Wind tunnel tests Progress

Wind team

Jan 2016

Wind Tunnel Testing

-provides a controlled environment where the wind turbine can be tested at different wind speeds to collect torque and rotational wind turbine speed data to produce power coefficient curves for the turbine

Cp curves for different kinds of wind turbines(Ragheb, Magdi)

Cp curves for a wind turbine at different wind speeds(Catapult Design)

Equations

• Power Coefficient: 𝐶𝑝 =𝑎𝑐𝑡𝑢𝑎𝑙 𝑝𝑜𝑤𝑒𝑟 𝑔𝑒𝑛𝑒𝑟𝑎𝑡𝑒𝑑

𝑎𝑣𝑎𝑖𝑙𝑎𝑏𝑙𝑒 𝑝𝑜𝑤𝑒𝑟 𝑓𝑟𝑜𝑚 𝑤𝑖𝑛𝑑

• Actual power generated: 𝑃𝑎 = 𝑇 ∗ 𝜔(T=Torque, 𝜔 =Rotational Speed)

• Available Power: 𝑃𝑤=1

2ρ *S*𝑉3

(ρ = air density, S = swept area, V = Wind speed)

• Swept Area: S = 2RL

(R=rotor radius, L=blade length)

• Tip Speed Ratio: TSR =𝑅𝜔

𝑉= 𝑇𝑖𝑝 𝑠𝑝𝑒𝑒𝑑 𝑜𝑓 𝑏𝑙𝑎𝑑𝑒

𝑊𝑖𝑛𝑑 𝑆𝑝𝑒𝑒𝑑

• Reynold’s #: Re = 𝜌𝑉 𝑐

ν(ν is dynamic viscosity, c is blade element chord)

Collecting Measurements• Rotational speed: can be measure with a tachometer or rotary

encoder

• Wind speed: can be measured with an anemometer or pitot tubes

• Torque: One option is to attach a DC motor to the rotor shaft to provide resistance torque loads by running the motor at a known current counter to the spin of the rotor. The torque produced by the DC motor will be equal to the torque in the rotor shaft. • If current is known and rotational speed data is collected, the following

equations can be used to calculate torque: V=IR (Ohm’s Law), P=IV, and P=T𝜔

• Start each test by turning on the wind tunnel, allowing the wind turbine to rotate freely until it reaches a steady rotational speed, and then turn on the DC motor. Collect data. The test is over once the DC motor causes the turbine to come to a complete stop.

Collecting Measurements

• Instead of the DC motor setup, torque sensors could be used to collect torque data as well.

• Set up a data acquisition system to collect data while running tests.

• Repeat tests at incremental wind speeds in a practical range of speeds

Set up of a wind turbine with a DC motor

Further Research to be done

• Blockage affect

• How to set the wind turbine up inside the wind tunnel structurally• Design Frame

• Effect of Reynold’s number

• Effect of frictional forces

• Dynamic and deep stall?

• Lift/Drag forces

Sources• 7. Design, C., Wind Turbine Test Report. 2010, San Francisco,

December.

• 5. Castillo Tudela, J., Small-Scale vertical axis wind turbine design. 2012.

• 6. Claessens, M., The design and testing of airfoils for application in small vertical axis wind turbines. Master of Science Thesis, 2006.

• 16. Ragheb, M. and A.M. Ragheb, Wind turbines theory-the betzequation and optimal rotor tip speed ratio. 2011: INTECH Open Access Publisher.

• 11. Letcher, T., Small Scale Wind Turbines Optimized for Low Wind Speeds. 2010.

Wind tunnel testing frames/test stands

Willard, N., Efficiency investigation of a helical turbine for harvesting wind energy. 2011.

Butler, V., Re-design Of The WPI Kite-powered Water Pump And Wind Turbine Systems. 2013, Worcester Polytechnic Institute.

Alé, J.A.V., et al., Performance evaluation of the

next generation of small vertical axis wind

turbine. CEP, 2007. 90619: p. 900.

Chong, W.T., et al. Design and Wind Tunnel Testing of a Savonius Wind Turbine Integrated with the Omni-Direction-Guide-Vane. in Proceedings of the Solar Conference. 2010.

Letcher, T., Small Scale Wind Turbines Optimized for Low Wind Speeds. 2010

DeCoste, J., et al., Vertical Axis

Wind Turbine. Mechanical

Engineering Dalhousie

University, 2005.

Bravo, R., S. Tullis, and S. Ziada. Performance testing of a small vertical-axis wind turbine. in Proceedings of the 21st Canadian Congress of Applied Mechanics (CANCAM07), Toronto, Canada, June. 2007.

Most similar to what we will design and use for testing:

Letcher, T., Small Scale Wind Turbines Optimized for Low Wind Speeds. 2010

Blockage Effect

• The blockage effect creates an increase in wind speed at the test section of the wind turbine, because the wind tunnel walls constrain the air

• This leads to artificially higher Cp values for a particular wind speed

• Open circuit wind tunnels are less affected by the blockage effect than closed circuit

• Blockage ratios of over 10% must be accounted for• Blockage ratio: The ratio of the wind turbine frontal area to the cross

sectional area of the wind tunnel

Blockage Corrections: Pope and Harper Method

• Blockage effect: 𝜀𝑡 = 1𝑚𝑜𝑑𝑒𝑙 𝑓𝑟𝑜𝑛𝑡𝑎𝑙 𝑎𝑟𝑒𝑎

4 𝑡𝑒𝑠𝑡 𝑠𝑒𝑐𝑡𝑖𝑜𝑛 𝑎𝑟𝑒𝑎

• Corrected wind velocity: 𝑉 = 𝑉𝑢(1 + 𝜀𝑡)• Where 𝑉𝑢 is the input wind velocity

• Use the corrected wind velocity in Cp and TSR calculations

Blockage Corrections: Corrected Maskell Method

•𝑉2

𝑉𝑢2

=1

1−𝑚(𝑆/𝐶)

• Where, S is the wind tunnel maximum frontal area, C is the cross sectional area of the test section, m = B/S, and B is the wake area normal to the wind

Wireless Strain Gauges• Used to prove that bamboo is a strong enough building material for

our wind turbine

• At least 3 strain gauges, 1 for the blade, 1 for the connector, and 1 for the center

• Information wired to the data acquisition system

• Phase IV Engineering• Said they could help

• Estimated price: $5-15 thousand

• LORD Microstrain – Williston, VT based company• Doesn’t actually sell strain gauges, only sells wireless nodes

that connect to the strain gauges

• Information from the strain gauges is sent to their base stations

• Shimmer Technology• Quoted a Strain Gauge System with 3 Strain gauges at

€1,810 ($1964.75)

• Can store data to the strain gauge units, or stream data via “BT technology to a host device”

• SENSeOR• Sells wireless strain gauges that work at different

frequencies, that can be read by a radio transceiver.

• Sent them an email for a quote – They are out of stock

• Vishay Micro Measurements• Recommended by LORD Microstrain

• Doesn’t sell wireless strain gauges

• Scanimetrics• Didn’t respond to inquiry

• Mclaren• Didn’t respond to inquiry

• Ross, I. and A. Altman, Wind tunnel blockage corrections: Review and application to Savonius vertical-axis wind turbines. Journal of Wind Engineering and Industrial Aerodynamics, 2011. 99(5): p. 523-538.

• Blackwell, B.F., R.F. Sheldahl, and L.V. Feltz, Wind tunnel performance data for two-and three-bucket Savonius rotors. 1977: Sandia Laboratories.

• Miau, J., et al., WIND-TUNNEL STUDY ON AERODYNAMIC PERFORMANCE OF SMALL VERTICAL-AXIS WIND TURBINES. In Journal of Chinese Society for Mechanical Engineers, 2012.

Blockage Ratio

• Wind tunnel cross sectional area:

3m x 3m = 118.1102 in x 118.1102 in = 13,950.02 𝑖𝑛2

• Wind turbine cross sectional area:

18 in x 27 in = 486 𝑖𝑛2

• Blockage ratio = 𝑊𝑖𝑛𝑑 𝑡𝑢𝑟𝑏𝑖𝑛𝑒 𝑐𝑟𝑜𝑠𝑠 𝑠𝑒𝑐𝑡𝑖𝑜𝑛𝑎𝑙 𝑎𝑟𝑒𝑎

𝑊𝑖𝑛𝑑 𝑡𝑢𝑛𝑛𝑒𝑙 𝑐𝑟𝑜𝑠𝑠 𝑠𝑒𝑐𝑡𝑖𝑜𝑛𝑎𝑙 𝑎𝑟𝑒𝑎=

486 𝑖𝑛2

13,950.02 𝑖𝑛2= 3.48%

• 3.48% < 5-10% so blockage effect can be neglected

Testing Frame

• To be modelled from the testing frame used in Small Scale Wind Turbines Optimized for Low Wind Speeds

• This frame matches our goals of supporting the wind turbine from above as well as below, and is also built with wood

• A magnet levitation system is used on the top support to minimize friction

• Howell, R., et al., Wind tunnel and numerical study of a small vertical axis wind turbine. Renewable energy, 2010. 35(2): p. 412-422.

• Ross, I. and A. Altman, Wind tunnel blockage corrections: Review and application to Savonius vertical-axis wind turbines. Journal of Wind Engineering and Industrial Aerodynamics, 2011. 99(5): p. 523-538.

• Chen, T. and L. Liou, Blockage corrections in wind tunnel tests of small horizontal-axis wind turbines. Experimental Thermal and Fluid Science, 2011. 35(3): p. 565-569.

• Ryi, J., et al., Blockage effect correction for a scaled wind turbine rotor by using wind tunnel test data. Renewable Energy, 2015. 79: p. 227-235.

• Letcher, T., Small Scale Wind Turbines Optimized for Low Wind Speeds. 2010.

Questions and Answers for Phase IV Engineering

• 1. How large are the blades?The wind turbine is a small vertical axis wind turbine with twistedblades, a Gorlov. The length of the airfoil of the blade is 4.5inches. The height of the rotor shaft is 21.5 inches. The bladesextend from the top to the bottom of the shaft, attached with 9 inchconnectors, which are also made out of bamboo. We would like to attacha wireless strain gauge to the connector, to the blade, and to therotor shaft. I have attached a photo of the wind turbine to the email.

2. Can we apply the strain gauges to them? (We recommend this, but we can provide the gauges, if needed)Yes

3. What is the RPM of the spinning blades?We won't know until we put the wind turbine in the wind tunnel. Wewill be testing a range of RPMs.

4. How close can you get a reader antenna to the blades?We do not know exactly. The wind tunnel we are testing in hasdimensions of 3 meters by 3 meters. The wind turbine will be placed inthe middle of the wind tunnel and just outside of the wind tunnel iswhere we will set up our equipment.

• 5. What are your target size and weight limits for the sensors? (Mostof our antenna+electronics modules are ~1.25 inches square and about0.25 to 0.5 inches thick).Those dimensions are fine.

6. Would it work better to apply the strain sensors to the blades andrun wires to the electronics+battery module that is located near theshaft?Yes

7. How often to do you want to read the strain sensors – X times per minute?The more the better. What are your suggestions?

• 8.Will it work for you if we write time-stamped strain readings to a CSVfile that can be imported into Excell?Yes, that will be great.

Used in Letcher, T. Testing

• Torque Sensor

• Rotary Encoder – used to measure rpms (alternative to using a tachometer)

• Data acquisition system

• AC induction motor• Power is applied to the motor and it resists the motion of the wind turbine,

the torque sensor measures the resistance

• Wind speed Anemometer (not needed for our experiment)

• “Labview 8.5Vishay 2120A Strain Conditioner in a Vishay 2100 Mutli-Channel Amplifier”

Used in Letcher, T. Testing

• Bellows couplings were used to correct misalignment issues between the motor and rotor shaft

• Magnetic Levitation support: Magnets are attached around the shaft an inch a half apart at the top of the test stand. The magnets are neodymium N42, (1.5" OD x 0.75" ID x 0.75" thickness)

• Torque sensor and motor attached with flex coupling

Rotary Encoder• Omron- Resolution of 100 pulses/revolution

• Used by Letcher, T. Experimeriment

• Varied diameter options (25mm, 40mm, 50mm, 55mm, 60mm)

• Sent them a request for a quote

https://www.ia.omron.com/products/category/sensors/rotary-encoders/incremental/index.html

• Letcher, T., Small Scale Wind Turbines Optimized for Low Wind Speeds. 2010.

Update on Strain Gauges: Shimmer Response

• My apologies for the delay in response.The Shimmer Strain Gauge is a wired unit allowing for strain and load cell data acquisition for force and resistance measurement, as can be seen in the attached image.http://www.shimmersensing.com/shop/bridge-amplifier

However, collected data is streamed wirelessly via Bluetooth for up to 12 meters. Each unit comes with an elastic strap, if you require a more secure option the units come in a robust plastic case, should you wish to glue the units you would be doing so at your own discretion.

• The Quotation was under $2,000, but these don’t seem to be what we’re looking for.

Final Quotation from Phase IV

• here are two options -

1) battery-free RFID strain sensors. This approach will require the least amount of custom engineering work. You would need to mount an RFID reader antenna (~8 X 8 X3 inches) about 2 feet above the shaft to read the sensors. You would be able to read them about every few seconds.Advantage: Probably a little cheaper for the engineering customization charge. I'm guessing $7,000 to $12,000 - to be determined when we have a specification. See: http://www.phaseivengr.com/solutions-demos/passive-rfid-wireless-strain-gauge/

2) battery-powered sensors. This approach will allow you to have the receiver antenna ~20 feet away and will allow you to sample at high frequency, if you wish. We have a system to do this - our ARTSS system, but it is not an "off the shelf" product yet. To customize this sensor for this application would probably be around $10,000 to $15,000. See:http://www.phaseivengr.com/artss-sensor/

• Quite Expensive

Update on Strain Gauges

• We have decided not to use wireless strain gauges, as they are very expensive and wired strain gauges can be used without having to take the wind turbine apart.

• Should we contact LORD Microstrain about using their wireless nodes and take their recommendation of using strain gauges from Vishay MicroMeasurements?

Wind Turbine

Stress/Strain

Torque

Strain Gauges

TorqueSensor

DAQ

RPMs

TachometerRotary

Encoder

Computer

Omron Incremental Encoder

Resistance Motor

Tenma Digital Tachometer

($44.99)

Tachometers

Omega Handheld Digital Tachometer ($195.00)

Design, C., Wind Turbine Test Report. 2010, San Francisco, December.

Tenma Digital Tachometer ($44.99)

Duffet, Ian, Jeff Perry, Blaine Stockwood, and Jeremy Wiseman. Design and Evaluation of Twisted Savonius Wind Turbine. (2009).

Frame Design

(Needs: Connectors for motor to torque sensor and torque sensor to wind turbine, magnets for magnetic levitation system, rotary encoder [top of shaft], strain gauges)

Wind Turbine Support

Wind Turbine Top Support: Update

• Talked to Floyd, and he recommended printing it out on the IMF printer

• However, Dr. Tan doesn’t believe the material will be strong enough

Magnetic Levitation System

• Needed:• 2 Neodymium Ring Magnets

• 3 in outer diameter, ½ in inner diameter, and ¼ in thick has about an 85 pull force

• $23.99 each from the Applied Magnets Super store

• How it works:• Two ring shaped, strong neodymium magnets are placed in close proximity to

each other, on the top rod extending from the wind turbine. Similar poles are faced towards each other, so they is a repelling force in between them. This creates a lifting force on the wind turbine, reducing the affects of friction due to gravity from the top support of the wind turbine frame during testing.

http://appliedmagnets.com/neodymium-ring-magnets-3-in-od-x-1-2-in-id-x-1-4-in-p-828.html

Magnetic Levitation System

Force

Keep Magnets from moving

(Letcher, T., Small Scale Wind Turbines Optimized for Low Wind Speeds. 2010.)

(Our frame)

Coupling to connect motor to torque sensor• CPL Flexible Shaft Couplings from Dynapar

• Options: • Model #:CPL01250375, Primary bore 3/8”,

secondary bore can be ½”, peak torque: 75 lb∙in[Price quote: $97.00]

• Model #:CPL01500375, Primary bore 3/8”, secondary can be ½”, peak torque: 100 lb∙in [Price quote: waiting to hear back]

Torque Sensor

3/8”

Motor

1/2”

https://www.dynapar.com/Products/Accessories/Specifications/CPL_Flexible_Shaft_Couplings/

Lord MicroStrain

• Recommended The V-Link LXRS, a wireless node that accepts input from up to 4 strain gauges

• We will also need a Gateway to send information from the node to the data acquisition system, WSDA-Base-101-LXRS would work.

• Both pieces of equipment would cost about $2,000.00

• Final Opinion: Too Expensive, will not be using

Omron-Rotary Encoder• Need to specify power supply voltage, output configuration, and resolution

(100 pulses per resolution was used in Letcher, T. Study) before we can get a price quote.

• Omron Distributors:• AXIS New England:

Tel:(978) 774-7100Email: axis_info_requests@axisne.com

• Airline Hydraulics CorporationTel: (866) 739-7684Email: bshiffler@airlinehyd.com

• Pearse-Bertram LLCTel: (860) 242-7777Email: adamico@pearse-bertram.com https://www.ia.omron.com/products/family/487/

Strain gauges-Which one?

http://www.vishaypg.com/micro-measurements/stress-analysis-strain-gages/