Near wake analysis of actuator line method immersed in turbulent flow using large-eddy simulations

Abstract

Abstract. The interaction between wind turbines through their wakes is an important aspect of the conception and operation of a wind farm. Wakes are characterized by an elevated turbulence level and a noticable velocity deficit which causes a decrease in energy output and fatigue on downstream turbines. In order to gain a better understanding of this phenomenon this works uses large-eddy simulations together with an actuator line model and different ambient turbulences imposed as boundary conditions. This is achieved by using the SOWFA framework from NREL (USA) which is first validated against another popular CFD 5 framework for wind energy, EllipSys3D, and then verified against the experimental results from the MEXICO and NEW MEXICO wind tunnel experiments. By using the predicted torque as a global indicator, the optimal width of the distribution kernel for the actuator line is determined for different grid resolutions. Then the rotor is immersed in homogeneous isotropic turbulence and a shear layer turbulence with different turbulence intensities, allowing to determine how far downstream the effect of the distinct blades is discernible. This can be used as an indicator for the extents of the near wake for different flow 10 conditions.

Analytical three‐dimensional wind flow model for real‐time wind farm simulation

“…Wake models are often based on LES studies [11, 27, 31, 34, 58–61], wind tunnel experiments [8–10, 12, 31, 59, 61, 62] or on measurement data from utility‐scale turbines [63–65] to derive simplified analytical models. The most important characteristics of interest are the contour of the wake field, velocity deficit, yaw behaviour, turbulence increase, vortices and meandering [11, 24, 31, 34, 61, 66, 67]. The model proposed by Jiménez et al involves wake deflection depending on the rotor yaw angle, but it also comprises the top‐hat shape [60].…”

“…The National Renewable Energy Laboratory's (NREL) high fidelity Simulator fOr WF Applications (SOWFA) [22], which is based on the OpenFOAM toolbox [23], is widely used to analyse aerodynamic interrelationships under different conditions or as comparison model reference [24][25][26][27][28][29][30][31][32][33][34]. In addition, the Fatigue, Aerodynamics, Structures, and Turbulence (FAST) tool for non-linear aero-hydro-servo-elastic simulation of WT rotors, structural loads and drive train components can be coupled to SOWFA to cover all relevant processes and energy conversions with high detail [35].…”