Computational and experimental investigation of aerodynamics of flapping aerofoils
Computational and experimental investigation of aerodynamics of flapping aerofoils
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.
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Computational and experimental investigation of aerodynamics of flapping aerofoils
- 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.! 30