THE AERODYNAMICS OF BIRD FLIGHT
Ekam Sra
Raheem Akinosho
Xue Bai
Backgroud Introduction
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Humans have studied the bird
flight for a long time.
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Bird flight is a very high energy
cost activity.
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This physiology of bird flight is
used in aeroplanes also.
Figure from Aerodynamics of bird flight, Rudolf Dvoák
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Bird Wings
It has●
●
●
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Primaries
Secondaries
Alula
Coverts
Regardless of having different wings, the mechanism of the bird flight is the same.
There are mainly 2 types of movement of the bird wing
1.Flapping mode
2.Oscillating mode
Figure from Aerodynamics of bird flight, Rudolf Dvoák
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Bernoulli’s Principle
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Bernoulli’s principle says that Velocity is inversely proportion to Pressure.
V = 1/P
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Now when air passes through the wing, It bifurcates.
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The upper curve is convex side and the bottom curve is concave.
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The concave side has less surface area resulting low velocity. Convex has more
surface area therefore, high velocity.
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Upper side- Low P, High V
Lower side- High P, Low V
Tip vortices- Turbulence created around the wings, helps in the lift.
Figure from Terakita's Air/Aerodynamics & Flight, Mary Kay Carson
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Objective
To understand or determine the bird flight movement and different hypotheses
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used to explain its aerodynamics.
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·
To create a quasi-steady model using fluent to perform a numerical solution of
the flapping wings and its aerodynamics performance..
Forces that act on the wing
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Lift Force- Perpendicular component of aerodynamic force to the flow direction.
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Drag Force- Drag is a force acting opposite to the relative motion.
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Theory of Aerodynamic Forces
•An aerodynamic force is a force placed on a body by the air in which it is submerged, and
is due to the relative motion between the body and the gas.
There are two components of the resulting aerodynamic force acting on the wing;
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•Lift is defined as the perpendicular component of aerodynamic force to
the flow direction.
• Drag is an aerodynamics force that opposses relative motion with
respect to a surrounding fluid.
• Bird wings provide lift to allow them to fly, which is often thought of
as a vertical force that supports weight.
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Aerodynamics Performance of an Airfoil
The two main component of an airfoil aerodynamics performance
are;
❏
❏
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Aerodynamics of Gliding Flight
Us = Usinθ ---------------------- (i)
L = mgcosθ ---------------------- (ii)
D = mgsinθ ---------------------- (iii)
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Components of Flying Bird Drag
➢ Parasite drag: This occurs as the bird's body is propelled through the air.
Dpar =
-------------------- (iv)
➢ Profile drag: This is produced as the wings move through the air.
Dpro =
----------------- (v)
➢ Induced drag: This is due to the downwash produced by the bird's wing
and tail when producing lift.
Dind =
----------------- (vi)
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Coefficients of The Lift and Drag of the Gliding Bird Flight
● Lift Coefficient
-------------------- (vii)
● Drag Coefficient
-------------------- (vii)
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Pitching Moment
Angle of Attack
This is the nose up or down direction of
the bird movement usually during take
off and landing.
● This is the angle between the
wing and the direction of the
upcoming wind.
● Lift pitches forward to accelerate
the bird and counter drag during
takeoff.
● Lift pitches backward to augment
braking forces generated by drag.
● The bird lift increase as the
angle of attack increases.
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Vortex
A vortex is a rotating column of air
generated by the bird wing during
positive or negative aerodynamic lift.
The vortex, containing high
velocity airflows, increases the
lift produced by the wing.
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Numerical Model: Flapping Foil
Parameters
Variables
Air velocity
3m/s
Time step size
0.2 s
Total time
1.0 s
NACA4412
-5
Air dynamic viscosity
1.789410 kg/ms
Air density
1.225 kg/m3
Reynolds number
50296
3m
6m
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Numerical Model: Flapping Foil
Pitch-pivot-point
Rotation, θ(t)
Vertical motion, h(t)
By User Defined Function:
Plunge motion: h(t)=hmcos(2ft)=hmcos(2t/tp);
Pitch motion: θ(t)=θmsin(2ft)=θmsin(2t/tp);
The location of pitch–pivot-point: xp=c/4.
hm: amplitude of pluging motion (m);
θm: amplitdue of pitching motion (o);
f: flapping frequency (Hz);
tp: time period (s).
Figure from David Sibley. IDENTIFYING SMALL SONGBIRDS BY FLIGHT STYLE. Sibley Guides. March 11, 2011
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Lift and Drag Coefficient
❖
Lift Coefficient (CL)
Peak value at θ = 0o
❖
Drag Coefficient (CD)
Peak value at θ = +40o or -40o
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Dynamic Vorticity Contour
Counterclockwise
vortex
Clockwise
vortex
Vorticity far wake
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Vorticity and Pressure Contour
Single vortex
Pressure distribution symmetic about the horizaontal axis
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Turbulence Kinetic Energy and Velocity Contour
❖
Turbulence kinetic energy
❖
Velocity
Impact downward momentum
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Conclusion
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Aerodynamics theory provided a theoretical framework for the
understanding of bird flight.
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References
1.
Iosilevskii, G. (2014). Forward flight of birds revisited. Part 1: aerodynamics and performance. Royal Society Open Science, 1(2), 140248.
2.
Platzer, M. F., Jones, K. D., Young, J., & Lai, J. C. S. (2008). Flapping Wing Aerodynamics: Progress and Challenges. AIAA Journal, 46(9), 2136–2149.
3.
Dvořák, R. (2016). Aerodynamics of bird flight. EPJ Web of Conferences, 114, 01001.
4.
Carruthers, A. C., Walker, S. M., Thomas, A. L. R., & Taylor, G. K. (2010). Aerodynamics of aerofoil sections measured on a free-flying bird. Proceedings of the
Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering, 224(8), 855–864.
5.
Tang, D., Fan, Z., Lei, M., Lv, B., Yu, L., & Cui, H. (2019). A combined airfoil with secondary feather inspired by the golden eagle and its influences on the
aerodynamics. Chinese Physics B, 28(3), 034702.
6.
Heathcote, S., & Gursul, I. (2007). Flexible Flapping Airfoil Propulsion at Low Reynolds Numbers. AIAA Journal, 45(5), 1066–1079.
7.
Veldman, A. (2005). Quasi-Simultaneous Viscous-Inviscid Interaction for Transonic Airfoil Flow (invited). 4th AIAA Theoretical Fluid Mechanics Meeting.
8.
Aldheeb, M. A., Asrar, W., Sulaeman, E., & Omar, A. A. (2016). A Review on Aerodynamics of Non-Flapping Bird Wings. Journal of Aerospace Technology and
Management, 8(1), 7–17.
9.
Yang, S., Liu, C., & Wu, J. (2017). Effect of motion trajectory on the aerodynamic performance of a flapping airfoil. Journal of Fluids and Structures, 75,
213–232.
10.
Cheng, B., Roll, J., Liu, Y., Troolin, D. R., & Deng, X. (2014). Three-dimensional vortex wake structure of flapping wings in hovering flight. Journal of The
Royal Society Interface, 11(91), 20130984.
11.
Klein Heerenbrink, M., Johansson, L. C., & Hedenström, A. (2015). Power of the wingbeat: modelling the effects of flapping wings in vertebrate flight.
2022 April 6th
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