We devise an undergraduate experiment to evaluate the wind turbine power coefficient. The apparatus features a commercial miniature rotor hub that allows both blade replacement and adjustment of the pitch angle. The blades are 3D printed. Three pedagogical objectives are emphasized: (1) the demonstration of a practical application of rotational mechanics, (2) the illustration of wind harvesting by parameter optimization, and (3) the appreciation of where the unharvested wind energy goes. Analysis of the student performance shows that the three objectives are partially achieved.
REFERENCES
Horizon FCJJ-29, Horizon Educational Group, Horizon Fuel Cell Technologies (US$120).
RS Component NMB radial ball bearings (US$9 for two), ThorLab CP1TM06 cage system (US$36 for two plates).
ThorLab mounting bracket A1-780 (US$18).
The equivalence hinged on the consistency among the student setups and the instructor setup, viz., the same coefficient of friction between the string and the shaft. Details of the evaluation of the frictional torque are given in the section “Measure the moment of inertia of the rotor” of the supplementary material. In principle, students could make that measurement but it would be time-consuming.
Interested readers are welcome to email one of us, N. Cheung, at [email protected] for a copy of the lab manual.
The derivation of the Betz limit can be found in Section 15.6.5 of Ref. 1.