Simulation of wake effects of windfarms using an Actuator Disk implementation

Abstract

AbstractWind turbines extract energy from the approaching flow field resulting in reduced wind speeds, increased turbulence and a wake downstream of the wind turbine. Wakes extending up to 20 km downstream of a windfarm are reported [1]. In [2] a multi‐scale numerical method is proposed that addresses length scales of the boundary layer, windfarm and meso‐scale. As a step towards full realization of the multi scale approach the implementation of an Actuator Disk (AD) model into OpenFOAM including a proper atmospheric boundary layer (ABL) is presented. For a meso‐scale area of open sea, the standard ABL conditions of OpenFOAM can not be used. The pre implemented ABL boundary condition for OpenFOAM is restricted to roughness lengths greater than 0.001 m. The boundary condition are modified in order to achieve adequate homogeneous flow properties throughout the considered domain enabling almost constant velocity profiles. A new AD class is implemented in OpenFOAM to establish an arbitrary number and location of windturbines. The class uses the standard k‐ϵ turbulence model. The wake effect of windfarms composed of windturbines with different heights and different lateral spacing is investigated. Specifically the windfarm Trianel Borkum in the North Sea of Germany is simulated. Within this work wakes extending up to 20 km in length could be observed, suggesting to study the ABL‐windfarm interaction in more detail. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)