Investigation Of Turbulence Effect On The Aerodynamic Performance Of A Vertical Axis Wind Turbine Through Large Eddy Simulation

With the continuous acceleration of modernization,traditional petrochemical energy and other non-renewable energy can no longer meet the needs of production and living.Moreover,petrochemical fuel will inevitably cause serious environmental problems.Wind energy,as a clean and renewable energy,has seized more and more attention.Wind turbine is the most effective way to harness wind energy.Vertical axis wind turbines(VAWTs)play an important role in urban wind power production because of their advantages such as low noise,low maintenance cost and ability to operate in turbulent environment.Note that urban environment is characterized by the instability of wind speeds and high levels of turbulence.However,previous studies on the aerodynamic performance of VAWTs mainly focused on smooth flows.With this consideration,this study examines the aerodynamic performance of VAWTs in turbulent environment by computational fluid dynamics(CFD)simulations.Independence studies of the computational domain size,mesh density,time step and calculation duration were carried out.Considering both the calculation accuracy and time efforts,the optimal three-dimensional model of large eddy simulation for calculating the aerodynamic performance of the VAWT was thus determined.The curves of power coefficients with blade speed ratios(BSRs)were drawn and compared with the results of previous wind tunnel experiments.The high consistency of the comparison results verified the validity of the large eddy simulation(LES)model adopted in this study.Based on the method for the simulation of turbulent inlet proposed by previous scholars,a homogeneous turbulent wind field was generated.The aerodynamic performance of the VAWT in turbulent flows was studied and compared with that in smooth inflows.The results showed that the aerodynamic performance under turbulent flows was very different from that under smooth flows.The effect of turbulence on the aerodynamic performance of the VAWT was analyzed by comparing the aerodynamic loading on turbine blades in turbulent and smooth flows.The dynamic stall behaviors of blades were also examined in both flow regimes.Results found that wind speed fluctuations of turbulence changed the peak values of torque coefficients and the occurrence of dynamic stall in each revolution.This led to the great fluctuations in power coefficients in each revolution compared with that in smooth flows.In general,the existence of turbulence improved the power coefficients of the VAWT and increased the power generation efficiency.The average power coefficients of the VAWT increased to different degrees in turbulence flows under different BSRs.By comparing the curves of power coefficients with BSRs,it was found that the turbulence had a slight effect on the rated BSRs.When turbulence intensity was 15%,the rated power coefficient increased by 7.3%.In addition,the LES analyses of the VAWT under different turbulence intensities and different average wind speeds were carried out.The fluctuation range of the power coefficients was larger with the increase of turbulence intensity,but the average power coefficient did not increase with the increase of turbulence intensity.Moreover,when the average wind speed was less than 10m/s,the average power coefficient changed obviously with the increase of the average wind speed.However,the average power coefficient did not change significantly when the average wind speed was greater than 10m/s.