Comparison of Wind Turbine Wakes in Steady and Turbulent Inflow

Abstract

This paper presents simulation results of wake effects in a wind farm, under both steady and turbulent inflow conditions. Depending on a wind farm’s design, wake interference can cause large power losses and increased turbulence levels. The extent of these wake interference effects depends strongly on the atmospheric inflow conditions. The objective of the present study is to employ several modeling methods to reach an improved understanding of wake effects and to use this information to better optimize a farm’s layout. The methods used in order of low to high complexity are: a blade element model with freevortex wake approach for inflow (UWake), an actuator disk based Reynolds-averaged Navier-Stokes (RANS) Computational Fluid Dynamics (CFD) method (DiskFloW) and a full blade RANS CFD code (HELIOS) that utilizes adaptive mesh refinement (AMR). The methods are collectively employed to model wind turbines at the Sexbierum wind farm, which allows for comparisons to experimental data and also for cross comparisons between the models. Single turbine wake deficits are modeled using both steady and turbulent inflow. Inflow turbulence is introduced using data from a precursor large eddy simulation (LES) of a neutral atmospheric boundary layer (ABL). A two turbine exact row case is also modeled to investigate the dependence of the power deficit at the downstream turbine on inflow conditions. The differences in the diffusion of the wake with and without turbulent inflow are presented, and the limitations of each method are discussed.