Experimental and numerical investigations of flow fields behind a small wind turbine with a flanged diffuser

Experimental and numerical investigations were carried out for flow fields of a small wind turbine with a flanged diffuser. The present wind-turbine system gave a power coefficient higher than the Betz limit (=16/27) owing to the effect of the flanged diffuser. To elucidate the flow mechanism, mean velocity profiles behind a wind turbine were measured using a hot-wire technique. By processing the obtained data, characteristic values of the flow fields were estimated and compared with those for a bare wind turbine. In addition, computations corresponding to the experimental conditions were made to assess the predictive performance of the simulation model presently used and also to investigate the flow field in more detail. The present experimental and numerical results gave useful information about the flow mechanism behind a wind turbine with a flanged diffuser. In particular, a considerable difference was seen in the destruction process of the tip vortex between the bare wind turbine and the wind turbine with a flanged diffuser.