Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session A27: Energy: Wind and Hydraulic PowerEnergy
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Chair: Xiaolei Yang, Stony Brook University Room: 709 |
Sunday, November 19, 2017 8:00AM - 8:13AM |
A27.00001: Particle image and acoustic Doppler velocimetry analysis of a cross-flow turbine wake Benjamin Strom, Steven Brunton, Brian Polagye Cross-flow turbines have advantageous properties for converting kinetic energy in wind and water currents to rotational mechanical energy and subsequently electrical power. A thorough understanding of cross-flow turbine wakes aids understanding of rotor flow physics, assists geometric array design, and informs control strategies for individual turbines in arrays. In this work, the wake physics of a scale model cross-flow turbine are investigated experimentally. Three-component velocity measurements are taken downstream of a two-bladed turbine in a recirculating water channel. Time-resolved stereoscopic particle image and acoustic Doppler velocimetry are compared for planes normal to and distributed along the turbine rotational axis. Wake features are described using proper orthogonal decomposition, dynamic mode decomposition, and the finite-time Lyapunov exponent. Consequences for downstream turbine placement are discussed in conjunction with two-turbine array experiments.~ [Preview Abstract] |
Sunday, November 19, 2017 8:13AM - 8:26AM |
A27.00002: Towards a Wind Turbine Wake Reduced-Order Model Nicholas Hamilton, Bianca Viggiano, Marc Calaf, Murat Tutkun, Raúl Bayoán Cal A reduced-order model for a wind turbine wake is sought for prediction and control. Basis functions from the proper orthogonal decomposition (POD) represent the spatially coherent turbulence structures in the wake; eigenvalues delineate the turbulence kinetic energy associated with each mode. Back-projecting the POD modes onto the velocity snapshots produces coefficients that express the amplitude of each mode in time. A reduced-order model of the wind turbine wake (wakeROM) is defined through a series of polynomial parameters that quantify mode interaction and the evolution of each mode coefficient. Tikhonov regularization is employed to recalibrate the dynamical system, reducing error in the modeled mode coefficients and adding stability to the system. The wakeROM is periodically reinitialized by relating the incoming turbulent velocity to the POD mode coefficients. A high-level view of the wakeROM provides as a platform to discuss promising research direction, alternate processes that will enhance stability, and portability to control methods. [Preview Abstract] |
Sunday, November 19, 2017 8:26AM - 8:39AM |
A27.00003: ABSTRACT WITHDRAWN |
Sunday, November 19, 2017 8:39AM - 8:52AM |
A27.00004: Frequency modulation for a wind turbine blade-mounted ultrasonic bat deterrent Daniel Carlson, Zara Dowling, Paul Sievert, Yahya Modarres-Sadeghi Progress on developing a bat deterrent device for placement on the rotating blades of a wind turbine is presented. The mechanisms by which bat larynxes generate ultrasound is studied and reproduced experimentally. In previous iterations, flow-induced oscillations have been used to generate ultrasonic frequencies within the 20-70 kHz range: a range which laboratory studies have shown can deter bats from an area. However, the present work considers mechanisms which result in frequency modulation within the higher harmonics, an acoustic signal closer to what bats naturally avoid. Results discussed include the effects of spanwise tension on the flapwise oscillation of a pseudo larynx in flow, and how shifting the flapwise natural frequency allows frequency modulation. The net effect is a device effective within the range of wind speeds encountered along the length of a rotating wind turbine blade. \newline [Preview Abstract] |
Sunday, November 19, 2017 8:52AM - 9:05AM |
A27.00005: Vortex-Induced Vibration of an Airfoil Used in Vertical-Axis Wind Turbines Bridget Benner, Daniel Carlson, Banafsheh Seyed-Aghazadeh, Yahya Modarres-Sadeghi In Vertical-axis wind turbines (VAWTs), when the blades are placed at high angles of attack with respect to the incoming flow, they could experience flow-induced oscillations. A series of experiments in a re-circulating water tunnel was conducted to study the possible Vortex-Induced Vibration (VIV) of a fully-submerged, flexibly-mounted NACA 0021 airfoil, which is used in some designs of VAWTs. The airfoil was free to oscillate in the crossflow direction, and the tests were conducted in a Reynolds number range of 600\textless \textit{Re}\textless 13,300 and reduced velocity range of 0.6\textless $U*$\textless 13. The amplitudes of oscillations and flow forces acting on the airfoil were measured at various angles of attack, $\alpha $, in the range of 0\textless $\alpha $\textless 90. The airfoil was observed to oscillate in the range of 60\textless $\alpha $\textless 90, where $\alpha =$90 exhibited the widest lock-in range (1.67\textless $U*$\textless 11.74) and the largest peak amplitude ($A*=$1.93 at $U*=$5.7). For all cases where oscillations were observed, the oscillation frequency remained close to the structure's natural frequency, defining a lock-in range. Flow visualization tests were also conducted to study the changes in the vortex shedding patterns. [Preview Abstract] |
Sunday, November 19, 2017 9:05AM - 9:18AM |
A27.00006: Prediction and control of coupled-mode flutter in future wind turbine blades Yahya Modarres-Sadeghi, Todd Currier, Luca Caracoglia, Matthew Lackner, Christopher Hollot Coupled-mode flutter can be observed in future offshore wind turbine blades. We have shown this fact by considering various candidate blade designs, in all of which the blade's first torsional mode couples with one of its flapwise modes, resulting in coupled-mode flutter. We have shown how the ratio of these two natural frequencies can result in blades with a critical flutter speed even lower than their rated speed, especially for blades with low torsional natural frequencies. We have also shown how the stochastic nature of the system parameters (as an example, due to uncertainties in the manufacturing process) can significantly influence the onset of instability. We have proposed techniques to predict the onset of these instabilities and the resulting limit-cycle response, and strategies to control them, by either postponing the onset of instability, or lowering the magnitude of the limit-cycle response. \newline [Preview Abstract] |
Sunday, November 19, 2017 9:18AM - 9:31AM |
A27.00007: Wake characteristics of wind turbines in utility-scale wind farms Xiaolei Yang, Daniel Foti, Fotis Sotiropoulos The dynamics of turbine wakes is affected by turbine operating conditions, ambient atmospheric turbulent flows, and wakes from upwind turbines. Investigations of the wake from a single turbine have been extensively carried out in the literature. Studies on the wake dynamics in utility-scale wind farms are relatively limited. In this work, we employ large-eddy simulation with an actuator surface or actuator line model for turbine blades to investigate the wake dynamics in utility-scale wind farms. Simulations of three wind farms, i.e., the Horns Rev wind farm in Denmark, Pleasant Valley wind farm in Minnesota, and the Vantage wind farm in Washington are carried out. The computed power shows a good agreement with measurements. Analysis of the wake dynamics in the three wind farms is underway and will be presented in the conference. [Preview Abstract] |
Sunday, November 19, 2017 9:31AM - 9:44AM |
A27.00008: Appraisal of ALM predictions of turbulent wake features Benedetto Rocchio, Lorenzo Cilurzo, Umberto Ciri, Maria Vittoria Salvetti, Stefano Leonardi Wind turbine blades create a turbulent wake that may persist far downstream, with significant implications on wind farm design and on its power production. The numerical representation of the real blade geometry would lead to simulations beyond the present computational resources. We focus our attention on the Actuator Line Model (ALM), in which the blade is replaced by a rotating line divided into finite segments with representative aerodynamic coefficients. The total aerodynamic force is projected along the computational axis and, to avoid numerical instabilities, it is distributed among the nearest grid points by using a Gaussian regularization kernel. The standard deviation of this kernel is a fundamental parameter that strongly affects the characteristics of the wake. We compare here the wake features obtained in direct numerical simulations of the flow around 2D bodies (a flat plate and an airfoil) modeled using the Immersed Boundary Method with the results of simulations in which the body is modeled by ALM. In particular, we investigate whether the ALM is able to reproduce the mean velocity field and the turbulent kinetic energy in the wake for the considered bodies at low and high angles of attack and how this depends on the choice of the ALM kernel. [Preview Abstract] |
Sunday, November 19, 2017 9:44AM - 9:57AM |
A27.00009: Effect of seabed roughness on tidal current turbines Vikrant Gupta, Minping Wan Tidal current turbines are shown to have potential to generate clean energy for a negligible environmental impact. These devices, however, operate in high to moderate current regions where the flow is highly turbulent. It has been shown in flume tank experiments at IFREMER in Boulogne-Sur-Mer (France) and NAFL in the University of Minnesota (US) that the level of turbulence and boundary layer profile affect a turbine’s power output and wake characteristics. A major factor that determines these marine flow characteristics is the seabed roughness. Experiments, however, cannot simulate the high Reynolds number conditions of real marine flows. For that, we rely on numerical simulations. High accuracy numerical methods, such as DNS, of wall-bounded flows are very expensive, where the number of grid-points needed to resolve the flow varies as $(Re)^{9/4}$ (where $Re$ is the flow Reynolds number). While numerically affordable RANS methods compromise on accuracy. Wall-modelled LES methods, which provide both accuracy and affordability, have been improved tremendously in the recent years. We discuss the application of such numerical methods for studying the effect of seabed roughness on marine flow features and their impact on turbine power output and wake characteristics. [Preview Abstract] |
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