A sailwing vertical axis wind turbine for small scale applications
The use of sailwing aerofoils in vertical axis wind turbines has been investigated. It was anticipated that this could make vertical axis turbines more suitable for water pumping and that this might help to meet the need for a cheap pump for irrigation existing in many parts of the world. A numerical analysis of the theoretical performance of such a turbine, using existing aerodynamic data for simply constructed sailwings, has been made. This gave an improved understanding of the operation of such turbines but showed a need for further aerodynamic data. Some new wind tunnel tests of sailwings are described in which the effect of pre-tension was investigated and four different fabrics were tested. The results are presented for angles of incidence up to 180 degrees and compared with previous data. With the fresh data, new performance predictions were made which led to the design of a two metre diameter prototype turbine. This used an inclined blade configuration with a guyed top bearing. Canvas was used for the sails. It was predicted that the turbine performance would be significantly affected by windspeed. The turbine was built and later tested in the open air. An acceleration test method was used and the tests generally confirmed the predictions. The averaged starting torque coefficient was about 0.07; the averaged peak power coefficient was about 0.1 at a tip speed ratio of 1.4. Consideration has been given to improving windpump system efficiency by improving the gust energy utilisation. Some tests of a diaphragm pump are described in which inertia flow effects were used. A pair of such pumps were later connected to the prototype turbine. A number of problems were encountered and satisfactory operation was not achieved in the time available. The main problem was the cyclic driving torque produced by the three bladed turbine.