This document summarizes the design and testing of a compact test stand for small-scale wind turbine blades. Key points: - CAD software was used to model components and FEA was performed to simulate loading conditions. Sheet metal and tubing were cut with a CNC plasma cutter and welded together. - Deflection analysis showed the stand would flex less than 0.0735 inches under maximum load. Weld analysis confirmed welds could withstand stresses. - A stepper motor was tested and could apply over 50% more force than needed to break a blade. Load cells and string potentiometers were calibrated to measure and record loads and displacements. - Testing showed the stand met requirements

1. 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 𝛿 𝑚𝑎𝑥 =
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