Abstract
In this study, the wake behind a wind turbine located on an escarpment is investigated using particle-image velocimetry in a wind tunnel. Five different escarpment models are used, which vary in the windward side shape from forward facing steps (FFS) with different curvatures at the leading-edge to sinusoidal ramp shapes with varying slopes. The difference in the base flow (flow without the turbine) resulting from the change in the geometry of the escarpment leads to significant differences in the average and dynamic characteristics of the turbine wake. The relatively high level of turbulence intensity in the base flow induced by the FFS escarpments leads to a faster wake recovery accompanied by higher turbulence kinetic energy, compared with the ramp-shaped ones. The self-similar behavior of the velocity deficit profiles in the far wake is confirmed for all the cases; unlike turbine wakes over flat terrain, the wake growth rate is found to be larger in the vertical direction than in the lateral direction. Meandering of the wake is observed to be higher on the FFS escarpment with an upward wake trajectory, compared to the ramp-shaped one. Finally, an analytical model is assessed to predict the wake velocity deficit of the turbine.
Highlights
The global wind energy capacity has exceeded 600 GW in the year 2019 [1]
Onshore wind energy has grown tremendously over the last two decades, with wind farms often located in complex terrain
We have characterized the wake generated by a single wind turbine sited on different escarpments using stereo-PIV measurements
Summary
The global wind energy capacity has exceeded 600 GW in the year 2019 [1]. Onshore wind energy, in particular, has experienced a tremendous growth since the dawn of this century, accounting for about 96% of the total installed wind energy capacity. Tian et al [50] did an experimental investigation of a wind farm sited on a Gaussian hill to assess the interaction between the turbine wakes and the topography They showed that the presence of the hill affects the power performance of the turbines and influences the wake of the turbines. Dar et al [59] extended the work of Berg et al [60] to study the wakes under different levels of terrain complexity and turbine locations using large-eddy simulation. Dar & Porte-Agel [68] performed a three-dimensional characterization of the wake behind a turbine sited on two different escarpments using tomographic particle-image velocimetry They showed that the shape of the escarpment has an influence on the mean, as well as the dynamic characteristics of the wake.
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