Design of a Compact Test-Stand for a Small-Scale Wind Turbine Blade

Student Team: Antonio Gomez, Chris Harrell, Michael Taylor, Anthony Valdez

Faculty: Prof. Cristina Davis, Prof. Valeria La Saponara

Design Criteria

Motivation Material Selection and Costs

Calculations

Testing and Results

Conclusions and Future Work

Acknowledgements

Computer Aided Design & Manufacturing

CAD software was used to model each component of the

stand in order to assist the manufacturing process. Finite Element

Analysis was performed to simulate the stand in loading

conditions.

All sheet metal flanges and mounting plates were cut

by a CNC Plasma Cutter in order to rapidly produce identical parts.

Other Operations

Square tubing and flanges were joined by MIG welding

while the blade and mounting plates were joined using

½ in. Grade 5 bolts.

Structural members were powder coated to prevent

corrosion and increase the stands longevity.

Manufacturing

System Architecture

𝑈𝑠𝑖𝑛𝑔 𝑀 = 12000 𝑙𝑏 − 𝑖𝑛 𝑎𝑛𝑑 𝐿 = 18𝑖𝑛 𝛿𝑚𝑎𝑥 =𝑀𝐿2

2𝐸𝐼= 0.0735 𝑖𝑛𝑐ℎ𝑒𝑠

Deflection Analysis

In order to ensure accurate deflection data, the metal stand

must not flex or bend during testing. Therefore, the section

experiencing the highest bending moment was evaluated.

Weld Analysis

This moment is resisted by the welds at the base of the stand. The nominal throat

shear stress was calculated in order to confirm that the weld would stand.

𝑈𝑠𝑖𝑛𝑔 𝑀 = 12000 𝑙𝑏 − 𝑖𝑛, 𝑐 = 1.414, 𝑎𝑛𝑑 𝜏′′ =𝑀𝑐

𝐼 𝐹𝑎𝑙𝑙𝑜𝑤 = 5.303

𝑘𝑖𝑝

𝑙𝑖𝑛. 𝑖𝑛𝑐ℎ while 𝐹𝑎𝑐𝑡𝑢𝑎𝑙 = 4.242

𝑘𝑖𝑝

𝑙𝑖𝑛. 𝑖𝑛𝑐ℎ

The stand was designed to have a slot modular design. This was done so that upgrading

different sections could be done easily without affecting the other functional fragments. The

figures below display the individual functional assemblies as well as how they all come

together to perform their intended function.

Our team would like to thank the National Science Foundation for its grant

CMMI-1200521 to Dr. Ken Loh (CEE) and Dr. Valeria La Saponara (MAE), that

sponsored our project. We would also like to thank Dr. Cristina Davis and Mr.

Frederick Meyers for helping us with our design throughout the entire process.

We would also like to acknowledge all the College of Engineering faculty and

staff, especially the EFL staff, for making the execution of this project possible.

Thank you.

Will be replaced with FEA

CNC Plasma Cutter

The stand was fabricated from A500 steel structural 2 inch

square tubing which was chosen for it’s durability, ease of

machining and welding, and it’s strength. We decided to use

analog components for our electronics because we wanted real

time data acquisition on our sensors as well as low cost. We

were awarded a generous budget from NSF; of which we only

used a fraction, with the majority being spent on electronics that

can be used in future projects.

A low-cost, easily deployable structural health monitoring (SHM) method is

desired for wind turbine blades, to reduce off time, operation and

maintenance costs, safety risks, and make this technology more attractive to

utility companies. Since MAE researchers operate a 1 kW wind turbine on

the roof of Bainer Hall, field-testing on this turbine was going to be possible

after preliminary testing of a SHM method in the laboratory, on blades or

spars of the wind turbines.

Previously, to test wind turbine blades the

ACRES lab would stack weights on top of the

blade and measure deflections with a ruler.

This method was limited to static tests only

and the deflection and load measurements

were not very accurate.

When designing the test stand, we researched current methods of

loading wind turbine blades. The picture above demonstrates one of the

current methods used by the National Renewable Energy

Laboratory (NREL) for static testing. Using this as a guide, we decided to

use a linear stepper motor so we could test static and dynamic loading.

Testing and Results Sensor Calibration

The load cell was calibrated by measuring the change in output voltage

when a load column applied various loads to it.

The string potentiometer was calibrated by measuring the change in output

voltage as it was being extended to prescribed lengths.

Stepper Motor Testing

The stepper motor was tested to be sure it could

apply enough force during the static test to

break the wind turbine blade. The test revealed

that the stepper motor stalled at 311 newtons,

but was able to apply 300 newtons without

stalling, which is 50% more force than the

estimated 200 newtons it will take to break the

spar of a re-engineered wind turbine blade. The

picture on the right shows the motor being

loaded with approximately 220 newtons.

Data Acquisition During Dynamic Loading of the Blade

Stock Material

5% Hardware

1%

Electronics

27% Unused

67%

Budget Analysis by Category

If given more time to improve the

test stand, the following features

would be added:

• A longer lead screw for increased

travel

• Another protoboard for more

permanent wiring

• Larger non-captive stepper motor

which would increase the

possible dynamic test frequency

and quasi-static load limit.

The test stand was successfully

built with the required

specifications:

• Applies over 150% of the

required minimum load

• Runs dynamic loading with a

frequency of 0.3 Hz

• Efficiently records testing

data using myDAQ, ARDUINO,

and LabVIEW

• Was built for only 33% of the

allowed cost.

Stand Requirements

• Compact size due to limited space in ACRES Lab

• Must remain rigid during testing

• Easily portable by a single person

Load Application

• Ability to impart a 200 newton flapwise static load on a 1m long blade

• Dynamic loading with a frequency close to 0.5 Hz

• Apply load at a rate of 7 newtons per second for quasi-static testing

Data Acquisition

• Measure and record the load during the test and at the time of failure

• Measure and record the displacement of the blade or spar during the

test and at the time of failure