Design and aerodynamic performance analysis of a finite span double-split S809 configuration for passive flow control in wind turbines and comparison with single-split geometries

Abstract

With the previous knowledge of the effectiveness of single-split blades, questions arise about the effectiveness of a double-split configuration on horizontal axis wind turbine. To shed light on this question, a 3-D double-split finite-span configuration with S809 airfoil profile is designed based on the results of unsteady DES simulations of two families of single-split configurations. Firstly, the two 3-D single-split families with four different values of split width are simulated at angles of attack (AOA) up to 25°. Secondly, a finite span double-split model is designed based on the single-split geometries with the highest aerodynamic performances. It has been found that the double-split configuration had the poorest performance for 0°<AOA<17°; however, at 17°<AOA<22°, the double-split model showed the highest performance. Analyzing the time-averaged streamlines showed that excessive injected flow at low AOAs as well as the formation of separation bubbles inside the split channel were two main negative factors that severely reduced the performance of the double-split geometry. Also, findings revealed that using optimum cases of single-split geometry does not result in an optimum double-split geometry. Lastly, considering all findings, a conceptual selective (controlled) flow control method that led to a considerable increase in the aerodynamic performance of the double-split geometry has been proposed and discussed.