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Effect of Boundary Layer Tripping on the Aeroacoustics of Small Vertical Axis Wind Turbines

Small wind turbines are investigated as a possible solution for using wind energy at small scales in urban and suburban areas. Most turbines are suffering from a low aerodynamic performance due to turbulent and complex wind situations in cities. Therefore, increasing aerodynamic performance and reducing noise is an important factor to design small wind turbines. In order to optimize such turbines with respect to noise and efficiency it is important to understand the physical mechanisms. Measuring acoustic in urban environment it is hardly possible to obtain reproducible results, which are necessary for a comprehensively and profoundly investigation. Therefore, experimental studies have to been performed in anechoic wind tunnels. Those tunnels are mostly limited in size, which makes it quite difficult to investigate full small wind turbine models. Hence a model scale has to be used in order to measure the power and acoustic performance. For comparing the model scale results with original turbines, the same flow conditions around the airfoils are necessary. Due to the smaller size of the model scale the relative velocities of the blades are less, which can result in a laminar boundary layer. In order to force transition from laminar to turbulent, boundary layer trips can be used. The focus of this study is to examine and quantify the effect of boundary layer tripping on the aeroacoustics in case of small vertical axis wind turbines.