Study Of The Aerodynamic Performance Of Offshore Twin Vertical Axis Wind Turbines

Offshore wind energy is considered to potential in the future,but the wind turbines there face more severe challenges than that on the onshore.So the cost of offshore wind power remains higher.Large megawatt wind turbines and floating wind turbine technology are regarded as two important ways to reduce the cost.The author proposes a novel floating twin vertical axis wind turbines(VAWT)concept for the future deep sea wind energy utilization.The VAWT have a lower center of gravity,a simpler structure,and the potential to scale up to larger sizes compared with horizontal axis wind turbine.However,the poor efficiency hinders its development.The twin vertical axis wind turbines proposed by the author uses the beneficial interaction between the VAWT as well as the deflector to improve the efficiency of wind turbines.This paper studies the aerodynamic performance of this novel vertical axis wind turbine and the main research contents are as follows:Firstly,the deflector applied to the twin VAWT is explored through the CFD simulation.The performance of twin VAWT is studied by the two-dimensional CFD simulation.Then the V-shaped deflector is proposed and studied to estimate its effect on wind turbine performance.It is found that the front deflector can improve the wind turbine performance most among the three configurations.Secondly,the twin VAWT performance with and without deflector is tested through the wind tunnel experiment.The twin VAWT is tested firstly to obtain the improved performance compared with the isolated wind turbine.Then the wind turbines' performance with deflector is accessed,including the effect of wind turbines' rotating directions and deflector's position on wind turbine performance.It is found that the performance of twin VAWT is improved at the high tip speed ratio,and the performance at low tip speed ratio is improved by adding the deflector.Finally,the three-dimensional CFD simulation is performed to study the wind turbine performance difference caused by the deflector.The CFD model is validated against the experiment data before.Then the effect of tip speed ratios,wind turbine rotating direction and deflector position on the wind turbine performance is analyzed by studying the flow field around the blade.It is found that the deflector is able to change the wind turbine performance by blockage effect and acceleration effect.The blockage effect can improve the blade stall at the low tip speed ratio,and the acceleration effect can enhance the local angle of attack and relative velocity to improve the wind turbine performance.The closer wind turbines can suppress the shedding vortex from the deflector,which reduces the unfavorable effect on wind turbine power output.