Abstract
Abstract. A simple wind-speed-independent actuator disk control method is proposed that can be applied to speed up annual energy production calculations of wind farms using Reynolds-averaged Navier–Stokes simulations. The new control method allows the user to simulate the effect of different wind speeds in one simulation by scaling a calibrated thrust coefficient curve, while keeping the inflow constant. Since the global flow is not changed, only the local flow around the actuator disks need be recalculated from a previous converged result, which reduces the number of required iterations and computational effort by a factor of about 2–3.
Highlights
Wind turbine wakes cause energy losses in wind farms (Barthelmie et al, 2007) and increase blade fatigue loads
Reynoldsaveraged Navier–Stokes (RANS) is a relatively fast, yet highfidelity, computational fluid dynamics (CFD) method that can be used for this purpose, it is still computationally expensive compared to the traditional engineering approaches
The annual energy production (AEP) of the 5 × 5 NREL-5MW wind farm is calculated with RANS-actuator disks (ADs) simulation(s) using 22 wind speeds between 4 and 25 m s−1 and 16 wind directions between 270 and 315◦ using the symmetry of the wind farm layout
Summary
Wind turbine wakes cause energy losses in wind farms (Barthelmie et al, 2007) and increase blade fatigue loads. The Reynolds number of the RANS-AD simulations, based on a rotor diameter of 100 m, is on the order of 107–108 for a wind speed range of 4–25 m s−1. For these large Reynolds numbers, RANS simulations of a single AD are Reynolds number independent. The Reynolds number independence only holds if the inflow scales by a velocity scale, i.e. the friction velocity This is true for atmospheric surface layer profiles following Monin–Obukhov similarity theory, where the turbulence length scale is invariant of the wind speed. For RANS-AD simulations of wind farms, the thrust coefficient varies within the wind farm, which means that one still needs to simulate multiple wind speed cases despite the Reynolds number independence of the flow
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