A Comparative Analysis on the Response of a Wind-Turbine Model to Atmospheric and Terrain Effects

Abstract

In a series of wind-tunnel experiments conducted at the St. Anthony Falls Laboratory, a wind-turbine model was exposed to three different thermal regimes (neutral, weakly stable and weakly convective flows) in three simple arrangements relevant to wind-farm applications: single turbine in the boundary-layer, aligned turbine-turbine, and an upwind three-dimensional sinusoidal hill aligned with the turbine. Results focus on the spatial evolution of large-scale motions developing over the different thermal and topographic boundary conditions, and on their influence on the mean and fluctuating angular velocity of the turbine rotor. As compared to the single turbine case, both the upwind hill and turbine caused a reduction in the mean angular velocity regardless of the thermal regime; the turbine angular velocity fluctuations always decreased with a turbine upwind, which depleted the energy of the large structures of the flow; however such fluctuations decreased (increased) under stably stratified (convective) conditions when the hill was present. Pre-multiplied spectra of the rotor angular velocity and two-point correlation contours of the streamwise velocity component confirmed a non-trivial link between thermal stratification and terrain complexity. It is inferred that the thermal effects occurring in the three different boundary-layer regimes modulate the spanwise motion of the hill wake and define whether the hill shelters or exposes the turbine to enhanced large-scale energetic motions.

The spectral signature of wind turbine wake meandering: A wind tunnel and field‐scale study

“…While the laboratory inflow conditions were observed to provide a genuine, scaled representation of the atmospheric surface layer at the Eolos site, 14,33,52 the model and utility-scale turbine performances are significantly different. In particular, the wake deficit in the miniature turbine models is due to a relatively large drag as opposed to an efficient energy harnessing (see discussion of Howard et al 52 ).…”

“…While the laboratory inflow conditions were observed to provide a genuine, scaled representation of the atmospheric surface layer at the Eolos site, 14,33,52 the model and utility-scale turbine performances are significantly different. In particular, the wake deficit in the miniature turbine models is due to a relatively large drag as opposed to an efficient energy harnessing (see discussion of Howard et al 52 ). It is thus speculated here that the wake energy excess is primarily associated with the tip vortex structure and annular shear layer delimiting the rotor wake: a highperforming field-scale turbine with optimal blade design would ensure high shear, large deficit, and a strong meandering wake (deployments 2, 3, and 4); the same turbine in a derated state would have a weaker tip vortex structure, shear layer, mean deficit, and meandering wake (deployment 5).…”

“…2018;21:715-731. https://doi.org/10.1002/we.2189 Model turbine wake measurements were collected in the St Anthony Falls Laboratory closed-loop atmospheric boundary layer wind tunnel for comparison with field-scale results. The tunnel test section length is 16 m, and the cross section is 1.7m × 1.7 m. A turbulence trip at the test section leading edge develops a boundary layer under zero pressure gradient conditions, keeping the turbine hub height z hub in the bottom 25% of the boundary layer height δ ≈ 0.6 m (see other works14,31,52,56 for example boundary layer and wake profiles). The free-stream and floor surface temperatures can be controlled to simulate different thermal stability conditions.…”

“…Neutral thermal conditions were used for the experiments in this study. The model wind turbine used in the wind tunnel experiments has a 3-blade GWS/EP-5030×3 rotor with a 0.128-m rotor diameter and 0.104-m hub height 33,50,52,56. The optimal tip-speed ratio of the model is λ≈ 3.2.…”

A wind‐tunnel study of the wake development behind wind turbines over sinusoidal hills

“…When compared to an undisturbed case over flat terrain, a wind turbine placed behind one of the hill configurations in Figure would feature a loss in power due to the reduced inflow velocity it would perceive. Higher turbulence levels can also be expected behind hills, something that increases the fatigue loads on the turbine but also reduces the extent of the near‐wake region and promotes the turbine wake recovery . The faster wake recovery is beneficial in cases where the wakes behind multiple wind turbines interact regardless of the local terrain topography.…”