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 Aerodynamic Analysis of a Flapping Wing Aircraft for Short Landing

2020 ◽  
Vol 10 (10) ◽  
pp. 3404
Author(s):  
Bing Ji ◽  
Zenggang Zhu ◽  
Shijun Guo ◽  
Si Chen ◽  
Qiaolin Zhu ◽  
...  
Keyword(s):  
Aerodynamic Characteristics ◽  
Flapping Wing ◽  
Aerodynamic Analysis ◽  
Drag Forces ◽  
Wing Model ◽  
Aerodynamic Model ◽  
Computational Fluid Dynamics Cfd ◽  
The Difference ◽  
Cfd Method ◽  
Lift And Drag

An investigation into the aerodynamic characteristics has been presented for a bio-inspired flapping wing aircraft. Firstly, a mechanism has been developed to transform the usual rotation powered by a motor to a combined flapping and pitching motion of the flapping wing. Secondly, an experimental model of the flapping wing aircraft has been built and tested to measure the motion and aerodynamic forces produced by the flapping wing. Thirdly, aerodynamic analysis is carried out based on the measured motion of the flapping wing model using an unsteady aerodynamic model (UAM) and validated by a computational fluid dynamics (CFD) method. The difference of the average lift force between the UAM and CFD method is 1.3%, and the difference between the UAM and experimental results is 18%. In addition, a parametric study is carried out by employing the UAM method to analyze the effect of variations of the pitching angle on the aerodynamic lift and drag forces. According to the study, the pitching amplitude for maximum lift is in the range of 60°~70° as the flight velocity decreases from 5 m/s to 1 m/s during landing.

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.

Dragonfly flight. I. Gliding flight and steady-state aerodynamic forces.

1997 ◽  
Vol 200 (3) ◽  
pp. 543-556 ◽  
Author(s):  
JM Wakeling ◽  
CP Ellington
Keyword(s):  
Steady State ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
The Body ◽  
Flat Plates ◽  
Viscous Forces ◽  
Drag Forces ◽  
Aerodynamic Properties ◽  
Gliding Flight ◽  
Lift And Drag

The free gliding flight of the dragonfly Sympetrum sanguineum was filmed in a large flight enclosure. Reconstruction of the glide paths showed the flights to involve accelerations. Where the acceleration could be considered constant, the lift and drag forces acting on the dragonfly were calculated. The maximum lift coefficient (CL) recorded from these glides was 0.93; however, this is not necessarily the maximum possible from the wings. Lift and drag forces were additionally measured from isolated wings and bodies of S. sanguineum and the damselfly Calopteryx splendens in a steady air flow at Reynolds numbers of 700-2400 for the wings and 2500-15 000 for the bodies. The maximum lift coefficients (CL,max) were 1.07 for S. sanguineum and 1.15 for C. splendens, which are greater than those recorded for all other insects except the locust. The drag coefficient at zero angle of attack ranged between 0.07 and 0.14, being little more than the Blassius value predicted for flat plates. Dragonfly wings thus show exceptional steady-state aerodynamic properties in comparison with the wings of other insects. A resolved-flow model was tested on the body drag data. The parasite drag is significantly affected by viscous forces normal to the longitudinal body axis. The linear dependence of drag on velocity must thus be included in models to predict the parasite drag on dragonflies at non-zero body angles.

scholarly journals The Kinematics and Aerodynamics of the Free Flight of some Diptera

1989 ◽  
Vol 142 (1) ◽  
pp. 49-85 ◽  
Author(s):  
A. ROLAND ENNOS
Keyword(s):  
High Speed ◽  
Aerodynamic Force ◽  
Linear Equations ◽  
Free Flight ◽  
Forward Flight ◽  
Flight Behaviour ◽  
Representative Species ◽  
High Speed Cinematography ◽  
Novel Method ◽  
Third Dimension

Seven representative species of the order Diptera were filmed in free flight using high-speed cinematography. Insects were killed after filming, and morphological measurements were made in the manner of Ellington (1984b). The detailed kinematics of selected sequences were then found using frame-by-frame digitization, followed by computer reconstruction of the third dimension. Kinematics were qualitatively similar to those observed by Ellington (1984c), though in three species the wings often underwent ventral flexion near the base at the end of the downstroke. For aerodynamic analysis of hovering flight, modified forms of the equations of Ellington (1984e,f) were used. Forward flight was analysed by a novel method, which assumes that an equal but opposite circulation is built up for each half-stroke and allows linear equations to be used. The lift coefficients calculated for hovering were commonly well above those possible by quasi-steady mechanisms, but rotational coefficients were within those that could be achieved by the unsteady lift mechanisms: clap-and-fling (Weis-Fogh, 1973) and flex (Ellington, 1984d). The lift and rotational coefficients of the two half-strokes were often unequal. In forward flight, the equal circulation assumption often led to an incorrect estimation of the aerodynamic force vector, showing that the circulations during the two half-strokes were unequal. It is suggested that flies manoeuvre largely by altering the unsteady circulations produced at stroke reversal via alterations in the speed and timing of wing rotation. The differences in the mechanisms used by different fly species are related to their flight behaviour in the field.

Transient Simulation Method for Autorotation in Forward Flight

2013 ◽  
Vol 284-287 ◽  
pp. 1001-1006 ◽  
Author(s):  
Hak Yoon Kim
Keyword(s):  
Steady State ◽  
High Speed ◽  
Equations Of Motion ◽  
Simulation Method ◽  
Transient Simulation ◽  
Rotor Speed ◽  
Forward Flight ◽  
Data Set ◽  
Shaft Angle ◽  
Lift And Drag

This paper describes the Transient Simulation Method (TSM) which predicts the steady state and performance of autorotation in forward flight. Flapping and rotational equations of motion are integrated from an arbitrary initial rotor speed, and the steady state of autorotation is obtained as a periodic solution through a transient process. The induced velocity field update method and the average thrust, lift, and drag computations during the transition are described in detail. TSM is then applied to the model rotor to validate the feasibility. High speed autorotation is simulated using an aerodynamic data set that is analyzed by the two-dimensional compressible Navier-Stokes Solver. Rotor speed variation for increases in airspeed at low shaft angle is presented and discussed. When TSM is used with sophisticated aerodynamic data analyzed as functions of the blade angle of attack, the Reynolds number, and the Mach number, the autorotation range for the collective pitch, velocity, and shaft angle can be reasonably explored.

Aerodynamics of hovering flight in the long-eared bat Plecotus auritus

1976 ◽  
Vol 65 (2) ◽  
pp. 459-470 ◽  
Author(s):  
U. M. Norberg
Keyword(s):  
Steady State ◽  
Drag Coefficient ◽  
Lift Coefficient ◽  
Quasi Steady State ◽  
Hovering Flight ◽  
Drag Coefficients ◽  
Lift And Drag

Steady-state aerodynamic and momentum theories were used for calculations of the lift and drag coefficients of Plecotus auritus in hovering flight. The lift coefficient obtained varies between 3-1 and 6-4, and the drag coefficient between --5-0 and 10-5, for the possible assumptions regarding the effective angles of attack during the upstroke. This demonstrates that hovering flight in Plecotus auritus can not be explained by quasi-steady-state aerodynamics. Thus, non-steady-state aerodynamics must prevail.

Aerodynamics, kinematics, and energetics of horizontal flapping flight in the long-eared bat Plecotus auritus

1976 ◽  
Vol 65 (1) ◽  
pp. 179-212 ◽  
Author(s):  
U. M. Norberg
Keyword(s):  
Steady State ◽  
Power Output ◽  
Lift Coefficient ◽  
Mechanical Efficiency ◽  
Flapping Flight ◽  
Mechanical Power ◽  
Power Stroke ◽  
Force Coefficient ◽  
Mechanical Power Output ◽  
Lift And Drag

The kinematics, aerodynamics, and energetics of Plecotus auritus in slow horizontal flight, 2–35 m s-1, are analysed. At this speed the inclination of the stroke path is ca. 58 degrees to the horizontal, the stroke angle ca. 91 degrees, and the stroke frequency ca. 11-9 Hz. A method, based on steady-state aerodynamic and momenthum theories, is derived to calculate the lift and drag coefficients as averaged over the whole wing the whole wing-stroke for horizontal flapping flight. This is a further development of Pennycuick's (1968) and Weis-Fogh's (1972) expressions for calculating the lift coefficient. The lift coefficient obtained varies between 1-4 and 1-6, the drag coefficient between 0-4 and 1-2, and the lift:drag ratio between 1-2 and 4-0. The corresponding, calculated, total specific mechanical power output of the wing muscles varies between 27-0 and 40-4 W kg-1 body mass. A maximum estimate of mechanical efficiency is 0–26. The aerodynamic efficiency varies between 0–07 and 0–10. The force coefficient, total mechanical power output, and mechanical and aerodynamic efficiencies are all plausible, demonstrating that the slow flapping flight of Plecotus is thus explicable by steady-state aerodynamics. The downstroke is the power stroke for the vertical upward forces and the upstroke for the horizontal forward forces.

scholarly journals Measurements of Unsteady Periodic Forces generated by the Blowfly Flying in a Wind Tunnel

1981 ◽  
Vol 90 (1) ◽  
pp. 163-173
Author(s):  
RICHARD H. BUCKHOLZ
Keyword(s):  
Wind Tunnel ◽  
Vertical Force ◽  
Free Flight ◽  
Wind Speeds ◽  
Sarcophaga Bullata ◽  
Drag Forces ◽  
Harmonic Content ◽  
The Mean ◽  
Lift And Drag ◽  
Force Accuracy

A technique was developed for the measurement of the instantaneous lift and drag forces generated by the blowfly, Sarcophaga bullata, flying fixed in a wind tunnel. Apparatus for the measurement of insect-generated forces was checked in part for mean force accuracy by measurement of the drag on a circular cylinder. Our experimental device detects the sum of the aerodynamic forces and wing inertial forces as experienced by the thorax. The streamwise and vertical force waveforms show a surprising lack of higher harmonic content. Wind speeds in the neighbourhood of the known preferred flying speed were used, without an explicit attempt to nullify the mean vertical and horizontal forces to simulate free flight. Several measurements of the phase angle between the force waveform and the wing beating kinematics indicated that vertical forces in the liftward direction achieved a maximum during the downstroke and thrustward forces achieved a maximum during the upstroke.

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.

scholarly journals Preliminary Results on the Dynamics of a Pile-Moored Fish Cage with Elastic Net in Currents and Waves

2020 ◽  
Vol 9 (1) ◽  
pp. 14
Author(s):  
Gianluca Zitti ◽  
Nico Novelli ◽  
Maurizio Brocchini
Keyword(s):  
Numerical Model ◽  
Laboratory Experiments ◽  
Numerical Models ◽  
Offshore Structures ◽  
Fish Farm ◽  
Maximum Displacement ◽  
Drag Forces ◽  
Real Size ◽  
Lift And Drag ◽  
Mesh Grid

Over the last decades, the aquaculture sector increased significantly and constantly, moving fish-farm plants further from the coast, and exposing them to increasingly high forces due to currents and waves. The performances of cages in currents and waves have been widely studied in literature, by means of laboratory experiments and numerical models, but virtually all the research is focused on the global performances of the system, i.e., on the maximum displacement, the volume reduction or the mooring tension. In this work we propose a numerical model, derived from the net-truss model of Kristiansen and Faltinsen (2012), to study the dynamics of fish farm cages in current and waves. In this model the net is modeled with straight trusses connecting nodes, where the mass of the net is concentrated at the nodes. The deformation of the net is evaluated solving the equation of motion of the nodes, subjected to gravity, buoyancy, lift, and drag forces. With respect to the original model, the elasticity of the net is included. In this work the real size of the net is used for the computation mesh grid, this allowing the numerical model to reproduce the exact dynamics of the cage. The numerical model is used to simulate a cage with fixed rings, based on the concept of mooring the cage to the foundation of no longer functioning offshore structures. The deformations of the system subjected to currents and waves are studied.

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