Numerical investigations of two Darrieus turbine rotors placed one behind the other with respect to wind direction

摘要: Vertical axis wind turbines (VAWTs), in particular Darrieus turbine has attractive characteristics of utilizing wind from different directions for power generation, compact design, easy installation, and maintenance. It appears promising for low wind speed and urban area conditions. The VAWTs wakes intrinsically unsteady, this unsteadiness comes from the instantaneous change of local angle of attack with respect to azimuthal variation. The unsteadiness may appear in many forms as blades wake interaction, time variation vorticity strength etc. As most of VAWTs are installed on building rooftops, many turbines could be close to each other. There is a high possibility based on wind direction that one turbine operates in the wake of another. Therefore, in this paper the aerodynamic performance of two Darrieus turbine rotors placed one behind others with respect to wind direction is investigated using CFD. The rotors are two bladed with NACA0021 airfoil section and rotor radius of 1 m operating at a uniform wind speed of 8 m/s. Before investigating this configuration, the results of numerical simulations for single rotor are validated against published experimental results. The investigation indicates that the second turbine shows better performance if the first turbine operates at a high-speed ratio. If the first turbine operates at a low-speed ratio, the performance of the second turbine worsens.