Ryan McGowan and Narayanan Komerath
Daniel Guggenheim School of Aerospace Engineering
Georgia Institute of Technology
Atlanta, Georgia USA
INTERNATIONAL CONFERENCE ON POWER, SIGNALS, CONTROL AND COMPUTATIONS
Trissur, India, January 3-06, 2012
Georgia Institute of Technology komerath@gatech.edu
Experimental Aerodynamics & Concepts Group
Micro Renewable Energy Systems Laboratory
Validation of a Prediction
Model for Control of Micro
Wind Turbines
SUMMARY
•Develop micro wind turbine for
single-family use in India
•Vertical axis vs. horizontal axis
•Local manufacture & maintenance
•Lifecycle safety & environment
•Technically complex to design!
Objective
Optimize design for low tip-speed ratio
TSR = Blade tip tangential\ Windspeed
•Operation at low wind speeds
•Low blade tip speed
TSR
Methods
•Aerodynamics simulation validated
•Low Reynolds number corrections
•Wind tunnel testbed
•Azimuthal modification strategy to
improve operation
•Real-time control options
Georgia Institute of Technology komerath@gatech.edu
Experimental Aerodynamics & Concepts Group
Micro Renewable Energy Systems Laboratory
Aim
1. Bicycle-based 1m VAWT >270rpm,
>70 w (mechanical)
2. 2m 1kW VAWT for high coastal winds.
Issues:
1. Optimal tip speed ratio 2 to 5 – too high.
2. Variable power transmission
3. Nonlinear pitch control
4. Flexible blade operation
5. Benign failure modes
6. Hybrid devices: power conditioning,
storage
Georgia Institute of Technology komerath@gatech.edu
Experimental Aerodynamics & Concepts Group
Micro Renewable Energy Systems Laboratory
Vertical Axis Wind Turbine
Georgia Institute of Technology komerath@gatech.edu
Experimental Aerodynamics & Concepts Group
Micro Renewable Energy Systems Laboratory
54-inch Horizontal Axis Wind Turbine
Electrical Output vs. Wind Speed, with 50 Ohm resistive
load (2 tests)
Micro Renewable Energy Systems Laboratory
Experimental Aerodynamics & Concepts Group
Horizontal Axis Wind Turbine Simulation:
Power Coefficient vs. Tip Speed Ratio
Georgia Institute of Technology komerath@gatech.edu
40
30
20
10
10
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30
40
Georgia Institute of Technology komerath@gatech.edu
Experimental Aerodynamics & Concepts Group
Micro Renewable Energy Systems Laboratory
Measured VAWT mechanical power in two tests vs.
preliminary predictions from momentum streamtube
theory.
Vt = - Vb
Solidity, defined as diameter divided by blade chord times number of
blades.
As solidity increases, blade-wake interaction increases.
So we need Multiple StreamTube Theory to account for power loss from
streamtubes due to power extraction or drag due to blades
Georgia Institute of Technology komerath@gatech.edu
Experimental Aerodynamics & Concepts Group
Micro Renewable Energy Systems Laboratory
Vertical Axis Wind Turbine, looking from above, showing relative velocity
on the Advancing Blade Side, and the blade wake.
Blade element
predictions of the
mechanical power output
of the 3-armed, bi-bladed
VAWT, for different
choices of blade chord
compared to the baseline
chord, with fixed span
Baseline AR =
Span/chord. ~9
Georgia Institute of Technology komerath@gatech.edu
Experimental Aerodynamics & Concepts Group
Micro Renewable Energy Systems Laboratory
Aspect Ratio Effect on Optimal Tip Speed Ratio
Georgia Institute of Technology komerath@gatech.edu
Experimental Aerodynamics & Concepts Group
Micro Renewable Energy Systems Laboratory
Power coefficient vs. tip speed ratio for various solidities
(Sandia data and simulation)
Georgia Institute of Technology komerath@gatech.edu
Experimental Aerodynamics & Concepts Group
Micro Renewable Energy Systems Laboratory
Comparison of (GT) and Sandia performance
predictions at a solidity of 0.18.
Micro Renewable Energy Systems Laboratory
Experimental Aerodynamics & Concepts Group
Positive Torque (driving) occurs when net force has a positive
component along the tangential direction, driving the blade
Tangential coefficient vs. alpha for a NACA 0015 airfoil
Georgia Institute of Technology komerath@gatech.edu
Passive Starting Mechanisms
•Enable startup in low winds
•Provide some power
•Limit performance at high
•speeds
Wind
Guide Vanes
• Passive control of local angle
of attack
• Eliminate blade stall/negative torque
• Allow self-starting
To reach optimal TSR, one needs powered start
Georgia Institute of Technology komerath@gatech.edu
Experimental Aerodynamics & Concepts Group
Micro Renewable Energy Systems Laboratory
Drag Channels
Begun to integrate prediction, design and testing of a 2m x 2m vertical axis
wind turbine with slanted double blades.
Operating point predictions with multiple streamtube theory are validated
against published results. Reynolds number effects are clearly seen in the
predictions, and their proper inclusion allows the predictions to match
experimental data well.
Low performance at Tip Speed Ratio <1 is as per predictions. Simulation used
to study how to eliminate negative torque at low tip speed ratio.
A self-starting device using drag tubes isbeing simulated.
Limiting turbine speed for safety implies that high tip speed ratio is best
achieved at low wind speeds by taking the turbine to operating speed using
human pedaling action or an electric motor.
Time-resolved simulations and thus to control algorithms for adapting to given
wind patterns and optimizing power extraction and safety.
Georgia Institute of Technology komerath@gatech.edu
Experimental Aerodynamics & Concepts Group
Micro Renewable Energy Systems Laboratory
Conclusions
The work reported in this paper was made possible by resources being
developed for the “EXTROVERT” cross-disciplinary learning project
under NASA Grant NNX09AF67G S01. Mr. Anthony Springer is the
Technical Monitor.
Georgia Institute of Technology komerath@gatech.edu
Experimental Aerodynamics & Concepts Group
Micro Renewable Energy Systems Laboratory
ACKNOWLEDGEMENTS