Abstract
The Actuator Disk (AD) model is widely used in Large-Eddy Simulations (LES) to simulate wind turbine wakes because of its computing efficiency. The capability of the AD model in predicting time-average quantities of wind tunnel-scale turbines has been assessed extensively in the literature. However, its capability in predicting wakes of utility-scale wind turbines especially for the coherent flow structures is not clear yet. In this work, we take the time-averaged statistics and Dynamic Mode Decomposition (DMD) modes computed from a well-validated Actuator Surface (AS) model as references to evaluate the capability of the AD model in predicting the wake of a 2.5 MW utility-scale wind turbine for uniform inflow and fully developed turbulent inflow conditions. For the uniform inflow cases, the predictions from the AD model are significantly different from those from the AS model for the time-averaged velocity, and the turbulence kinetic energy until nine rotor diameters (D) downstream of the turbine. For the turbulent inflow cases, on the other hand, the differences in the time-averaged quantities predicted by the AS and AD models are not significant especially at far wake locations. As for DMD modes, significant differences are observed in terms of dominant frequencies and DMD patterns for both inflows. Moreover, the effects of incoming large eddies, bluff body shear layer instability, and hub vortexes on the coherent flow structures are discussed in this paper.
Highlights
Nowadays, large wind farms are constructed to respond to the increasing demand of renewable energy
We evaluate the capability of an actuator disk model in predicting the wake dynamics of a utility-scale wind turbine by comparing its results with those from an actuator surface model
It is found that time-averaged velocity and turbulence kinetic energy computed by the Actuator Disk (AD) model are significantly different from those computed by the Actuator Surface (AS) model until nine turbine rotor diameters downstream for the uniform inflow condition; for fully developed turbulent inflow, the differences between the two models are less significant and agree with each other from seven turbine rotor diameters downstream
Summary
Large wind farms are constructed to respond to the increasing demand of renewable energy. In these wind farms, turbines are installed in cluster to meet the geographical restriction and to reduce the cable and maintenance cost. A need to better understand the wake behavior and its influence on the downwind turbines arises. Understanding turbine wakes in a wind farm is challenging because of its multi-scale nature. The difficulty in accurately modeling the flow around the blade of a real wind turbine blade arises both in wind tunnel experiments (due to scale effect [3]) and in numerical simulations (due to the resolution requirement)
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