Renewal interest on the exploitation of flapping flight motions to attain high propulsion efficiency of air vehicles is inspired by the aerodynamics of birds’ and insects’ flights. The flapping characteristics can be majorly used to develop micro aerial vehicles (MAV) as this is a lucrative method to generate lift and thrust simultaneously. In this project, the variation of the flow properties and the thrust generation of an airfoil in a flapping (plunging) motion, is evaluated using both computational and experimental methods. The NACA 2412 airfoil was selected for the study and, the computational method was carried out using an inviscid flow model and computational fluid dynamics (CFD) simulations, simultaneously to obtain and compare the variation of properties. The inviscid model was developed using conformal mapping and potential flow theories, and it is capable of producing results for any arbitrary aerofoil. Steady-state results were compared and validated in both CFD and inviscid flow modelling as the computational framework along with flow visualisation and force sensing as the experimental framework. The validated CFD and inviscid models have been developed to produce a plunging motion to the aerofoil and obtain the variation of drag and lift coefficients with time. The experimental setup was designed to obtain the forces acting on the airfoil, and the flow characteristics were visually observed using a flow visualization technique. The force calculations were done through a developed and optimized load cell arrangement. The developed smoke flow visualisation technique is capable of successfully capturing streamline patterns, flow separation regions. These results were compared along with wake development between computational and experimental models. The Level of agreement and limitations of each method have been discussed in this report.

1. Computational and Experimental
Investigation of
Aerodynamics of Flapping Airfoils
Group members
K.M.G.L. Dilshan
D.H.S. Abenayake
W.M.K.S. Weerasekara
M.L.L.U. Gunaratne
1

2. 2
Real bird Simplified model
Flapping Motion

3. 3
Aim
• To develop a computational and experimental framework to
investigate the aerodynamic characteristics of flapping airfoils
Objectives
• To develop a computational framework to capture flapping wing
motion and flow characteristics
• To design and develop an experimental setup with a data acquisition
system to obtain flow properties
• Analyze how the propulsion effect can be improved with varying
flapping characteristics

4. 4
Computational Framework
• Inviscid flow model
• Viscous flow model
Experimental Framework
• Flow visualisation setup
• Force calculation setup
Project
methodology

5. 5
Validation of the viscous model
Experimental ClXFOIL ClANSYS Cl
ANSYS Cd XFOIL Cd

6. 6
• K-ω Shear Stress Transfer RANS model was chosen
Validation of the viscous model

7. 7
Validation of the viscous model
Experimental Cl
Simulated Cl
Cp Experimental Cp
Simulated
• Number of elements was varied from 15,000 to 980,000

8. 8
Final Mesh
Final Mesh
• Average skewness 0.21
• Average orthogonal quality
0.925
• Number of Elements 484,000
Mesh input parameters
• Angle of attack
• Distance from the front
of the airfoil
• Distance from the back of
the airfoil

9. Velocity field variation in plunging at 5Hz Velocity field variation in pitching at 4Hz
Vorticity field in plunging at 5Hz
User Defined Function parameters
• Plunging frequency
• Plunging amplitude
A combined motion of pitching and
plunging was also developed

10. 10
5Hz Plunging comparison of Cl of 0.05s and 0.02s step sizes
• Considering the simulation time and the gained improvement, along with the range of
variation , the step size of 0.005s was finalized
Time Convergence

11. 11
Inviscid Model Development

12. 12
Inviscid Model Development
Vortex emerging point selection Complete inviscid model

13. 13
Inviscid Model - Validation

14. 14
Inviscid Model - Validation

15. 15
Inviscid Model – Plunging motion
(Frequency: 1Hz, Amplitude: 0.25m, AoA: 0°)

16. 16
Load Cell Design and Manufacturing For Wind Tunnel Testing
• Drag force 0 – 2 N
• Lift force 0 – 4N
• Crosstalk - less than 1%
• Strain required > 10^(-4)

17. 17
Final Design
Lift
Drag
Load Cell
Structur
e
Force Direction Strain X direction Strain Y direction
Lift 3.658 x 10-4 7.172 x 10-7
Drag 1.6719 x 10-6 1.6231 x 10-4
Force Direction Crosstalk X Crosstalk Y
Lift - 0.19%
Drag 0.97% -

18. 18
Manufacturing and Testing

19. 19
Smoke Flow Visualization Setup – Smoke Generating Machine
Liquid
reservoir
Pump
Thermostat
cut off – 2700C
Glass woolAluminium
metal block
Copper tube
Heating element
Nozzle

20. 20
Smoke Flow Visualization Setup – Smoke Rake

21. 21
Smoke Flow Visualization Setup – Steady State Results
progress

22. 22
Plunging Motion – Scotch Yoke Mechanism

23. 23
Plunging Motion – Results

24. Comparison – Steady-state – Streamline Pattern
0°
10°
15°
Inviscid model CFD model Flow visualization

25. 25
Comparison of lift
coefficient variation
with angle of attack
Comparison – Steady-state – Coefficient of Lift (Cl)

26. Comparison – Plunging – Coefficient of Lift (Cl) & Coefficient of Drag (Cd)

27. Comparison – Plunging – Trailing Edge Vortex Shedding (Wake Pattern)
CFD Model
Inviscid Model
Experimental Model

28. Limitations
Inviscid Model CFD Model Flow Visualization
Only for low Strouhal number region
for plunging
Time consuming – 8hrs Streamlines are not clear in higher
Reynolds numbers
Need to be improved for pitching - Plunging mechanism have limitations
on maximum amplitude and
maximum frequency
Cannot identify flow separation -

29. Limitations – Experimental load cell apparatus
Effect of moment on lift measurement Effect of moment on drag measurement

30. Thank You.!
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