Numerical Simulations of Wind Turbine Wakes
Niels Troldborg
Department of Mechanical Engineering, DTU
Abstract:
The motivation for recent studies of wind turbine wakes are mainly that turbines clustered in wind farms often operates partly or fully in the wake of upstream turbines hence experiences a significantly modified wind field compared to isolated wind turbines.
Wind turbine wakes are in the near region largely characterized by stable vortical structures emanated from the tip and root section of the turbine blades. The near wake interacts with the ambient atmospheric turbulence, which perturbs the helical vortex systems whereby the wake breaks up in a chaotic process resulting in increased turbulence levels inside the wake. Furthermore, large scale behaviour from this interaction is observed as a meandering development of the wake.
Accurate analysis of wake interaction between turbines seeks to characterize the turbulence field inside the wakes prior to impacting downstream turbines in order to predict produced power and fatigue loads. The present analysis is based on CFD modelling using the EllipSys3D flow solver and the Actuator Line technique combined with refined modelling of wind shear and elegant inclusion of ambient turbulence from the Mann turbulence model.
The presentation will introduce the recent advances in numerical modelling of wake using the actuator line technique. The main focus is to study and characterize the turbulence field in the wake of an isolated wind turbine operating in various inflow conditions but also results from respectively two and three interacting wakes are discussed in some details.