The type of airfoil used in this study is NACA 0015 with 150 mm of chord length. This study aims to determine the optimum position and geometry of stall strips (SS) to control sudden fall of lift in wind turbine blades. The multi blowing holes with velocity improved the aerodynamics properties.The multi blowing holes and single blowing hole thesame effect onpressure distribution coefficients. Both studies (experimental and numerical) were done at low Reynolds number (Re=4.4x10 5) and all models have chord length 0.27m.The experimental investigations and CFD simulations have been performed on the same geometry dimensions, it has been observed that the flow separation on the airfoil can be delayed by using velocity blowing (30m/s) on the upper surface. A numerical study was done by using ANSYS Fluent software version 16.0 on three models of NACA 0015, the first one has backward-facing step without blowing, the second with single blowing holes and the third have multi blowing holes technique. The tests were done over two-dimensional airfoil in an open circuit suction subsonic wind tunnel with flow velocity 25m/s to obtain the pressure distribution coefficients. The study was divided into two parts: a practical study through which NACA 0015 type with a backward-facing step (located at 44.4% c from leading edge) on the upper surface containing blowing holes parallel to the airfoil chord was used. The flow field over airfoil has been studied both experimentally and computationally. The aim of this paper is to control the flow separation above backward-facing step (BFS) airfoil type NACA 0015 by blowing method. Compared to standard NACA 0015 airfoil, a significant improvement in the lift coefficient for multi-element NACA 0015 was noticed especially at the angle of attack (6°,14° and 18°) while slight improvement was noticed in the lifting coefficient for the other two models (bumps NACA 0015, and a backward-facing step NACA0015) at AOA 14 degree. As a result, the geometrical modification influences on the aerodynamic properties of NACA 0015 was investigated. The CFD software ANSYS FLUENT version 17.1 was used for the computations in the present study. Case II: the coefficient of pressure, coefficient of lift, the contour of static pressure, and the velocity contour for standard NACA 0015(chord length c=1m) were calculated and compared with three geometrical modifications NACA 0015 airfoil. Case I: the numerical analysis method data for the coefficient of lift of standard NACA 0015 (baseline case study) is compared to the previous experimental data. The research focuses on two cases (at different attack angles from 0 to 18 degrees with Re=1.65x10 6). Using SST (Shear Stress Transport) turbulence model and compared with standard NACA 0015 was the performed methodology. The study was performed by simulating three geometrical modification airfoils (bumps NACA 0015, multi-element NACA 0015, and a backward-facing step NACA0015). The airflow around two-dimensional standard NACA 0015 airfoil effect was studied and analysed.
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