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A study emphasizing the effects of passive vortex generators (VGs) on aerodynamic characteristics of a NACA 4415 airfoil is presented. Both experimental and numerical works have been carried out on an array of VGs attached to a NACA 4415 airfoil. Lift and drag measurements are made at various angles of attack by using three-axis component balance system. On the numerical side, Reynolds-averaged Navier-Stokes (RANS) equations have been solved with ANSYS FLUENT 14.5 commercial code with fully structured mesh and three turbulence models (realizable k-ε, k-ω shear stress transport [SST] and the Spalart-Allmaras model) at Reynolds number Re = 2 × 10 5 .Parametric studies have been conducted to find out optimal configurations with respect to span-wise separation distance between VGs, along with their location along the chord. A very good agreement has been obtained between experimental and computational results indicating that this optimized configuration is robust for the considered parameters. It turns out that increasing the span-wise separation length increases the aerodynamic performances (lift-to-drag ratio) at low attack angles for which low parasitic drag is achieved but conversely degrades it at higher ones. For the stream-wise location along the chord, upstream position of VGs degrades the lift-to-drag ratio at low attack angles and conversely improves it at higher ones. KEYWORDS computational fluid dynamics, flow control, NACA 4415 airfoil, passive vortex generators, Spalart-Allmaras turbulence model, wind tunnel 1 | INTRODUCTIONOwing to the continuous increase in energy consumption and persisting demand from governments and citizens for a more sustainable energy production the wind energy has experienced considerable growth in the past decade.The prospects and main challenges of wind applications are to reach the target of 1000 GW of wind energy by 2030. 1 For the offshore market, this has led to race in building the largest wind turbines, but one now faces critical limits from a technical point of view along with prohibitive prices toward the goal to reduce the energy cost for the end-user (CoE). 2,3 For the onshore market, size upgrade is not a promising strategy owing to environmental issues related to higher noise levels and visual inconveniences. Therefore, for this latter market, engineers investigate the way to increase the aerodynamic efficiency from classical wind turbines. However, studying aerodynamic performance of full size wind turbine remains a difficult task since relevant metrology in rotating frame of such sizes is incredibly expensive and difficult. On the computational fluid dynamics side, their related large size 3-D highly turbulent flows around moving bodies are also very challenging, so very few works have been published up to now. 4

Abstract. The main subject of this work is the numerical study control of flow separation on a NACA 23015 airfoil by using wing cuff. This last is a leading edge modification done to the wing. The modification consists of a slight extension of the chord on the outboard section of the wings. Different numerical cases are considered for the baseline and modified airfoil NACA 23015 according at different angle of incidence. The turbulence is modeled by two equations k-epsilon model. The results of this numerical investigation showed several benefits of the wing cuff compared with a conventional airfoil and an agreement is observed between the experimental data and the present study. The most intriguing result of this research is the capability for wing cuff to perform short take-offs and landings.