Effect of blade tip on torque characteristics of circular cylinder blade wind turbine driven by longitudinal vortex

Abstract

In a circular cylinder blade wind turbine driven by a longitudinal vortex, the torque characteristics of the turbine are greatly affected by the flow field at the blade tip. In general, wind turbines reduce drag by making the blade tips thinner. However, because this wind turbine uses a cylinder as a blade, it is important to control the flow field at the blade tip. From the experiments, it was found that the torque coefficient can be increased by attaching the endplate to the blade tips, and the rotational force can be obtained stably up to very low rotation speeds. The installation of fairing or endplates in circular cylinder blade wind turbines enables stable rotation at low speeds even under high loads, and also reduces drag at high speeds and increases the maximum speed. In the case of a disk-shaped endplate, the torque coefficient can be increased by up to 20 % by attaching an endplate with a diameter 2.5 to 3 times the diameter of the cylinder to the outer blade tip only. The L-type endplate has the effect of shifting the characteristics to the higher rotation side than the disk-type, and increases the torque coefficient at the same tip speed ratio. However, the lower limit of stable rotation becomes higher, and as a result, the value of the maximum torque coefficient obtained at high load decreases. If the endplate attached inside has a negative effect on the stable formation of the necklace vortex, it will inhibit the rotation at a low speed due to high load, making it difficult to obtain high torque.