1. Maple Seed Performance as a Wind Turbine
Jacob Holden, Thomas Caley, Mark Turner
University of Cincinnati
SciTech 2015, 1/5/2015 – 1/9/2015
Gaylord Palms Hotel & Convention Center, Kissimmee, Florida
- Explain the Single- Bladed Wind Turbine….what are we looking at?

2. Key Findings Betz’ limit for turbine and maple seed performance
Power Coefficient Cp,max = ; Cp,seed = 0.59
Axial induction factor amax = 1/3; aseed = .313
Thrust Coefficient CT,max= 0.89; CT,seed= 0.86
This genetically evolved seed geometry is closer to the optimal coefficient of power than any existing wind turbine design
Has time reached a truly optimal design?
Context each of the parameters
Mention “optimal”…introduce it, then emphasize It later…pose question
Transition by saying I will talk about:
Motivation
Mechanics of autorotation
Momentum theory (Betz Limit)
Method

3. Why the Maple Seed?
Biomimicry – “an approach to innovation that seeks sustainable solutions to human challenges by emulating nature’s time-tested patterns and strategies.” [5]
The maple seed performs the task of a wind turbine, harnessing the kinetic energy of a moving fluid to generate lift.
[6]

4. Objectives
Simulate the natural aerodynamics of a mapleseed with 3D Computational Fluid Dynamics.
Analyze the performance of the maple seed as a wind turbine using present wind turbine performance parameters.

5. MAPLE SEED FLIGHT MECHANICS

6. Autorotation (1) Vf = final relative air speed
Vs = initial relative air speed (sinking speed)
Vertical velocity components from Norberg [2].

7. Autorotation (2)
Resultant velocity vector incident on maple seed LE in autorotation from Norberg [2].

8. PERFORMANCE ANALYSIS

9. 1D Momentum Theory and Betz Limit
Used to explain the maple seed in autorotation.
Define an axial induction factor
Bernoulli’s function gives expression for axial force, a power coefficient can then be determined.
[7]
Bernoulli’s equation gives expression for power….Normalized by power in wind to get Cp
dCp/da =0 gives a_max=1/3

10. Axial Induction Factor vs. Cp
Betz’ theory invalid
What happens at a = 0.5
a_max=
Cp_max=

11. ROTATION PARAMETERS AND GEOMETRY

12. High Speed Video - Autorotation
16°
3000 frames per second
Still images used to estimate coning angle
4 seeds dropped (3 trials each), values averaged
ω = 824 RPM (σ = 9.03%)
VS = m/s (σ =6.10%)
Note that this high speed is not Acer Negundo
Video chosen for its quality for presentation purposes

13. 3D Geometry Generation 3D solid part model generated.
3D Model
CFD Domain
3D solid part model generated.
CT Scans by Exact Metrology [1].
Cylindrical duct extruded around seed for solver domain.

14. Rotation Summary Coning angle = 16° VS = 0.739 m/s
Tip Speed Ratio, TSR = (low end of wind turbine range)
The Center of Rotation (determined from high speed video) is of particular interest as well.
Talk about C.M. and what that means
2 LE
Area Variation in radial direction
Should have a dimension to seed tip

15. CFD SIMULATION

16. CFD Simulation (1) Star-CCM+ package chosen (CAD, gridding, solver).
Inlet velocity (vertical seed velocity), vd= m/s imposed.
Reference frame for rotation imposed with average ω= 824 rpm.
Results will focus on rotation reference frame

17. CFD Simulation (2) Mesh Solver Unstructured Prism Layer
Surface Remesher
Tetrahedral Mesher
820,649 total cells
Reynolds-Averaged Navier-Stokes
Three-dimensional
Incompressible flow
Coupled flow
k-ε turbulence model
Steady flow
Two layer y+ treatment
Initial turbulence intensity of 1%
Justify why RANS and why k-epsilon
Cite paper ******

18. RESULTS

19. Static Pressure Distribution
Static pressure contours on pressure and suction sides from CFD
Static pressure distribution leading edge to trailing edge from Norberg [2].

20. Relative Velocity Stream Tubes

21. Leading Edge Vortex Seed profile
Relative tangential velocity isosurface Vtan = m/s
Relative velocity stream tubes
V_tan isosurface is an indicator of separation (not necessarily a bad thing if flow reattaches
Surface around rotational axis EXPLAIN THIS HOW?
Seed Profile
LE bulge will absolutely cause a separated region after, verified by Vtan isosurface
V_rel streamlines twist in a region of separated flow
Low momentum particles are influenced more by rotational motion…hence the radial flows at the LE (separation and low v)

22. Stream Tube Boundaries
Flow Direction
Rotation Axis
Rotation Axis

23. Power Calculation
Surface integral of axial velocity (U2) as plane just upstream of seed.
a = (94% of max)
CP = 0.59 (99.6% of max)
amax = 0.333
CP,max = U1 U2

24. Force Balance Net axial force on seed = 4.932 x 10-4 N
Weight of an Acer Negundo seed sample = x 10-4 N
36% difference in axial force (thrust) and weight balance, attributed primarily to the significant variation in different samples of the same species.
For avertical =0, Faxial= Wseed

25. Reverse Engineering
Airfoil section created from cross-sectional analysis of 3D CT scans.
Maple seed blade generated using in house 3DBGB code [8].
Spanwise variation of chord and stagger angle.
- Mention that most recent results suggest that the seed body plays a key role in the performance, so future work will include reverse engineering the entire seed (embryo + leaf)
Airfoil section
3D Blade Geometry

26. Other Applications
The seed’s ability to efficiently dissipate energy suggest it would serve well as a decelerator.
Cheap, reliable, and effective deployment potential
Air drop to remote locations
Reusable 1st stage rockets
UAV’s dropped at altitude for one mission
MAV applications by MIT and Lockheed Martin
[9]

27. Conclusion
Interesting, novel, fun, and relatable aerodynamics problem.
The maple seed behaves as a wind turbine and operates nearer to theoretical CP and axial induction factor maximums than other turbine geometries.
Other techniques such as LES may be necessary for further investigation. Present method was appropriate for investigating potential.

28. Future Work
LES to better characterize flow behavior, especially around the embryo (seed base).
Explore the influence of embryo and the cross-sectional area variation in the spanwise direction [4].
Use seed geometry as initial solution for and 3D blade optimization.
Finite element stress analysis.

29. References Exact Metrology, http://www.exactmetrology.com/
Norberg, R. A. (1973). “Autorotation, Self-Stability, and Structure of Single-Winged Fruits and Seeds (Samaras) With Comparative Remarks on Animal Flight.” Biol. Rev, 48, 561–596.
Manwell, J. F., McGowan, J. G., and Rogers, A. L., Wind energy explained : Theory, design and application. Wind Energy. John Wiley and Sons, Inc., 1st edition, 111 River Street,Hoboken, NJ
Sairam, K., “The Influence of Radial Area Variation on Wind Turbines to the Axial Induction Factor”. Master’s thesis University of Cincinnati.
"What is Biomimicry?" The Biomimicry Institute, Missoula, Montana. [ biomimicry/. Accessed 11/17/14.]
D. Lentink, W. B. Dickson, J. L. van Leeuwen, and M. H. Dickinson, Leading-Edge Vortices Elevate Lift of Autorotating Plant Seeds, Science 324, (2009)
Ingram, G., October Wind turbine blade analysis using the blade element momentum method version 1.1, Durham University.
Siddappaji, K., “Parametric 3d blade geometry modeling tool for turbomachinery systems”. Master’s thesis University of Cincinnati.,