Abstract
As part of the Perdigão 2017 campaign, vertical RHI (range-height indicator) scans with long-range pulsed Doppler wind lidars were performed aligned with the main wind direction and a wind turbine (WT) located on a mountain ridge. The measurements are used to not only retrieve flow velocities, but also their variance and - by using the turbulent broadening of the Doppler spectrum - also turbulent kinetic energy (TKE) dissipation rate. The study shows that turbulence in the WT wake is dependent on the turbulence of the inflow, but also on atmospheric stability. In stable atmospheric conditions, wakes could be analyzed up to five rotor diameters downstream (D) and showed the maximum turbulence in the wake at 2-3 D, whereas in unstable conditions, the maximum was found at 2 D and the wake could not be detected further than 3 D. A clear dependency of wake turbulence enhancement on inflow turbulence intensity is found, which levels out to no further enhancement at turbulence intensities of 30%.
Highlights
Amongst the challenges in wind-energy research, turbulence plays an important role for the understanding of inflow conditions [1, 2]
Within a wind turbines (WT) wake, increased levels of turbulence generated by the vortices of the rotor blades can be expected
In this study we quantify this enhancement of atmospheric turbulence up to five rotor diameters downstream through RHI measurements with long-range lidars
Summary
Amongst the challenges in wind-energy research, turbulence plays an important role for the understanding of inflow conditions [1, 2]. Turbulence generated by wind turbines (WT) in their wakes is a feature that is inherent to every wind park and deserves special regards. Wakes, and their interaction with atmospheric flows, have been studied theoretically [3], in simulations [4, 5, 6, 7], and in experiments [8, 9, 10, 11, 12, 13]. Short-range, continuous-wave Doppler wind lidars can provide very detailed measurements of the wake in the near-field of the turbine [14, 15].
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