Effect of leading-edge protrusion shapes for passive flow control measure on wind turbine blades

In the present study, protrusions in the leading edge of the NACA 4415 airfoil were incorporated as a passive flow control measure on the wind turbine blades. Three airfoil models: unmodified leading-edge (ULE), spherical leading-edge protrusion (SLEP), and triangular leading-edge protrusion (TLEP), were investigated experimen-tally. Thereafter, CFD investigations were carried out using ANSYS 14.0 simulation tool to observe the flow characteristics around the airfoils. Further, LEP-based passive design was applied on a horizontal axis wind turbine (HAWT) to investigate its performance. An amplitude (A) of 1% of the chord length (C) was considered as the height of protrusion, while a distance of 0.25C was maintained between the protrusions to fabricate the experimental models. The study was performed at a low Reynolds number (Re) of 1.5 x 105 for a wide angle of attack (alpha) of 0 degrees -20 degrees. The experimental results demonstrate that the SLEP model has a higher lift coefficient at alpha >= 18 degrees, whereas the TLEP model performs poorly when compared with the ULE model. The instantaneous lift coefficient plot indicates that the SLEP model generates a more stable force at a higher angle of attack. The computational analysis reveals that a larger primary circulation (extended till 0.2C) is observed in the ULE model at a post-stall angle of attack (alpha = 18 degrees), indicating early flow separation. Whereas, in the SLEP and TLEP models, it is extended to 0.70C and 0.54C, respectively, indicating the best flow controlling measures achieved by using the SLEP model. The investigations of HAWT rotors with LEP revealed that SLEP HAWT exhibit 8.2% more power coefficient than ULE HAWT.