Wind turbine has been attracted as the technology for clean and renewable energy and many kinds of the researches and the developments are performed. Cross-flow wind turbine has a characteristic of good self-starting, low noise and high stability. Therefore, it is expected as the small-sized wind turbine for urban district. But the maximum power coefficient of the cross-flow wind turbine is extremely low as 10%. Wind in an urban region and a coastal place has a prevailing wind of two directions to occur in a specific condition frequently. Then, a casing suitable for this prevailing wind was designed in this research and the effect of the casing was investigated by experimental and numerical analysis. In the experiment, a wind tunnel with a square discharge 500mm×500mm was used and main flow velocity was set as 20m/s to reduce the influence of measurement error on performance. A torque meter, a rotational speed pickup and a motor were assembled with the same axis at low position of a test wind turbine which was set vertically and rotational speed and tip speed ratio were changeable by a rotational speed controller. The casing was set around the cross-flow rotor and flow distribution at the rotor inlet and the outlet was measured by a one-hole pitot tube. The maximum power coefficient was obtained as Cpmax = 0.19 with the casing, however as Cpmax = 0.098 without the casing. And it was clarified that the inlet and the outlet flow condition was improved by the casing. In the present paper, in order to improve the performance of a cross-flow wind turbine, a symmetrical casing suitable for the prevailing wind of two directions is proposed. Then performance and internal flow condition of the cross-flow wind turbine with the casing is clarified. Furthermore, the influence of a symmetrical casing on performance is discussed and the relation between flow condition and performance is considered.

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