Wind Turbine Wake Characterization with Nacelle-Mounted Wind Lidars for Analytical Wake Model Validation

Abstract

This study presents the setup, methodology and results from a measurement campaign dedicated to the characterization of full-scale wind turbine wakes under different inflow conditions. The measurements have been obtained from two pulsed scanning Doppler lidars mounted on the nacelle of a 2.5 MW wind turbine. The first lidar is upstream oriented and dedicated to the characterization of the inflow with a variety of scanning patterns, while the second one is downstream oriented and performs horizontal planar scans of the wake. The calculated velocity deficit profiles exhibit self-similarity in the far wake region and they can be fitted accurately to Gaussian functions. This allows for the study of the growth rate of the wake width and the recovery of the wind speed, as well as the extent of the near-wake region. The results show that a higher incoming turbulence intensity enhances the entrainment and flow mixing in the wake region, resulting in a shorter near-wake length, a faster growth rate of the wake width and a faster recovery of the velocity deficit. The relationships obtained are compared to analytical models for wind turbine wakes and allow to correct the parameters prescribed until now, which were obtained from wind-tunnel measurements and large-eddy simulations (LES), with new, more accurate values directly derived from full-scale experiments.

Theoretical Modeling of Vertical-Axis Wind Turbine Wakes

“…Note that assuming an elliptical shape for the wake allows the model to take into account the effect of turbine aspect ratio. As previously shown [22,31,[34][35][36][37][38][39][40], σ z and σ y are varying quasi-linearly with downwind distance in turbulent inflow as…”

“…As stated before, it would be more convenient and practical to specify only one input parameter (i.e., k w for the top-hat and k * for the Gaussian-type wake models) to determine the wind velocity downstream of the turbine. Here, the wake expansion ratios in the top-hat and Gaussian-type wake models are estimated from the following expressions suggested for the wake development in turbulent regimes without any further tuning: k w = 0.4I u [44] and k * = 0.35I u [39]. Figure 1 illustrates the spatial distribution of the time-averaged velocity in the streamwise direction and in the central vertical and lateral planes, obtained from the LES, for Cases (1)(2)(3).…”

An Analytical Model for the Effect of Vertical Wind Veer on Wind Turbine Wakes

“…Similar to the previous studies [15,[42][43][44]47,48], it is assumed that, under turbulent inflow conditions, σ y and σ z are expanded approximately linearly with downwind distance as…”

Cluster wakes impact on a far-distant offshore wind farm's power

“…Wake measurements were mainly performed using the remote-sensing technique Doppler lidar (e.g. Aitken et al, 2014;Trabucchi et al, 2017;Bodini et al, 2017;Fuertes et al, 2018;Beck and Kühn, 2019), power analysis on the basis of SCADA data (e.g. Barthelmie and Jensen, 2010) or Doppler radar (e.g.…”