| The Straight-bladed vertical axis wind turbine have received more and more attention and developed rapidly, but when it is set in a cold region, it starts to get ice accretion on it in winter. Presently, The studies of icing effect on aerodynamic characteristics of wind turbine were few, and the study on icing for staight-bladed vertical axis wind turbine was almost nothing. However, the author's research team have some experiences of research in this field, so this study chose icing on the staight-bladed vertical axis wind turbine and blade airfoil as the study object, experiment outdoor, numerical computation and wind tunnel test were combined as the study method to investigate the ice accretion on surface of blade and icing effect on aerodynamic characteristics of staight-bladed vertical axis wind turbine and its blade. The following are the main contents and results in this study:Frost, rime and glaze were 3 results in the experiment outdoor, and the relationship between them and the wind speed, wind direction, temperature and humidity of air was analyzed. It turned out that frost happened in a low temperature, high humidity of air and low wind speed condition; rime was easily to happen in a high wind speed and humidity of air condition, when the temperature from -10°C to 0°C; In the same condition of rime, glaze happened as well, and cold rain and wet snow helped a lot.In the study of icing on the blade of straight-bladed vertical axis wind turbine, numerical computation and wind tunnel test were used. The numerical computation simulated the icing progress in different conditions, calculated the flow field, blade shape and aerodynamic characteristic parameters before and after ice accretion on the blade. The icing condition on the surface of blade in different wind speed, humidity of air and angle of attack were gotten in the wind tunnel test, and lots of photographs of ice accretion on blade were taken. The following were the conclusion:1) The extreme cold water droplet in the wind and the wind speed were the key factor that affected the ice accretion on the surface of the blade, and they were proportional to ice accretion mass; water droplet flux decided the ice accretion mass in a low wind speed, and wind speed became more important for icing when it increased. When the front edge was upwind, water droplet was the key factor to the ice accretion thickness, while the tail edge was upwind, water droplet and wind speed were less important for ice accretion on the tail edge region of blade. When water droplet flux was little, it had a linear relation with ice accretion area, but when it was large, the ice accretion became complex and unpredictable. The higher wind speed helped more water droplets to adhere to the blade easily and made the whole icing progress faster. But if the intensity of ice was not enough, the higher wind speed would caused a larger wind pressure and destroyed the ice structure.2) The different angle of attack changed the upwind area of blade and its flow field, which caused the thickness and area of ice accretion changed. The law of icing was different around front edge and tail edge, when tail edge was upwind, icing only occurred in a small area of tail edge; while front edge was upwind, the max icing thickness didn't change with the angle of attack, the thickness of ice in front edge was usually larger than that in tail edge. Generally speaking, the ice accretion area and mass increased as the angle of attack did, in some case, the ice accretion area could be 30% of the area of blade aerofoil.3) The drag coefficient increased and lift coefficient decreased after icing, and the ratio of lift to drag reduced, that weakened aerodynamic characteristics of blade. The max variable of drag coefficient was 1.1513 and max variable of lift coefficient was 1.9806 in the wind tunnel test. The same conclusion could be summed up in numerical computation.In the study of icing on wind turbine, wind tunnel test was carried out to get torque,icing mass and ratio of icing mass to water mass.The water droplet flux could decide the icing mass but not the ratio of icing mass to water mass; In a low tip speed ratio, the flux had a linear relation with icing mass, while in a high tip speed ratio, the icing mass couldn't be predicted. The aerodynamic characteristic of wind turbine were weakened after icing, both higher wind speed and larger flux could weaken aerodynamic characteristic of wind turbine strongly.The results obtained by this study can be used as the experimental and theorical reference for the fundermental research of Straight-bladed vertical axis wind turbine.It is also useful for the development of wind energy utilization system suitable for cold regions and for the anti-icing and de-icing technologies. |
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