Unsteady Aerodynamic Simulation of Horizontal Axis Wind Turbine Blade Mohamed A. Sayed 1 , Ayman A. El-Badawy 2 * 1 Dept. of Mechatronics Engineering, German University in Cairo, Cairo, Egypt (Email: mohammed.sayed@guc.edu.eg) 2 Dept. of Mechanical Engineering, Al-Azhar University, Cairo, Egypt And Dept. of Mechatronics Engineering, German University in Cairo, Cairo, Egypt (Email: ayman.elbadawy@guc.edu.eg) Abstract In this paper, steady and unsteady aerodynamic simulations were performed based on the Blade Element Momentum theory (BEM) by using an open source code (AeroDyn) developed by the National Renewable Energy Laboratory (NREL). The reference wind turbine used in the simulations is the Controls Advanced Research Turbine (CART) which is a machine rated at 600 kW for a specific airfoil family set. The aerodynamic steady wind simulations obtained using AeroDyn are verified using finite element analysis. To be able to capture the un-steady effect of wind on the blade, a Kaimal turbulence power spectral density model has been used. The normal and tangential force components are determined due to the unsteady wind. The dynamic coefficient of lift has also been obtained in the stall region. Keywords: BEM, Unsteady Aerodynamic, Wind Energy. 1. Introduction The unsteady aerodynamics of wind turbines is one of the most incentive issues in wind energy research and development [1], [2]. The aerodynamic analysis of the Horizontal Axis Wind Turbine (HAWT) may be performed either by the solution of the full Navier-Stokes equations or the BEM. Incompressible Navier-Stokes analyses have been used by Sorensen and Michelsen [3]. Sorensen et al. [4] have reported excellent Navier-Stokes simulations for the National Renewable Energy Laboratory [NREL] Phase VI rotor tested at the NASA Ames Research Center. The effect of transition and turbulence models on the Navier-Stokes predictions has been studied by Xu and Sankar [5] and by Benjanirat et al. [6]. The unsteady BEM has also been widely used for aerodynamic simulations of wind turbines [7], [8]. In this paper, steady and unsteady aerodynamic simulations were performed based on the BEM. The reference wind turbine used in the simulations is the CART[9]. The blade profiles were selected from the NREL airfoil families. 2. Steady Simulation of CART0 Wind Turbine To obtain aerodynamic response of the CART wind turbine, the NREL wind turbine airfoil family set: S816 blade profile for the tip, S817 blade profile for the primary and S818 blade profile for the root has been selected. This family set is recommended for a wind turbine rotor diameter of 30-50 meters [10] and the rotor diameter for the CART wind turbine is 42.7 m. To avoid the sudden change in the cross section area of the different blade elements, blended airfoils were used between root and primary, primary and tip in all simulations. For a given local pitch angle distribution (Figure 1) which represents the initial pitch = 0° + given twist angle, the resulting angle of attack distribution for a constant applied wind field of 12 m/s is shown in Figure 2. This decaying distribution is due to the variation in the velocity distribution along the blade length as well as the change in the calculated axial induction factor shown in Figure 3. The axial induction factor indicates the degree with which the wind