The wind turbine has become more popular in recent years, but on the other hand, the developments of small wind-turbine have been legging behind. Because, the energy density of wind is small, since the efficiency of the main part of a wind turbine is very low. The construction costs become comparatively high-priced. Then, the main part of this subject is to show that, by collecting and sucking out more winds, a wind turbine is made to pass many winds and the new cross-flow wind turbine that increases an output coefficient is proposed. The cross-flow wind turbine has high torque and low speed characteristics and the structure are very simple. So, it can be used in a large wind velocity region. However, even if the power coefficient is high, it is about 10%. The purpose of this paper is to show how we can improve the power coefficient by applying a casing, which has a nozzle and a diffuser. This research was made to clear up fundamental characteristics of the interaction between outer flow and inner flow. Three kinds of cross-flow wind turbines were designed. The nozzle and diffuser have been designed suitable for the performance of wind turbine. The flow simulations by CFD have been carried out for various types of casings at 20 m/s with Fluent Ver5.0. All Wind tunnel experiments were performed at 20m/s. The case of casing 2, which have plate arranged near the separation point of cylinder, also experimented. The rotor that is settled in the casing 1 shows a larger power coefficient than the case without a casing. The casing of the cross-flow turbine makes a pressure difference between inflow and outflow. The pressure difference increases the mass flow rate. Therefore much more wind passes through into the cross-flow turbine. In this experiment, the power coefficient increased 1.5 times in the case with casing. A still higher output coefficient could be obtained in the case where it is shown by the casing 2.

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