Numerical Study On The Wake Characteristics Of The Horizontal Axis Wind Turbine

Nowdays, with the rapid development of industry and technology, the demand for energy is increasing, energy depletion and environmental pollution has become inceasingly serious, the whole world is vigorously developing renewable and clean energy sources. Wind energy is a renewable and clean energy source, the development and utilization of wind energy is gradually mature. Wind turbines are devices that convert wind energy into electrical energy, the ability to catch the wind of wind turbine airfoil is the key of wind power generation, at the same time, the changing of wind speed and wind direction will also have a great influence on the power out put and wake characteristics of wind turbine. Wind turbine working environment is always changing, so it is very important to study the steady and unsteady aerodynamic characteristics of two-dimensional airfoil and three-dimensional wind turbine,which is significant to the power generation efficiency and service life of wind turbine.First, for the study of two-dimensional wind turbine blade airfoil, the dedicated airfoil for wind turbine is studied in full scale, the static case of different angle of attack and unsteady dynamic condition of airfoil oscillation is calculated by simulation. The static simulation results show that, the simulated pressure distribution is in good agreement with the experimental pressure distribution in steady state; the flow is mainly attached to the surface of the airfoil at small angels of attack and the flow begins to be separated when the angle of attack is 10°and the separation vortex is separated from the surface of the airfoil when the angel of attack is 20°. the dynamic simulation of airfoil oscillation results show that, the flow separation can be delayed in the dynamic case, the dynamic stall effect becomes more obvious with the increase of the mean angle of attack, the amplitude and the attenuation frequency.Second, the NREL 5MW wind turbine is studied at steady case of different velocity and unsteady case of dynamic inflow. The steady case of different results show that the wind speed is higher, the easier to produce strong rotation of airflow near the blade tip at airfoil surface, and there is a delay effect about load distribution on the rotating airfoil with the same case of static airfoil. The dynamic inflow will change the position and structure of the wind turbine near wake vortex; the wind turbine wake velocity is almost back to the mainstreamvelocity at 4D under vertical wind shear, extreme vertical wind shear and the gust of wind is 6D, the wake velocity is close to mainstream velocity at 10 D under wind direction changing. It is important to consider all kinds of wind conditions at select the wind field address, the longitudinal distance of the downstream wind turbine is6 D and above.