Vortex interaction in the wake of a two- and three-bladed wind turbine

Jan Bartl,W Ludwig Kuhn,Franz Mühle,Thomas H Hansen,Lars Sætran

doi:10.1088/1742-6596/1669/1/012027

Abstract

The vortex interaction in the wake behind a two- and three-bladed model scale wind turbine is investigated. The two rotors have equal solidity, and produce similar power and thrust at the design tip speed ratio. Phase-averaged quantities of the wake flow from one to four rotor diameters behind the turbines are measured in a wind tunnel. It is found that the two-bladed turbine has slower wake recovery than the three-bladed turbine, and a larger velocity deficit is produced in the far wake. The tip vortices behind the two-bladed turbine is more stable than behind the three-bladed turbine, and the vortex structures exist further downwind. In a wind farm, this could reduce the power production and increase fatigue loads for the turbines operating in the wake flow, especially during stable atmospheric conditions.

Highlights

Given the possible advantages of significantly lower cost and reduced weight, two-bladed wind turbines have recently been given renewed interest for application in the offshore environment
It is found that the two-bladed turbine has slower wake recovery than the three-bladed turbine, and a larger velocity deficit is produced in the far wake
Two-bladed rotors are known to experience higher cyclic loads than three-bladed turbines, and these problems stem from the imbalance of having only two blades when the turbine is exposed to a wind shear or a tower shock impulse [2]

Summary

Introduction

Given the possible advantages of significantly lower cost and reduced weight, two-bladed wind turbines have recently been given renewed interest for application in the offshore environment. In a numerical study performed by Duquette and Visser [6], the effect that the blade number and the rotor solidity has on the turbine performance is investigated. They computed a larger power production for the turbine when increasing the number of blades and applying a large rotor solidity. In another experiment performed by Duquette et al [7] these findings where partly confirmed, but in contrast to the simulations a decrease in power is observed when the number of blades on the turbine is larger than three

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Discussion

Conclusion