Turbulence characteristics in a free wake of an actuator disk: comparisons between a rotating and a non-rotating actuator disk in uniform inflow

Abstract

An Actuator Disk (AD) model is implemented in the CFD platform OpenFOAM® with the purpose of studying the characteristics of the turbulent flow in the wake of the rotor of a horizontal-axis wind turbine. This AD model is based on the blade-element theory and it employs airfoil data to calculate the distribution of forces over the disk of a conceptual 5 MW offshore wind turbine. A uniform, non-turbulent flow is used as inflow so the turbulence is only produced in the wake of the AD. Computations are performed using Large-Eddy Simulations (LES) to capture the unsteady fluctuations in the flow. Additionally, a classic Smagorinsky Sub-Grid Scale (SGS) technique is employed to model the unfiltered motions. This new AD implementation makes use of a control system to adjust the rotational velocity of the rotor (below rated power) to the local conditions of the wind flow. The preliminary results show that the wake characteristics are influenced by the force distribution on the disk when compared to the wake produced by a uniformly loaded AD. Also, we observe that the simulated rotor reacts correctly to the introduction of the control system, although operating below the optimal power.