Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session E2: Wind Turbines: Field Applications |
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Chair: Jiarong Hong, University of Minnesota Room: A106 |
Sunday, November 20, 2016 5:37PM - 5:50PM |
E2.00001: Wind turbine wake meandering at the laboratory and field scales Michael Heisel, Mirko Musa, Jiarong Hong, Michele Guala Flow measurements were collected in the wake of the utility-scale (2.5MW) Eolos wind turbine using a ground-based light detection and ranging (LiDAR) wind profiler to identify the characteristics of wake meandering at the field scale. The investigation seeks to establish the influence of scale and atmospheric turbulence on wake meandering, which has been observed to leave a strong spectral signature on laboratory measurements in wind tunnel and channel flows. The experimental data include multiple test periods at various downstream distances within the turbine wake. Inflow conditions were assessed using a meteorological tower equipped with sonic anemometers. Additionally, an experiment was conducted in the Saint Anthony Falls Laboratory atmospheric boundary layer wind tunnel to provide a direct comparison for the utility-scale results and to reaffirm the findings of previous laboratory-scale investigations. Estimates of the wake and inflow one-dimensional velocity spectra were compared to determine whether wake meandering characteristics are present at both scales. An empirical correction to the velocity spectra of the LiDAR and a few options to extract a more local velocity signal are discussed to compensate for the inherent limitations of LiDAR in capturing turbulent fluctuations. [Preview Abstract] |
Sunday, November 20, 2016 5:50PM - 6:03PM |
E2.00002: Investigating coherent vortex structures in the near wake of a utility-scale wind turbine using flow visualization with natural snowfalls Teja Dasari, Jiarong Hong Flow visualization techniques using natural snowfall have been shown as an effective tool to probe coherent flow structures around utility-scale wind turbines (Hong et al. \textit{Nature Comm.} 2014). Here we present a follow-up study using the data collected during multiple deployments from 2014 to 2016 around the 2.5 MW turbine at EOLOS wind energy research station. The data include flow visualization from different perspectives in the near wake of the turbine. Coherent wake structures, including blade tip vortex, trailing vortex sheet, nacelle-generated structures, and tower vortex characterized by the snow voids, are correlated with atmospheric conditions (e.g. turbulence intensity), turbine operational conditions (e.g. power and tip-speed ratio) as well as turbine response (e.g. tower and blade strain). Physical factors and processes that affect the features and the behaviors of tip vortices including their void size and shape, their stability (e.g. meandering and intermittent appearance) and vortex interaction (e.g. vortex merging and leapfrogging) are analyzed. In particular, a strong influence of the tower on tip-vortex structures is demonstrated through simultaneous comparison of vortex voids at elevations below and above the height of nacelle and the plan view visualization. [Preview Abstract] |
Sunday, November 20, 2016 6:03PM - 6:16PM |
E2.00003: Drone Based Experimental Investigation of Wind Turbine Wake Evolution Dr. Balaji Subramanian, Dr. Ndaona Chokani, Prof. Dr. Reza Abhari The characteristics of the wake downstream of a wind turbine has an important bearing on the optimized micrositing of wind turbines in a given land area, as well as on the loads seen by downstream turbines. We use a novel measurement system to~measure the flow field upstream and in the wake of a full-scale wind turbine. The system consists of a fast response aerodynamic probe, mounted on an autonomous drone that is equipped with a suite of sensors. These measurements detail, for the first time at full-scale Reynolds number conditions, the evolution and breakdown of tip vortices that~are characteristic of the near wake, as well as the turbulent mixing and entrainment of more energised flow, which are distinctive in the far wake. A short-time Fourier transform (STFT) analysis method is used to~derive time-localized TKE along the drone's trajectory. Detailed upstream and wake measurements are needed to understand the flow behavior, as it helps in developing and validating simplified wake models that~can approximate the wake qualities. Comparisons of these measurements to recently developed wake prediction models highlights how these measurements can support further model development. [Preview Abstract] |
Sunday, November 20, 2016 6:16PM - 6:29PM |
E2.00004: Analysis of near-surface relative humidity in a wind turbine array boundary layer using an instrumented unmanned aerial system and large-eddy simulation Kevin Adkins, Oumnia Elfajri, Adrian Sescu Simulation and modeling have shown that wind farms have an impact on the near-surface atmospheric boundary layer (ABL) as turbulent wakes generated by the turbines enhance vertical mixing. These changes alter downstream atmospheric properties. With a large portion of wind farms hosted within an agricultural context, changes to the environment can potentially have secondary impacts such as to the productivity of crops. With the exception of a few observational data sets that focus on the impact to near-surface temperature, little to no observational evidence exists. These few studies also lack high spatial resolution due to their use of a limited number of meteorological towers or remote sensing techniques. This study utilizes an instrumented small unmanned aerial system (sUAS) to gather in-situ field measurements from two Midwest wind farms, focusing on the impact that large utility-scale wind turbines have on relative humidity. Results are also compared to numerical experiments conducted using large eddy simulation (LES). Wind turbines are found to differentially alter the relative humidity in the downstream, spanwise and vertical directions under a variety of atmospheric stability conditions. [Preview Abstract] |
Sunday, November 20, 2016 6:29PM - 6:42PM |
E2.00005: Proactive monitoring of an onshore wind farm through lidar measurements, SCADA data and a data-driven RANS solver Giacomo Valerio Iungo, Simone Camarri, Umberto Ciri, Said El-Asha, Stefano Leonardi, Mario A Rotea, Vignesh Santhanagopalan, Francesco Viola, Lu Zhan Site conditions, such as topography and local climate, as well as wind farm layout strongly affect performance of a wind power plant. Therefore, predictions of wake interactions and their effects on power production still remain a great challenge in wind energy. For this study, an onshore wind turbine array was monitored through lidar measurements, SCADA and met-tower data. Power losses due to wake interactions were estimated to be approximately 4{\%} and 2{\%} of the total power production under stable and convective conditions, respectively. This dataset was then leveraged for the calibration of a data driven RANS (DDRANS) solver, which is a compelling tool for prediction of wind turbine wakes and power production. DDRANS is characterized by a computational cost as low as that for engineering wake models, and adequate accuracy achieved through data-driven tuning of the turbulence closure model. DDRANS is based on a parabolic formulation, axisymmetry and boundary layer approximations, which allow achieving low computational costs. The turbulence closure model consists in a mixing length model, which is optimally calibrated with the experimental dataset. Assessment of DDRANS is then performed through lidar and SCADA data for different atmospheric conditions. [Preview Abstract] |
Sunday, November 20, 2016 6:42PM - 6:55PM |
E2.00006: A Biomimetic Ultrasonic Whistle for Use as a Bat Deterrent on Wind Turbines Paul Sievert, Banafsheh Seyed-Aghazadeh, Daniel Carlson, Zara Dowling, Yahya Modarres-Sadeghi As wind energy continues to gain worldwide prominence, more and more turbines are detrimentally influencing bat colonies. In 2012 alone, an estimated 600,000 bats were killed by wind turbines in the United States. Bats show a tendency to fly towards turbines. The objective of this work is to deter bats from the proximity of the swept area of operational wind turbine blades. Established field studies have shown that bats avoid broadband ultrasonic noise on the same frequency spectrum as their echolocation chirps. A biomimetic ultrasonic pulse generator for use as a bat deterrent on wind turbines is designed and studied experimentally. This device, which works based on the fundamentals of flow-induced oscillations of a flexible sheet is a whistle-like device inspired by a bat larynx, mechanically powered via air flow on a wind turbine blade. Current device prototypes have proven robust at producing ultrasound across the 20 - 70 kHz range for flow inlet velocities of 4 -- 14 m/s. Ultimately, a deterrent as described here could provide a reliable, cost-effective means of alerting bats to the presence of moving turbine blades, reducing bat mortality at wind facilities, and reducing regulatory uncertainty for wind facility developers. [Preview Abstract] |
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