experiment b11/b12 turbine design procedureprumbach/ame20217/b11/f19_b11_b12_procedure.pdf ·...

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University of Notre Dame Aerospace and Mechanical Engineering AME 21217: Lab II Fall 2019 B11/12 – Turbine Design 1 Last Revision: 11/15/19 Experiment B11/B12 Turbine Design Procedure Deliverables: Checked lab notebook, Full Lab Report (due the day of the contest) Overview A turbine is a device that extracts kinetic energy from a moving fluid. We will spend the remainder of the semester designing and building turbines. Your turbines will be tested in a commercially built system known as the Wind Trainer. The Wind Trainer is a small wind tunnel containing a dynamometer, which is used to simultaneously measure torque τ and angular velocity ω of the spinning turbine. Multiplying torque τ (in units of N m) and angular velocity ω (in units of rad/s) yields shaft power P shaft = τω (in units of Watts). Similar to B5 - Build-a-Beam, this final project will take the form of a contest to determine who can design and build the turbine that extracts the most power P shaft . Unlike the B5 - Build-a-Beam contest, you will have a virtually unlimited amount of material to work with and 3 weeks to design, test, and redesign your turbine. Really, the only constraints in this project are time and the physical dimensions of the Wind Trainer. Safety Rules 1. Safety glasses must be worn when operating the Wind Trainer or any power tools. 2. The Wind Trainer must be powered down when mounting the turbine to the dynamometer. 3. The inlet side of the Wind Trainer must be sealed off by the red grate before the fan can be turned on. 4. Do NOT walk or stand by the inlet or outlet of the Wind Trainer while the fan is running. 5. Sharp objects such as Exacto knife and box cutter blades must be properly disposed in an appropriate sharps container. 6. The TA or Lab Instructor must be present to supervise operation of the Wind Trainer. 7. The TAs and Lab Instructors reserve the right to veto any design they deem to be unsafe. Wind Trainer and Dynamometer The Wind Trainer system has a variable speed fan, a pitot probe for measuring the airspeed, and a dynamometer for measuring the torque and angular velocity of the turbine. Angular velocity ω is measured by an optical tachometer coupled to the dynamometer shaft, and the dynamometer measures torque τ via a friction belt connected to a load cell. Adjusting the tension in the dynamometer’s friction belt changes the torque on the turbine. As the torque τ is increased, the angular velocity ω will decrease. For a turbine, an engine, or a motor, the relationship between torque and angular speed is known as a torque curve. (This is similar to a hydraulic pump curve.) A sample torque curve for a wind turbine is shown via the left-hand axis of Figure 1. For large

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Page 1: Experiment B11/B12 Turbine Design Procedureprumbach/AME20217/B11/F19_B11_B12_procedure.pdf · Experiment B11/B12 Turbine Design Procedure Deliverables: Checked lab notebook, Full

University of Notre Dame Aerospace and Mechanical Engineering AME 21217: Lab II Fall 2019

B11/12 – Turbine Design 1 Last Revision: 11/15/19

Experiment B11/B12 Turbine Design

Procedure

Deliverables: Checked lab notebook, Full Lab Report (due the day of the contest) Overview A turbine is a device that extracts kinetic energy from a moving fluid. We will spend the remainder of the semester designing and building turbines. Your turbines will be tested in a commercially built system known as the Wind Trainer. The Wind Trainer is a small wind tunnel containing a dynamometer, which is used to simultaneously measure torque τ and angular velocity ω of the spinning turbine. Multiplying torque τ (in units of N m) and angular velocity ω (in units of rad/s) yields shaft power Pshaft = τω (in units of Watts).

Similar to B5 - Build-a-Beam, this final project will take the form of a contest to determine who can design and build the turbine that extracts the most power Pshaft. Unlike the B5 - Build-a-Beam contest, you will have a virtually unlimited amount of material to work with and 3 weeks to design, test, and redesign your turbine. Really, the only constraints in this project are time and the physical dimensions of the Wind Trainer.

Safety Rules 1. Safety glasses must be worn when operating the Wind Trainer or any power tools.

2. The Wind Trainer must be powered down when mounting the turbine to the dynamometer. 3. The inlet side of the Wind Trainer must be sealed off by the red grate before the fan can be

turned on. 4. Do NOT walk or stand by the inlet or outlet of the Wind Trainer while the fan is running.

5. Sharp objects such as Exacto knife and box cutter blades must be properly disposed in an appropriate sharps container.

6. The TA or Lab Instructor must be present to supervise operation of the Wind Trainer. 7. The TAs and Lab Instructors reserve the right to veto any design they deem to be unsafe.

Wind Trainer and Dynamometer The Wind Trainer system has a variable speed fan, a pitot probe for measuring the airspeed, and a dynamometer for measuring the torque and angular velocity of the turbine. Angular velocity ω is measured by an optical tachometer coupled to the dynamometer shaft, and the dynamometer measures torque τ via a friction belt connected to a load cell. Adjusting the tension in the dynamometer’s friction belt changes the torque on the turbine. As the torque τ is increased, the angular velocity ω will decrease. For a turbine, an engine, or a motor, the relationship between torque and angular speed is known as a torque curve. (This is similar to a hydraulic pump curve.) A sample torque curve for a wind turbine is shown via the left-hand axis of Figure 1. For large

Page 2: Experiment B11/B12 Turbine Design Procedureprumbach/AME20217/B11/F19_B11_B12_procedure.pdf · Experiment B11/B12 Turbine Design Procedure Deliverables: Checked lab notebook, Full

University of Notre Dame Aerospace and Mechanical Engineering AME 21217: Lab II Fall 2019

B11/12 – Turbine Design 2 Last Revision: 11/15/19

torque, note that the angular speed is zero, because applying a large torque causes the turbine to stall.

Multiplying the torque and angular velocity yield the shaft power

Pshaft =ωτ , (1) which is the power that can be extracted from the moving fluid by the turbine. The shaft power is not constant, but rather it depends on the angular speed and torque. The relationship between shaft power and angular velocity is known as the power curve. (This is similar to the hydraulic pump’s efficiency curve.) A sample power curve is shown via the right-hand axis Figure 2. Note that there is an optimal angular velocity and torque that yields the most power. It will be up to you to determine the optimal operating parameters τ and ω for your blade design. At the time of the contest, you will adjust the dynamometer to provide these optimal parameters.

Figure 1 – A torque curve (left axis) shows the torque, while a power curve (right axis) shows the total shaft power as a function of angular speed in RPM.

A few more important points for operating the Wind Trainer:

• When using the tool for setting the pitch angle, place the hub on the shaft such the set screws are facing the main post in the middle.

• When mounting the hub in the Wind Trainer, orient the hub such that the set screws are facing the inlet.

• Make sure the set screw in the center of the hub is tightened onto the flat part of the shaft.

900 1000 1100 1200 1300 1400 1500angular velocity, (RPM)

0

0.02

0.04

0.06

0.08

0.1

0.12

torq

ue,

(Nm

)

0

2

4

6

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10

shaf

t pow

er, P

shaf

t (W)

Page 3: Experiment B11/B12 Turbine Design Procedureprumbach/AME20217/B11/F19_B11_B12_procedure.pdf · Experiment B11/B12 Turbine Design Procedure Deliverables: Checked lab notebook, Full

University of Notre Dame Aerospace and Mechanical Engineering AME 21217: Lab II Fall 2019

B11/12 – Turbine Design 3 Last Revision: 11/15/19

Contest Rules 1. Each lab section will be divided into teams of two or three.

2. The winner of the contest will be the group whose turbine can produce the most power Pshaft = τω at an airspeed of u = 12.0 ± 0.3 m/s, which will be measured and set by the lab instructor without any turbine mounted to the shaft.

3. The torque τ and angular velocity ω will be determined using the instrumentation built into the Wind Trainer.

4. At the time of the contest, students must adjust the belt tension to yield what they have determined to be the optimal torque and angular speed for their blades. The product of this optimal torque τ and angular velocity ω will be used to calculate the shaft power Pshaft = τω.

5. The major constraint for this project is experimental test time. Each team will be given only two 20 minute long time slots to test their various prototypes. (A Google spreadsheet will be shared with the class to facilitate this.)

6. It is the students’ responsibility to make the best use of their allotted test time. We will not allow students to make-up test time that was lost due to their own ill preparedness.

7. Turbine designs must be original, and all CAD drawings must be produced from scratch. If you wish to 3D print your design, you must base your CAD drawing off of a standard 2D NACA airfoil. In your report, you must explicitly state the NACA 4 digit airfoil specification.

8. Downloading and printing designs from websites like thingiverse.com will be considered plagiarism and will be referred to the Dean’s office as a violation of the academic honor code.

9. Turbines must fit within the Wind Trainer work space. The blades must not scrape the walls. The blades must not touch the Pitot probe nor any part of the dynamometer system.

10. It is the responsibility of the students to measure all dimensions of the Wind Trainer and design their turbine accordingly.

11. All fabricated turbine components must be physically coupled to the shaft of the dynamometer. That is, your design cannot include any extraneous parts to redirect flow through the Wind Trainer.

12. You may not modify the Wind Trainer in any way. 13. Turbines must be radially symmetric with a center of mass located on the shaft.

14. Turbines may be constructed out of balsa wood and dowels or be 3D printed. If you wish to use any other material, you must first ask the instructor for approval.

15. Students must begin by constructing a “crude” prototype made of wood. We will provide the following materials for this:

• 6” long, 3/16” diameter wooden dowels • 1/8” thick, 36” long strips of balsa wood with various widths • Hot glue sticks

Page 4: Experiment B11/B12 Turbine Design Procedureprumbach/AME20217/B11/F19_B11_B12_procedure.pdf · Experiment B11/B12 Turbine Design Procedure Deliverables: Checked lab notebook, Full

University of Notre Dame Aerospace and Mechanical Engineering AME 21217: Lab II Fall 2019

B11/12 – Turbine Design 4 Last Revision: 11/15/19

16. Pre-made aluminum hubs are available with 12 equally spaced 3/16” holes for mounting

blades and a center hole for mounting the entire assembly to the dynamometer shaft. These hubs are for everyone’s shared use and must remain in B14 Fitzpatrick.

17. Students may also design and fabricate their own center hub for mounting their blades, but it must be securely coupled to the dynamometer shaft in a manner that will not damage the dynamometer shaft. Please consult the lab instructor for approval if you decide to go this route.

18. Tools will be available in 212 Stinson-Remick. You are required to clean up your workspace and return all tools to the appropriate locker when you are finished.

19. If a blade breaks off or becomes dislodged from the hub during testing, it will result in a one-point deduction from the performance score. Students must rearrange the remaining blades into a radially symmetric pattern and continue testing without replacing the broken blades.

20. If the top performers are within 5% of each other, it will be considered a tie, and a special runoff contest will be held at a variety of different airspeeds to see who can produce the highest average power.

21. Professor Ott and Professor Rumbach will act as arbitrators in any dispute or controversial outcome that may arise and have the right to declare shenanigans at any point in time. And for the support of a fair contest,with a firm reliance on the protection of divine providence, we mutually pledge our Lives, our Fortunes, and our sacred Honor.

Performance Grade 5% of your overall grade in this course will be determined by how well your turbine performs. Essentially, a grade out of 5 points will be assigned based on the shaft power produced by your turbine.

a. Students more than one standard above the mean will receive a 5/5. b. Students within one standard deviation above the mean will receive a 4/5.

c. Students within one standard deviation below the mean will receive a 3/5. d. Students more than one standard deviation below the mean will receive a 2/5.

e. Students more than two standard deviations below the mean will receive a 1/5. f. Students more than three standard deviations below the mean will receive a 0/5.

g. If a blade breaks off or becomes dislodged during testing, the group will receive an automatic 1-point deduction from their performance grade. The students must then repeat the test with the remaining undamaged blades that did not become detached from the hub.

Page 5: Experiment B11/B12 Turbine Design Procedureprumbach/AME20217/B11/F19_B11_B12_procedure.pdf · Experiment B11/B12 Turbine Design Procedure Deliverables: Checked lab notebook, Full

University of Notre Dame Aerospace and Mechanical Engineering AME 21217: Lab II Fall 2019

B11/12 – Turbine Design 5 Last Revision: 11/15/19

Final Lab Report Using the proper format specified on the course website (see the LaTeX template or MS Word example), write a full lab report, no longer than 7 pages plus an appendix for the CAD drawings. Your report should contain the sections:

1. Abstract - Provide a short abstract of your lab report. Please include the relevant parameters of your turbine such as the optimal torque and angular velocity and shaft power of your final design.

2. Objective - State the objective of the project, the constraints within which you designed your turbine.

3. Design Summary – Summarize how you went about designing and testing your turbine. It should be split up into sub-sections titled “1st Design Iteration”, “2nd Design Iteration” … “Nth Design Iteration”, and lastly “Final Design”. You should have at least one iteration and a final design. The “Final Design” is what you will enter into the contest, not necessarily the last iteration.

In each of these sub-sections, please write a paragraph describing the design and the basic rationale behind it. You should also refer to any CAD drawings in these paragraphs. The report does not need to include drawings for every iteration, but you must include the drawings and tables listed below for your final design. (CAD drawings may go in an appendix, so they can fill the entire page.)

• A CAD drawing of a single blade containing orthographic and isometric projections of the blade. (No hand drawings—this must be made using computer software.)

• A CAD drawing of the fully assembled turbine with all N blades containing orthographic and isometric projections. (No hand drawings—this must be made using computer software.)

4. Results – Summarize the results of your testing. This section should include:

• A torque/power curve for one of the design iterations. Use the “yyaxis” or “plotyy()” command to plot torque on the left vertical axis, power on the right vertical axis, and angular velocity in units of RPM on the horizontal axis.

• A torque/power curve for the final design. Use the “yyaxis” or “plotyy()” command to plot torque on the left vertical axis, power on the right vertical axis, and angular velocity in units of RPM on the horizontal axis.

• A table listing the optimal torque, angular speed, and power for all design iterations you tested. Be sure to indicate which design you ended up using in the contest as your “Final Design”.

5. Discussion - Discuss the performance of your final turbine design. How might you improve upon your final design?

Page 6: Experiment B11/B12 Turbine Design Procedureprumbach/AME20217/B11/F19_B11_B12_procedure.pdf · Experiment B11/B12 Turbine Design Procedure Deliverables: Checked lab notebook, Full

University of Notre Dame Aerospace and Mechanical Engineering AME 21217: Lab II Fall 2019

B11/12 – Turbine Design 6 Last Revision: 11/15/19

Appendix A

Figure 2 – Instructions for mounting the blades to the hub and Wind Trainer.

1) Set pitch angle to a value between 5° and 90°

2) Place hub on the steel rod with set screws facing toward you

4) Tighten set screws with a long hex key to secure the blade dowels

5) Mount fully assembled hub and blades in the wind trainer oriented so the wind hits the set screws.

3) Make sure dowels are fully inserted into holes on the hub

6) Use the short allen wrench to tighten the middle set screw onto the FLAT portion of the dynamometer shaft

Page 7: Experiment B11/B12 Turbine Design Procedureprumbach/AME20217/B11/F19_B11_B12_procedure.pdf · Experiment B11/B12 Turbine Design Procedure Deliverables: Checked lab notebook, Full

University of Notre Dame Aerospace and Mechanical Engineering AME 21217: Lab II Fall 2019

B11/12 – Turbine Design 7 Last Revision: 11/15/19

Appendix B

Equipment • Wind trainer • 12 spoke turbine hubs with 3/16” holes • 2mm Hex keys • 6” long, 3/16” diameter wooden dowels • 1/8” thick, 1” x 36” strips of balsa wood • 1/8” thick, 2” x 36” strips of balsa wood • 1/8” thick, 3” x 36” strips of balsa wood • 1/8” thick, 6” x 36” strips of balsa wood • Hot glue sticks • Hot glue gun • Cutting mats • Exacto knives • Box cutters • Straight edge • Combination square • Sand paper • Dremmel tool