Self

Novel Blade Designs for Urban Mini-Turbines Stacey Chan & Natali Vannoy with Prof CHK Williamson

Motivation

Urban environments contain high densities of wind energy that are inaccessible to large traditional wind turbines. By exploring vertical-axis wind turbines at the small scale, we can efficiently harvest wind energy from these constrained spaces. We are developing fundamental knowledge about the fluid dynamics of the mini-turbines that has not yet been rigorously studied. The result will be a robust and radically new wind turbine that will blend engineering and art in the public setting.

Atkinson’s Center for a Sustainable Future

Straight Blades

Historically, vertical axis wind turbines have been unable to self-start. Our mini-turbines have a breakthrough design which self-start! Adding a zigzag (or sweep angle) distributes the forces along the blade to initiate rotation from rest. Our current studies show a tradeoff between self-starting and power output. When compared to straight blades, we expect to reach comparable or greater power levels by further optimizing zigzag blade design.

Counter-Rotating Turbine Pair

Broader Impact

Through-Flow mini-turbine array between walls in an alleyway

We are radically departing from classical blade designs by studying large c/D ratios, where c is the chordlength of the blade and D is the diameter of the turbine. Our tests show that larger blades extract an order of magnitude more energy than conventional smaller blades!

Furthermore, we are extracting 100x more power than vibrational energy devices!

One possibility is to integrate a prototype array on Cornell campus! A public display of renewable energy acts as a permanent outreach tool, encouraging engineering, art, and future sustainability projects.

This project is increasing the knowledge of fundamental aerodynamics of mini-turbines and will increase renewable energy in the urban environment.

Energy harvesting from small-scale vertical-axis wind turbines for the urban environment

Sibley School of Mechanical and Aerospace Engineering at Cornell University | October 2013

Cambered Blades Wind tunnel tests show that for straight blades, a symmetric airfoil shape performs the best. Increasing the camber (or curvature) of the airfoil is detrimental to power efficiency.

Sta

rt A

ngle

, θ

(deg

)

Windspeed (m/s)

120 -

100 -

80 -

60 -

40 -

20 -

0 -

3 4 5 6 7 8 3 4 5 6 7 8 3 4 5 6 7 8

Self-Starting Capacity and Max Power Output

Co-Rotating Turbine Pair

0.0

0.1

0.2

0.3

0.0 0.5 1.0 1.5 2.0

Co

effi

cien

t o

f P

ow

er

Tip Speed Ratio

Turbine Diameter: 16 cm, Pitch Angle: Optimal, Windspeed: 6 m/s

(TSR = RΩ/U)

(Cp =

P

)

0.5ρU

3 A

Micro Blades Big Blades

Power Efficiency of Different Cambered Blades Turbine Diameter: 16 cm, c/D: 0.36, Pitch Angle: optimal, Windspeed: 8 m/s

Zigzag Blades Objectives

• Increase Power Output Optimize the power output of a single turbine with a

comprehensive and previously unexplored study of the parameter space, including offset pitch angles, zigzag angle, blade camber, and relative blade sizes.

• Optimize Positive Interference

Evaluate configurations of turbine arrays for constructive interference between turbines and take advantage of the omni-directionality of the turbines.

• Artistic Concepts Encourage engineering and art in a public display

of aesthetically pleasing renewable energy harvesting systems. Potential locations include alleyways, rooftops, tunnels, under bridges, and

free-standing lattices.

Power Efficiency for Different Size Blades

Surface-Flow mini-turbine array can be placed on vertical or horizontal surfaces

The power of rapid-prototyping allows us to print 3D models quickly for testing designs in the wind tunnel at real operating conditions. We have combined techniques from 3D printing and machining to fabricate a modular testing platform. We can also use computer aided design to visualize full scale applications.

Exploded diagram of testing platform

Rapid-Prototyping

Mini-turbine in wind tunnel Ready for testing!

Zigzag blade design prior to 3D printing

Max P

ow

er (Watts)

- 4

- 3

- 2

- 1

- 0

Percent Self-Start: 15% Percent Self-Start: 95% Percent Self-Start: 54%

30o 0o 45o

Does not self-start

Maximum power curve

Does self-start

Legend

0.0

0.1

0.2

0.3

0.0 0.5 1.0 1.5 2.0

(Cp =

P

)

0.5ρU

3 A

Co

effi

cien

t o

f P

ow

er

(TSR = RΩ/U) Tip Speed Ratio

Micro Blades

c/D = 0.12

Medium Blades

c/D = 0.36

Big Blades

c/D = 0.48

Small Blades

c/D = 0.24

Legend

Legend

Large Camber

Small Camber

Symmetric

Medium Camber