◽  
Pressure Distributions ◽  
Twist Mode ◽  
Lift And Drag ◽  
Measured Pressure

The instantaneous aerodynamic force and force center during a vibration cycle were determined from interferometrically measured pressure distributions around the leading blade of a low pressure turbine blade group vibrating in the tangential, axial or twist modes. The corresponding reduced frequencies were 0.0796, 0.1088 and 0.1312, and the inlet flow Mach number was 0.59 in all tests. The energy exchange per vibration cycle between the air flow and the leading blade of a group, and the lift and drag dynamic loops were determined for each of the three vibration modes. The periodic aerodynamic force coefficients were nearly sinusoidal for the axial and torsional modes but not for the tangential mode. At large negative flow incidence, the four-blade group tested is strongly unstable in the twist mode, weakly unstable in the axial mode, and strongly stable in the tangential mode. The experimental results can be used to investigate the validity of analytical predictions of the aerodynamic forces on a vibrating low pressure blade group.

scholarly journals In vivo recording of aerodynamic force with an aerodynamic force platform: from drones to birds

2015 ◽  
Vol 12 (104) ◽  
pp. 20141283 ◽  
Author(s):  
David Lentink ◽  
Andreas F. Haselsteiner ◽  
Rivers Ingersoll
Keyword(s):  
Force Measurement ◽  
Aerodynamic Force ◽  
Force Platform ◽  
Control Surface ◽  
Flapping Wings ◽  
Free Flight ◽  
Navier Stokes Equation ◽  
Flow Measurements ◽  
Weight Support

Flapping wings enable flying animals and biomimetic robots to generate elevated aerodynamic forces. Measurements that demonstrate this capability are based on experiments with tethered robots and animals, and indirect force calculations based on measured kinematics or airflow during free flight. Remarkably, there exists no method to measure these forces directly during free flight. Such in vivo recordings in freely behaving animals are essential to better understand the precise aerodynamic function of their flapping wings, in particular during the downstroke versus upstroke. Here, we demonstrate a new aerodynamic force platform (AFP) for non-intrusive aerodynamic force measurement in freely flying animals and robots. The platform encloses the animal or object that generates fluid force with a physical control surface, which mechanically integrates the net aerodynamic force that is transferred to the earth. Using a straightforward analytical solution of the Navier–Stokes equation, we verified that the method is accurate. We subsequently validated the method with a quadcopter that is suspended in the AFP and generates unsteady thrust profiles. These independent measurements confirm that the AFP is indeed accurate. We demonstrate the effectiveness of the AFP by studying aerodynamic weight support of a freely flying bird in vivo . These measurements confirm earlier findings based on kinematics and flow measurements, which suggest that the avian downstroke, not the upstroke, is primarily responsible for body weight support during take-off and landing.

scholarly journals Birds repurpose the role of drag and lift to take off and land

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Diana D. Chin ◽  
David Lentink
Keyword(s):  
Flapping Wings ◽  
Vertical Force ◽  
Horizontal Force ◽  
Aerodynamic Forces ◽  
Braking Force ◽  
Drag And Lift ◽  
Lift And Drag ◽  
Wing Stroke

AbstractThe lift that animal wings generate to fly is typically considered a vertical force that supports weight, while drag is considered a horizontal force that opposes thrust. To determine how birds use lift and drag, here we report aerodynamic forces and kinematics of Pacific parrotlets (Forpus coelestis) during short, foraging flights. At takeoff they incline their wing stroke plane, which orients lift forward to accelerate and drag upward to support nearly half of their bodyweight. Upon landing, lift is oriented backward to contribute a quarter of the braking force, which reduces the aerodynamic power required to land. Wingbeat power requirements are dominated by downstrokes, while relatively inactive upstrokes cost almost no aerodynamic power. The parrotlets repurpose lift and drag during these flights with lift-to-drag ratios below two. Such low ratios are within range of proto-wings, showing how avian precursors may have relied on drag to take off with flapping wings.

Design and Analysis of Flapping Wing

2011 ◽  
Vol 110-116 ◽  
pp. 3495-3499
Author(s):  
G.C. Vishnu Kumar ◽  
M. Rahamath Juliyana
Keyword(s):  
Experimental Data ◽  
Flapping Wing ◽  
Micro Air Vehicle ◽  
Flapping Wings ◽  
Visualization Technique ◽  
Aerodynamic Forces ◽  
Flapping Motion ◽  
Smoke Flow ◽  
Air Vehicle ◽  
Lift And Drag

This paper the optimum wing planform for flapping motion is investigated by measuring the lift and drag characteristics. A model is designed with a fixed wing and two flapping wings attached to its trailing edge. Using wind tunnel tests are conducted to study the effect of angle of attack (smoke flow visualization technique). The test comprises of measuring the aerodynamic forces with flapping motion and without it for various flapping frequencies and results are presented. It can be possible to produce a micro air vehicle which is capable of stealthy operations for defence requirements by using these experimental data.

scholarly journals Mechanics of Forward Flight in Bumblebees: II. QUASI-STEADY LIFT AND POWER REQUIREMENTS

1990 ◽  
Vol 148 (1) ◽  
pp. 53-88 ◽  
Author(s):  
R. DUDLEY ◽  
C. P. ELLINGTON
Keyword(s):  
Steady State ◽  
Aerodynamic Force ◽  
Mechanical Power ◽  
Pitching Moment ◽  
Free Flight ◽  
Forward Flight ◽  
Hovering Flight ◽  
Aerodynamic Analysis ◽  
Drag Forces ◽  
Lift And Drag

This paper examines the aerodynamics and power requirements of forward flight in bumblebees. Measurements weremade of the steady-state lift and drag forces acting on bumblebee wings and bodies. The aerodynamic force and pitching moment balances for bumblebees previously filmed in free flight were calculated. A detailed aerodynamic analysis was used to show that quasi-steady aerodynamic mechanisms are inadequate to explain even fast forward flight. Calculations of the mechanical power requirements of forward flight show that the power required to fly is independent of airspeed over a range from hovering flight to an airspeed of 4.5 ms−1

scholarly journals Inter-species variation in number of bristles on forewings of tiny insects does not impact clap-and-fling aerodynamics

2020 ◽  
Author(s):  
Vishwa T. Kasoju ◽  
Mitchell P. Ford ◽  
Truc T. Ngo ◽  
Arvind Santhanakrishnan
Keyword(s):  
Drag Reduction ◽  
Aerodynamic Force ◽  
Physical Models ◽  
Species Variation ◽  
Aerodynamic Forces ◽  
Minimal Impact ◽  
Wing Span ◽  
Broad Variation ◽  
Geometric Variables ◽  
Lift And Drag

ABSTRACTFlight-capable miniature insects of body length (BL) < 2 mm typically possess wings with long bristles on the fringes. Though their flight is challenged by needing to overcome significant viscous resistance at chord-based Reynolds number (Rec) on the order of 10, these insects use clap-and-fling mechanism coupled with bristled wings for lift augmentation and drag reduction. However, inter-species variation in the number of bristles (n) and inter-bristle gap (G) to bristle diameter (D) ratio (G/D) and their effects on clap-and-fling aerodynamics remain unknown. Forewing image analyses of 16 species of thrips and 21 species of fairyflies showed that n and maximum wing span were both positively correlated with BL. We conducted aerodynamic force measurements and flow visualization on simplified physical models of bristled wing pairs that were prescribed to execute clap-and-fling kinematics at Rec=10 using a dynamically scaled robotic platform. 23 bristled wing pairs were tested to examine the isolated effects of changing dimensional (G, D, span) and non-dimensional (n, G/D) geometric variables on dimensionless lift and drag. Within biologically observed ranges of n and G/D, we found that: (a) increasing G provided more drag reduction than decreasing D; (b) changing n had minimal impact on lift generation; and (c) varying G/D produced minimal changes in aerodynamic forces. Taken together with the broad variation in n (32-161) across the species considered here, the lack of impact of changing n on lift generation suggests that tiny insects may experience reduced biological pressure to functionally optimize n for a given wing span.SUMMARY STATEMENTIntegrating morphological analysis of bristled wings seen in miniature insects with physical model experiments, we find that aerodynamic forces are unaffected across the broad biological variation in number of bristles.

scholarly journals How should the lift and drag forces be calculated from 2-D airfoil data for dihedral or coned wind turbine blades?

2022 ◽  
Author(s):  
Ang Li ◽  
Mac Gaunaa ◽  
Georg Raimund Pirrung ◽  
Alexander Meyer Forsting ◽  
Sergio González Horcas
Keyword(s):  
Steady State ◽  
Wind Turbine ◽  
Flow Direction ◽  
Aerodynamic Forces ◽  
Drag Forces ◽  
Thin Airfoil ◽  
Lift And Drag ◽  
Specific Implementation ◽  
Lifting Line ◽  
Blade Element

Abstract. In the present work, a consistent method for calculating the lift and drag forces from the 2-D airfoil data for the dihedral or coned horizontal-axis wind turbines when using generalized lifting-line methods is described. The generalized lifting-line methods include, for example, lifting-line (LL), actuator line (AL), blade element momentum (BEM) and blade element vortex cylinder (BEVC) methods. A consistent interpretation of classic unsteady 2-D thin airfoil theory results for use in a generally moving frame of reference within a linearly varying onset velocity field reveals that it is necessary to use not only the relative flow magnitude and direction at one point along the chord line (for instance three-quarter-chord), but also the gradient of the flow direction in the chordwise direction (or, equivalently, the flow direction at the quarter-chord) to correctly determine the magnitude and direction of the resulting 2-D aerodynamic forces and moment. However, this aspect is generally overlooked and most implementations in generalized lifting-line methods use only the flow information at one calculation point per section for simplicity. This simplification will not change the performance prediction of planar rotors, but will cause an error when applied to non-planar rotors. The present work proposes a generalized method to correct the error introduced by this simplified single-point calculation method. In this work this effect is investigated using the special case, where the wind turbine blade has only dihedral and no sweep, operating at steady-state conditions with uniform inflow applied perpendicular to the rotor plane. We investigate the impact of the effect by comparing the predictions of the steady-state performance of non-planar rotors from the consistent approach with the simplified one-point approach of the LL method. The results are verified using blade geometry resolving Reynolds-averaged Navier-Stokes (RANS) simulations. The numerical investigations confirmed that the correction derived from thin airfoil theory is needed for the calculations to correctly determine the magnitude and direction of the sectional aerodynamic forces for non-planar rotors. The aerodynamic loads of upwind and downwind coned blades that are calculated using the LL method, the BEM method, the BEVC method and the AL method are compared for the simplified and the full method. Results using the full method, including different specific implementation schemes, are shown to agree significantly better with fully-resolved RANS than the often used simplified one-point approaches.

Sign in / Sign up

Export Citation Format

Share Document