Numerical simulation on unsteady flow field of straight bladed darrieus wind rotor

In order to know more information about the complex turbulent field in vertical axis Darrieus rotors, the unsteady k-ω turbulence model and sliding mesh technique were used to model the aerodynamic characteristics and two-dimensional flow field in this kind of wind rotor with straight blades of NACA0012 airfoil. The aerodynamic flow field around the blades and torque characteristics of rotor at different rotational speeds were investigated. The flow fields in the rotors at different time instances i.e. in different azimuth angles, were presented, the results revealed that the relation angle of attack with azimuth angle is not a sinusoid. The torque curves indicated that a maximum torque was generated when the blades were at the 90° azimuth angle, the blades at downstream of the rotor had a near zero or even a small negative torque, suggesting the angles of attack there were very small. At the same wind free stream velocity, the wind velocity in the rotor was reduced with increasing rotational speed. The torque curves of upstream blades showed a maximum torque at a rotational speed when the speed was increased, however, the torque on downstream blades decreased steadily and exhibited a conside rable variation. The contrast of numerical results and test results prove that the turbulence model with slip grid technology can reflect the flow field in a vertical Darrieus wind turbine with straight blades.