Design and Evaluation of a Twisted Savonius Wind Turbine Ian Duffett Jeff Perry Blaine Stockwood Jeremy Wiseman
Outline Problem Definition Introduction Concept Selection Design Fabrication Testing Results Conclusions Recommendations
Problem Definition Design and test a vertical axis wind turbine (VAWT). This design should meet the following objectives: Design will be novel and untested Design will be self-starting Design will produce reliable power in harsh weather conditions
Wind Energy The conversion of wind energy into various other useful forms such as electricity is known as wind power Studying wind energy is desirable because: Wind energy is renewable There is ample supply of wind energy Suitable wind patterns are available worldwide Production costs of wind energy are declining Wind energy produces minimal greenhouse gas emissions
Wind Turbines Horizontal Axis Wind Turbines (HAWT) Advantages Higher efficiency Can furl out of the wind to reduce wind speed seen by the blades High towers reduce turbulence caused by nearby structures Disadvantages Tower mounting makes maintenance more difficult Requires large structures Installation requires heavy equipment Requires additional controls to furl and rotate to orient blades in the wind direction Vertical Axis Wind Turbines (VAWT) Advantages Ground mounting makes maintenance easier Can be installed in areas of wind funnelling and high wind speeds Lower noise signature Requires lower starting speeds Disadvantages Lower efficiency May require guys to support rotation axis Can create an inconsistent torque (pulse)
Major Types of VAWT 1. Darrieus Wind Turbine Uses lift to create rotation Good efficiency Torque ripple Not self-starting 2. Savonius Wind Turbine Uses drag forces to create rotation Low efficiency High reliability Self-starting A very large Darrieus wind turbine on the Gaspé peninsula, Quebec, Canada Savonius wind turbine
Twisted Savonius Increases efficiency of standard savonius wind turbine Consistent torque created by symmetrical helical shape Rotates regardless of wind direction Self-starting
Concept Selection Modified Twisted Savonius Turbine Provides consistent torque Will be self-starting Will only rotate at the wind speed allowing for greater reliability in high wind Design is untested Closed around shaft
Prototype Modelling Bottom Plane Independent Design Parameters: Long Radius α Short Radius Angle of Twist Short Radius Bottom Plane r Short Radius R r Long Radius Bottom Plane α R Top Plane Long Radius Top Plane 360 180 360 180
CFD Analysis FloWorks simulation developed to test static torque on various foil designs: Constant velocity air stream, 15m/s Measure torque generated on shaft
CFD Analysis 0.5 0.6 Elliptical Circular Foil Design Circular Foil Design Torque (N m) 0.5 0.4 0.4 0.3 0.3 Maximum Torque @ 360 Twist Angle 0.47 N m 0.2 Elliptical Foil Design 0.2 Maximum Torque @ 360 Twist Angle, 108.3 mm Long Radius 0.1 0.1 0 0.56 N m Torque (N m) Torque (N m) 0.5 0 1 0.5 0 Circular Foil Design 0 90 180 270 360 450 540 630 720 Angle of Twist ( ) Elliptical Foil Design 0 50 100 150 Long Radius (mm) 0 90 20 180 40 270 60 360 80 450 100 540 120 630 140 720 160 Long Angle Radius of Twist (mm)) ( )
Prototype Fabrication Rapid Prototyping Fused Deposition Modeling Turns computer-aided design (CAD) geometry into solid state structures. Max Build Size 10 x 10 Sectioned Prototype Required Build time ~ 36 hours per section Two Section Shaft $6300
Prototype Fabrication Design Plan
Prototype Fabrication Prototyping Challenges Prototyper Size Constraints Problem: Limitations in nozzle movement prevented achieving maximum cross-section Solution: 5% Reduction in CAD Model Size Problem: Damage to nozzle heads due to overheating of material in the semi-liquid state Solution: Reduced size (by height) of individual foil sections to decrease run time and prevent overheating
Prototype Fabrication Prototyping Challenges Assembly Problem: Shrinkage of the material during cooling from the semiliquid state Solution: Use of body filler during assemblage to create continuous foil surface Problem: Rotational unbalance within the foil due to body filler and flexibility of shaft Solution: Replacement of two shaft aluminum design with single steel shaft
Wind Tunnel Setup Memorial University s Wind Tunnel - Wind Speed Range 1.2 m/s (Full Closed) to 10.6 m/s (Fully Open) - Rectangular test section 20.0 x 0.93 x 1.04 meters
Wind Tunnel Setup Setup 1 Installed centered and vertically in the wind tunnel with both ends of the shaft extruding through the bottom and top of the tunnel (2 x Alum 1/2 OD x 36, inserted at both ends) Low friction polyblock bearings Setup 1 Problems Large vibrations during rotation of Blade Not installed: Friction Brake Dynamometer Anemometer LED Tac
Wind Tunnel Setup Setup 2 Installed centered and vertically within the wind tunnel with a shorter shaft (Steel 7/16 OD x 36 ) Low friction shaft bearings Instrumentation setup: LED Tac / Handheld Tac Friction Brake Dynamometer Anemometer Setup 2 Problems Vibration of Friction Brake Dynamometer Pulse loading on load cell LED Tac sampling rate limited to 50 Hz Unable to capture flywheel rotations fast enough
Setup 2 - Pictures
Wind Tunnel Setup Setup 3 Installed centered and vertically within the wind tunnel with a shorter shaft (Steel 7/16 OD x 36 ) Low friction shaft bearings Instrumentation setup: Handheld Tac Friction Brake Dynamometer Anemometer Setup 3 Problems Vibration of Friction Brake Dynamometer Pulse loading on load cell
Setup 3 - Pictures
Testing Matrix - Number of Tests -> 36
Testing Predictions Predicted Results Two important design features are: Tip Speed Ratio (TSR or λ) Is the ratio between the rotational speed of the tip of a blade and the actual velocity of the wind Power Coefficient (Cp) The power coefficient tells how efficiently a turbine converts wind energy into electricity
CFD / Testing Comparison FloWorks simulations were developed over a range of wind speed for static torque and compared to static test acquired throughout testing
Testing Results 0.160 Cp vs. Tip Speed 14.000 Power Output vs. Wind Speed 0.140 12.000 0.120 10.000 Cp 0.100 0.080 0.060 Power Output [Watts] 8.000 6.000 0.040 4.000 0.020 2.000 0.000 0.000 0.200 0.400 0.600 0.800 1.000 0.000 0.0 2.0 4.0 6.0 8.0 10.0 12.0 TSR Wind Speed [m/s]
Summary Successful test of novel design Design determined to be self starting under varying wind conditions Maximum 15% efficiency achieved Maximum Power Output of 13 Watts Cp vs. TSR Plot follows a similar profile of the predicted Power and torque output increases as wind speed increases
Plan Forward & Next Steps Improve testing set-up for more reliable results Use high frequency DAQ to accurately measure rotation speed Review friction brake design to measure more consistent loads Test under Newfoundland environmental conditions Icing and snow tests Higher wind speeds Longer term effect of sea spray and fog on system performance
Special Thanks to: Dr. Iqbal Steve Steel Matt Curtis Craig Mitchell Don Taylor
This Concludes our Presentation Questions? Thank you for your Attention http://www.engr.mun.ca/~blaines/