The Development Of A Self-optimising Windpump

Abstract

Windpumps marketed presently do not run satisfactorily, because it is difficult to match the pump load to the rotor power. This project was set out to develop a windmill which would continuously match the pump load to the rotor power automatically. A four-bladed windpump model was built and tested in a wind tunnel, to simulate a mechanical power transmission coupling, which can match the pump load to the rotor power automatically, and hence achieve optimum efficiency at all wind speeds. Experiments were performed for blade pitches between 200 and 700 and wind tunnel air speeds between 2.3 mls and 14.0 m/s. At each testing speed the model was run, as the brake load was varied, until a steady state situation was reached, when the rotor would be running at optimum conditions. \ It was found that the coefficient of performance was a function of the air speed, the angle of blade pitch and the tip-speed ratio. For optimum operating conditions the pitch angle and tip-speed ratio were 50° and 2.9 respectively The highest efficiency for the model was recorded at a tunnel air speed of 12.4 m/s. From the model tests, it was found that a four-bladed full size windmill would have the highest efficiency at a pitch angle of 500, a tip-speed ratio of 2.9 and a wind speed of 10 m/s. The highest efficiency would be appoximately 45%. It was found advisable to design the windpump to run between 5 and 15 m/s. As wind speeds vary between 5 and 15 m/s, it is envisaged that efficiency will first rise from 20% at 5 m/s to 45% at 10 mis, then it will reduce to 30% at 15 m/s. Averaged over a long period, the average efficiency will be higher than is usually the case. The amount by which efficiency will be improved will be determined in further research work