4. WIND TUNNEL TEST - CONLCUSION
The testing in wind tunnel had to be done in a nonstandard way, as the
rotor was not able to operate at the highest wind speed. The opening at
the tunnel wall was opened deliberately during the testing which produced
faster wind but with curved direction. The effect of blockage in tunnel
was not studied.
The rotor produced highest maximum Cp of 4% at the wind speed of 4.11m/s.
The corresponding optimum tsr is 2.75. Maximum tsr is 3.25. When the wind
speed increased, both Cp and Ct increased. The maximum tsr also increased
with wind speed. The Ct peaked slightly earlier than Cp. The rotor was
not able to accelerate without assistance from stationary to the maximum
rpm. These result were measured using inertia acceleration method. The
errors in the testing are the highly restricted rotor wake and the disturbance
from turbulent wind.
Comparisons with the fans testing result show that the rotor performed
even worse in tunnel. The Cp and Ct were lower and the tsr operating range
was shorter. In addition, the rotor lost the ability to self-start in
wind tunnel. The reason the rotor performed better with fans might be
the unrestricted wake expansion under fans environment and unfavourable
wind in the tunnel as the counter wind half was blew harder. The result
from the tunnel was considered more accurate as the quality of wind was
way much better compare to the fans.
The result from the tunnel can be improved by increasing the range of
wind speed, avoid taking measurement from inside of the tunnel, and using
faster or automatic recording tachometer. To be able to use the wind tunnel
in standard way, the current model will have to be modified to higher
solidity or simply build a new bigger model. Both ways will increase blockage
and limit wake expansion. If the current model is to be tested in a faster
tunnel, special attention should be given to the bending of the airfoil.
REFERENCES
Musgrove, P. J., & Mays, I. D. (1978). Development of the variable
geometry vertical axis windmill. Proceedings of second international symposium
on wind energy systems. pp.E4-39-60.
Jesch, L. F., & Walton, D. (1980). Reynolds number effects on the
aerodynamic performance of a vertical axis wind turbine. Proceedings of
third international symposium on wind energy systems. pp.G1-323-332.
|
