Numerical Simulation Of Complex Wake Flows For Wind Farm Based On Actuator Line Model

With the wide application of wind power,more and more wind farms have been set up all over the world.The grouping of turbines in farms introduces a major issue:reducing power production due to wake velocity deficits and high turbulence in wake.Depending on the layout and the wind conditions of a wind farm,the power loss of a downstream turbine can be easily reached 40%in full-wake conditions.Therefore,there is great scientific and engineering value on the numerical study for the characteristics of wake flow in the wind farm,including the aerodynamic loads,dynamic loads of the blades,and the complex wake effects and significant wake interaction.In this thesis,numerical simulations of wake flows for the multiple wind-turbine in the wind farm have been conducted to study the output of aerodynamic load and wake characteristics.The complex wake effects and significant wake interference effects were also under research.Firstly,a numerical validation for the wind farm solver named ALMWindFarmFoam which is one of modules in the FOWT-UALM-SJTU has been carried out compared with the Blind Test 2.The validation including aerodynamic loads,average wake velocity and average turbulent stress indicated that there is enough reliability and accuracy of the ALMWindFramFoam module for wind farm simulation.Secondly,based on two different wind farm layouts,series numerical studies have been carried out and the influences of streamwise and cross-flow separation between the upstream and downstream wind turbine for aerodynamics have been discussed in detail.The results show that the separation in direction of both streamwise and cross-flow between the rotors is significant to the aerodynamic interaction,especially for the downstream wind turbines.In addition,inside the area of five times diameter of the rotor is the strong wake effect district and outside the area is the weak wake effect district.When the downstream wind turbine is fully located in the district of the wake of the upstream wind turbine,there is serious deficit for wind speed and power output.When far away from the strong wake effect district,the recovery for the aerodynamic power of the downstream is obvious and the recovering speed is twice the speed in the strong wake effect district.When the downstream wind turbine is partly located in the district of the wake of the upstream,the turbulence characteristics are also obvious in the wake overlap area with accelerating recovery for the wake speed.The shape of wake shows a distinct asymmetry.Finally,a numerical investigation based on the Lillgrund wind farm layout has been executed to discuss the aerodynamic loads,complex wake effects and significant wake interactions.The investigation indicated that when the wind turbines aligned with in-line model,the minimum power output occurs at the third wind turbine in the downstream.With the recovery of wake speed after the third turbine,the power outputs of downstream turbines gradually increase and finally reach a stable value.Furthermore,when the first wind turbine operates in a rated condition,there is maximum wake speed deficit,greatly lowering the power output of following turbines in the downstream.Moreover,due to the serious wake interaction,there wake flow becomes more unstable and result that the wake speed loss area alternates obviously,which may cause significant fatigue loads on the blades.