Testing : Wind tunnel test intro | tunnel equipment | tunnel results, [pg2], [pg3] | tunnel conclude |
Multiple fans test intro | fan equipment | fan results, [pg2], [pg3], [pg4] | fan conclude

4. MULTIPLE FANS TEST - CONCLUSION

In the inertia acceleration testing method, the rotor model was tested with 3 fans under average wind speed of 4.66, 4.03, and 3.66m/s. The highest recorded Cp is 6.7% when operating under the highest wind speed. The corresponding optimum tsr is 2.6 while the maximum tsr is 3.3. The Cp and Ct increase with the wind speed but the optimum and maximum tsr remained quite constant. Main sources of errors were highly fluctuating wind from fan, rpm reading from the slow refresh rate tachometer, and discretization error when calculating angular acceleration.

In the band brake testing method, the model was only tested for one wind speed. The highest recorded Cp is 7% when operating under wind speed of 4.25m/s. The corresponding tsr is 2.75 while the maximum tsr is 3.3. Only half of the performance curves can be obtained from this method. The result might be marred by critical errors caused by high rpm fluctuation and slow deceleration respond besides the wind quality problems.

Both inertia acceleration and band brake testing result did not agree well as the performance measured from the band brake was higher than inertia acceleration method. The inertia acceleration method is regarded as a better method because of less critical errors, complete curve, shorter testing time, easier procedure, and less equipment.

The effect of number of fans was also studied. The optimum and maximum tsr decreased with decreasing number of fans but the self-starting ability improved. The bigger number of fans resembles the wind tunnel condition more because of bigger area of coverage.

The study of performance trend with wind speed can be improved by increasing the wind speed range. The inertia acceleration method can be improved by improving tachometer measurement, increase number of reflective tape per revolution, and increasing rotor inertia. The band brake needs lower inertia rotor for faster respond in testing. The uniformity of the brake friction should also be studied.

REFERENCES

Blackwell, B. F., & Sheldahl, R. E.(1977). Wind tunnel performance data for the Darrieus wind turbine with NACA 0012 blades. Sandia Laboratories Energy Report. SAND76-0130.

Grylls, W., Dale, .B, & Sarre, P. E.(1978). A theoretical and experimental investigation into the variable pitch vertical axis wind turbine. Proceedings of second international symposium on wind energy systems. pp.E9-101-118.

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.

Last updated at November 6, 2002
Comments are welcomed