Effects of an escarpment on flow parameters of relevance to wind turbines

et al. 2018

Preprint

Self Cite

Abstract. When conducting meso-micro scale coupled atmospheric simulations, it is crucial to ensure an adequate treatment of gray zone or terra incognita resolutions in which a large portion of the kinetic energy is naturally produced by the momentum balance equations in the model, while the remaining part still needs to be parameterized. In this work, we conduct three multiday, real case, full-physics atmospheric simulations that are fully coupled from the meso to the micro scale and in which the only difference is the treatment of boundary layer physics at the gray zone domain. One simulation uses a well-established 5 parameterization, another uses its scale-aware version previously modified to accommodate gray zone resolutions, and a final one uses no parameterization at all and assumes that the gray zone domain can be run in large-eddy simulation (LES) mode.The simulated fields are cross-compared, and further compared to measurements collected during the Prince Edward Island Wind Energy Experiment. Use of LES in the gray zone domain influences the flow fields in a manner that is robust to temporal averaging. The best predictions of vertical wind shear were found for the simulations in which the gray zone is parameterized, 10 and the inclusion of a micro scale nest run in LES mode within the gray zone domains increased the model errors by producing overly homogeneous flow fields. The parameterized simulations also produced better agreement in terms of kinetic energy spectra at the two innermost simulation domains. In the gray zone domain, the energy decays as f −3 throughout most of the spectral range considered. In the micro scale domain, the same is only seen in the low-frequency end of the gray zone spectral range. In the high-frequency end, the energy decay follows a f −1 slope. Outside the gray zone spectral range, the micro scale 15 simulated spectra follow the expected f −5/3 slope and produce good agreement with measurements.

Section: Horizontal Wind Speedmentioning

confidence: 79%

Section: Study Domain and Measurementsmentioning

confidence: 99%

See 1 more Smart Citation

Analysis of Different Gray Zone Treatments in WRF-LES Real Case Simulations

Doubrawa

Montornès²,

et al. 2018

Preprint

Self Cite

“…The observational dataset used in this work was collected during the Prince Edward Island Wind Energy Experiment at the Wind Energy Institute of Canada [22]. We focus on single wake measurements during a 22-h period (26 May 2015 13:00 UTC-27 May 2015 11:00 UTC) downstream of a 2-MW DeWind D9.2 turbine with a hub height (z H , the H subscript indicates turbine hub throughout the manuscript) of 80 m and a rotor diameter (D) of 93 m. The wake characterization is based on the metrics proposed by [21], which are defined for two-dimensional planes of data in the cross-stream (x) and vertical (z) directions.…”

Section: Field Scansmentioning

confidence: 99%

“…The uncertainty in the measurements and resulting wake characterization is estimated by placing an imaginary scanning LiDAR at the bottom of a wind turbine in an LES of a single wake under slightly stable conditions, which is also true of the measurements [22]. From here onwards, the term "synthetic scan" is used to refer to data that are obtained by sampling numerical simulation output according to the spatial and temporal coordinates of each point in the xz-planes obtained from the field measurements.…”

Section: Synthetic Scansmentioning

confidence: 99%

Wind Turbine Wake Characterization from Temporally Disjunct 3-D Measurements

Doubrawa

Wang³

et al. 2016

Remote Sensing

Scanning LiDARs can be used to obtain three-dimensional wind measurements in and beyond the atmospheric surface layer. In this work, metrics characterizing wind turbine wakes are derived from LiDAR observations and from large-eddy simulation (LES) data, which are used to recreate the LiDAR scanning geometry. The metrics are calculated for two-dimensional planes in the vertical and cross-stream directions at discrete distances downstream of a turbine under single-wake conditions. The simulation data are used to estimate the uncertainty when mean wake characteristics are quantified from scanning LiDAR measurements, which are temporally disjunct due to the time that the instrument takes to probe a large volume of air. Based on LES output, we determine that wind speeds sampled with the synthetic LiDAR are within 10% of the actual mean values and that the disjunct nature of the scan does not compromise the spatial variation of wind speeds within the planes. We propose scanning geometry density and coverage indices, which quantify the spatial distribution of the sampled points in the area of interest and are valuable to design LiDAR measurement campaigns for wake characterization. We find that scanning geometry coverage is important for estimates of the wake center, orientation and length scales, while density is more important when seeking to characterize the velocity deficit distribution.

The impact of wind direction yaw angle on cliff flows

Pryor

2018

Wind Energy

Self Cite

The behavior of flow close to a cliff at heights relevant to wind turbines is explored using observations and simulations from a field experiment conducted at the Wind Energy Institute of Canada Prince Edward Island field site. There are 4 wind turbines located approximately 100 m from a 12 m high cliff and a fifth turbine located 500 m inland. During the field experiment, ongoing mast‐based observations were supplemented with additional sonic anemometers and Doppler lidars. Consistent with wind tunnel measurements and previous model simulations, a small speedup in the flow (~3‐5%) at the turbine hub‐height (of 80 m) is observed when the flow is perpendicular to the cliff. The objective here is to determine the degree to which the magnitude of the speedup, or horizontal distance over which it is manifest, changes as the flow deviates from the perpendicular impingement angle (ie, for nonzero yaw angles). Results indicate that the zone of deceleration upwind of the cliff and the downwind acceleration zone are maintained with flow ±25° to the perpendicular. Further, there is little change in the relative magnitude of either the wind speed or the turbulence intensity with modest deviations from perpendicular flow. However, as the angle from the perpendicular increases (ie, flow becomes increasingly parallel to the coast), the impact on wind speed and turbulence intensity decreases and is manifest over narrow and spatially less coherent regions.