Numerical Prediction of Aerodynamic Characteristics of a Hummingbird

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ISSN : 2319 – 3182, Volume-2, Issue-3, 2013

13

Numerical Prediction of Aerodynamic Characteristics of a Hummingbird

Vishnupriya . R, Sharpunisha. N, Raju Govindharajan & G. Chandra Bose Dept. of Aeronautical Engineering P. B. College of Engineering,

E-mail : [email protected], [email protected], [email protected] & [email protected]

Abstract – Hummingbirds are widely thought to employ aerodynamic mechanisms similar to aircrafts. Also hummingbird wings are capable of operating in more viscous regimes. The present analysis is to study the aerodynamics of a hummingbird using computational simulation. The wake patterns around the bird is simulated which significantly enables to visualize the pressure distribution and flow patterns. The lift and drag forces were measured from which high values of lift: drag ratio at low angles of attack is obtained. The above result concludes that wings of hummingbird are good at producing more lift.

Keywords – aerodynamics, angle of attack, lift coefficient, drag coefficient.

I. INTRODUCTION

Hummingbirds have been studied for their unusual display of aerodynamics. It weighs one-fourteenth of an ounce and, like helicopters, can fly forward, backward, sideways and can hover in mid-air. They are among the smallest of birds, most species measuring in the 7.5–

13 cm (3–5 inch) range. This bird‟s wings appear to be backwards (i.e.) the leading edge of its wing is behind the feathers. This is because of the wing movement horizontally back and forth during hovering. The Reynolds number for a hummingbird hover flight ranges from 10³to 10⁴and flapping frequency is about 41 Hz (i.e.) they can hover in mid-air by rapidly flapping their wings 12–80 times per second. And also they are capable of greater forward velocities, exceeding 30 ms^-1.

Hummingbird flight has been studied intensively from an aerodynamic perspective. There are many forces of interest, from the tilt of the body to the stroke of the wings. Everything combines together to form an inspiring hummingbird flight. They have higher angle of attack at mid down stroke than during mid upstroke. In both halves of the wing stroke, the feathers point downward at an angle to produce lift. Earlier studies had

assumed that lift was generated equally during the phases of the wing beat cycle. When hummingbird aerodynamics employs the use of down stroke to hover, about a quarter of their weight is supported by it and the upstroke supports the rest. Such extensive research performed on determining the mechanism involved in hummingbird aerodynamics and hence it has the power to influence the technology employed in future flying machines. In fact, the mechanisms of helicopters have been influenced by the study of hummingbird aerodynamics.

Zongxian Liang et al ^[3]numerically simulated the hummingbird wings model undergoing hovering flight.

3D wake structures and its associated aerodynamic performance were visualised. It was found that the amount of lift produced during down stroke is about 3 times of that produced in upstroke and also two parallel vortex rings were formed at the end of the upstrokes.

Douglas L. Altshuler et al ^[3] compared the aerodynamic forces of revolving hummingbird wings and wing models. The lift an drag forces were measured and it was observed that the lift: drag ratios of real wings were substantially higher than those of wing models.

Bret W. Tobalske et al ^[4] studied the aerodynamics of hummingbird flight using Digital Particle Image Velocimetry. DPIV analysis suggested that an extended wing upstroke during forward flight produces lift and negative thrust and circulation during down stroke is sufficient to support body weight.

Donald R. Powers et al ^[3] determined that the airflow over hummingbird wings is dominated by a stable, attached leading edge vortex. Using PIV technique the 2D flow field around the wing of a hummingbird is captured from which the vorticity over the dorsal surface is visualised. And hence the lift

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International Journal on Theoretical and Applied Research in Mechanical Engineering (IJTARME)

14 production decreases until the energy of the leading edge vortices is re-captured.

II. METHODOLOGY A. Physical Model

The 3D cad model used for computational analysis is modelled using CATIA and the same is shown in figure 1. On comparing the various data‟s of a hummingbird, the length and wing span is taken as 48 mm and 28 mm respectively.

Fig. 1 : Hummingbird Model B. Numerical Approach

The computational grid used for this analysis is shown in figure 2(a). The surface mesh with required mesh refinements is created with the total surface elements of 134754. An unstructured volume mesh is created with a growth rate of 1.2. The numerical analysis is carried out using RANS based CFD solver.

For the present analysis 3D incompressible equations are solved with air as the working fluid. The standard k- ε model is activated in order to capture the turbulent flow properties over the bird.

Fig. 2(a) : Refined Volume Mesh Around The Bird

Fig. 2(b) : Computational Domain C. Boundary conditions

The flow at the inlet domain is set to subsonic with the following solver setup

The exit of the domain is set to „pressure outlet‟

boundary condition. The entire bird model is set to „no- slip wall‟ boundary condition with standard wall functions

III. RESULTS AND DISCUSSION

Numerical simulation of external flow field around the bird is predicted. The analysis is carried out for various angles of attack and its corresponding static pressure distribution, wake patterns and turbulence intensities are captured and the same is shown in figure 3(a).

Fig. 3(a) : Static Pressure Distribution Around The Bird FLOW (time) STEADY

FLOW (density) INCOMPRESSIBLE

EQUATIONS

CONTINUITY,

MOMENTUM AND K- EPSILON

MATERIAL TYPE

LUID(ATMOSPHERIC AIR)

FLOW

INITIALIZATION 11.11 m/s REFERENCE

PRESSURE 1 atm

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15 The above figure displays the static pressure rise at the ventral portion of the body as a result of abrupt reduction in flow velocity.

The figure 3(b) displays the static pressure distribution over the wings for 4 degree angle of attack .The maximum pressure at the ventral side and low pressure at the dorsal portion are captured. This significantly increases the lift.

Fig. 3(b) : Static Pressure Distribution over the wings for 4 degree angle of attack

Figure 3(c) displays the static pressure distribution over the cross section of the wing profile at 4 degree angle of attack, for which maximum lift is obtained. Maximum pressure is generated at leading edge of the cross section.

Fig. 3(c) : Static Pressure Distribution Across The Wing Profile

The aerodynamic forces are calculated from which the lift to drag ratio is obtained. The maximum lift and stall angle of the bird is determined from the plots shown in figure 3(d) and 3(e). The results are discussed below.

Fig. 3(d) : CL VS. Alpha Curve

Fig. 3(e): CD VS. Alpha Curve

From the above plots it is concluded that the maximum lift is generated for 4 degree angle of attack and the drag increases gradually. Further, when the angle of attack is increased, stall occurs.

IV. CONCLUSION

The 3D numerical simulation of aerodynamic characteristics of a hummingbird is carried out . The flow physics around the bird is predicted from which it is observed that high values of lift is obtained at low angle of attack. The trend of drag vs. Angle of attack curve shows increment in drag as angle of attack increases. This is because the projected area of the bird increases as the flow angle increases. Thus the computational methodology very well predicts the flow physics of a hummingbird.

REFERENCES

[1] Zongxian Liang¹ and Haibo

Dong²”COMPUTATIONAL ANALYSIS OF

HVERING HUMMINGBIRD FLIGHT

“Department of Mechanical & Materials Engineering, Wright State University, Dayton.

[2] Douglas R. Warrick¹,*, Bret W. Tobalske² and Donald R. Powers ³ “ LIFT PRODUCTION IN HOVERING HUMMINGBIRD FLIGHT “ Department of Zoology, Oregon State University, 3029 Cordley Hall, Corvallis, OR 97331, USA2Field Research Station at Fort Missoula, Division of Biological Sciences, University of Montana, Missoula, 3Biology Department, George Fox University, 414 N. Meridian Street, Newberg, , USA.

[3] Douglas R. Warrick ¹and Bret W. Tobalske²

“THE AERODYNAMICS OFHUMMINGBIRD 0.3

0.32 0.34 0.36 0.38 0.4

-4 -3 -2 -1 0 1 2 3 4 5 6 CL

α (degree)

0.2 0.22 0.24 0.26 0.28 0.3 0.32

-5 0 5 10

CD

α ( degree )

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16 FLIGHT “Oregon State University, Corvallis Oregon 97331 and University of Portland, Portland

[4] Douglas L. Altshuler', Robert Dudley ²and Charles P. Ellington ³ “AERODYNAMIC FORCES OF REVOLVING HUMMINGBIRD WINGS “ University of Texas at Austin, Austin, Texas, U.S.A. Smithsonian Tropical Research Institute, Balboa, Republic of Panama

NOMENCLATURE

CL Force coefficient in y direction CD Force coefficient in x direction α Angle of attack (degree) Re Reynolds number

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