Study Of Wake Effects In Offshore Wind Turbines

In wind power systems,wake effects of turbines can cause a decrease in downstream wind speed,resulting in reduced power output from turbines located in that area.Furthermore,increased turbulence in the wake region can impose instability on turbines and shorten their lifespan.As wind farms move towards ocean environments,where turbulence intensity is lower,wake effects become more severe.To address these issues,3D numerical simulations were conducted for both single-and double-turbine setups to study velocity distribution in wake fields and their effects on turbine output power.The main objectives were:(1)Numerical simulation of wake effects for a single turbineResearch on wake effects for a single turbine focused on a freely developing wake.A full-scale 3D model was constructed for the NREL 5MW reference offshore wind turbine,neglecting the effects of nacelle,tower,and yaw angle.A numerical simulation was conducted for a single-phase wind inflow,and the results of torque calculations were compared with those of the NREL report to verify the reliability of the model.The study focused on the distribution of wake at different downstream positions and the development of wake.The results showed that wake attenuation decreased as the downstream distance increased,and the width of the wake gradually increased.(2)Numerical simulation of wave and wind-wave couplingNumerical simulation of waves served as the basis for wind-wave coupling simulation.The second-order stokes wave was selected as the wave type,and wave parameters for the Donghai 40 sea area were referenced.The numerical wave matched the theoretical wave profile well.A numerical simulation was conducted for a single turbine under wind-wave coupling conditions.The results showed that wind-waves lifted up after a certain distance from the inlet,while the inflow wind speed decreased.In the coupled condition,wake attenuation within a 10D range downstream of the turbine was more severe than that in the wind-only case,whereas beyond 10D,wake recovery was more significant.(3)Numerical simulation of wake interference effectsFor offshore wind turbines,which have relatively dispersed layouts,wake interference between two turbines in series is the most representative form of interference.A 3D full-scale model was constructed for the NREL 5MW wind turbine in a series configuration,with the Xinghua Bay offshore wind farm in Donghai as the study site.The effects of wake interference on turbine output and velocity distribution in the flow field were compared for wind-only and wind-wave coupling conditions.The results showed that wake from inflow wind-waves caused a decrease in power output of downstream turbines,but also resulted in more significant wake recovery.When planning the layout of turbines in offshore wind farms,the effect of wave-induced acceleration on far-field wakes should be taken into account,and turbine spacing can be increased accordingly to improve overall power generation efficiency.