Experimental Study of Shrouded Micro-Wind Turbine

Shrouding (diffuser augmented) horizontal axis micro-wind turbine has been shown to be an effective way to potentially improve the performance of micro wind turbine for applications in built environments. It is well understood that the degree of the performance enhancement depends on several factors including the diffuser shape and geometries, blade airfoils, and the wind condition at the mounting site. The effect of diffuser shape and geometries is reported in this paper. Performance of diffuser with three different geometrical features namely: straight diffuser, nozzle-diffuser combination, and diffuser-brim (brimmed diffuser) combination have been investigated. This paper aims to compare the performance of bare and diffuser augmented turbine; and investigate the effect of the diffuser geometrical parameters: diffuser lengths (L/D = 0.63 to 1.5) and flange heights (H/D = 0 to 0.2). Tests confirmed that placing the micro turbine model inside a shroud can substantially improve its performance. The diffuser only shroud improves the performance by 60% compared to the bare turbine and the nozzle-diffuser enhancement of 63% is slightly better than diffuser only. The improvement with brimmed diffuser also shows substantial performance enhancement. Increasing the diffuser length (L/D) does not affect the optimum Cp of the wind turbine but shifts the performance curve and the optimum Cp to higher tip-speed-ratio, λ. But adding brim (flange) at the exit plane of the diffuser increase the performance, Cp as well as reduce the cut in speed and shift optimum λ to higher value. The finding from this work demonstrates that shrouding micro wind turbine not only improves its performance but also points out how diffuser geometrical features (L/D) and/or (H/D) can be used to design a turbine with performance curve to suit the location.