Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session M31: Wind Energy II |
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Chair: Raul Cal, Portland State University Room: 33B |
Tuesday, November 20, 2012 8:00AM - 8:13AM |
M31.00001: Spatial characterization of the turbulent structure of a model wind turbine: high speed PIV measurements Jian Sheng, Leonardo Chamorro, Seung-Jae Lee, Roger Arndt, Fotis Sotiropoulos Wind turbine wakes are complex flow structures that are modulated by the wind turbines and the characteristics of the approach flow, among others. Determining and quantifying the dominating processes that modulate their behavior is essential to improve wind farm design. High speed Particle Image Velocimetry was used to characterize the temporal and spatial features of a model wind turbine wake in their axis of symmetry in the near and far wake field. The model turbine was placed in a boundary layer flow developed in a wind tunnel under neutrally stratified conditions. The high speed measurements allowed us to determine the evolution of a range of coherent structures and their interactions with the surrounding flow. Multi-correlations and spectra as well as the spatial distribution of turbulence quantities provide relevant information on the key turbulent mechanisms that modulate a turbine wake and regulate turbulent transport. [Preview Abstract] |
Tuesday, November 20, 2012 8:13AM - 8:26AM |
M31.00002: Turbulence effects on a full-scale 2.5 MW horizontal axis wind turbine Leonardo Chamorro, Seung-Jae Lee, David Olsen, Chris Milliren, Jeff Marr, Roger Arndt, Fotis Sotiropoulos Power fluctuations and fatigue loads are among the most significant problems that wind turbines face throughout their lifetime. Turbulence is the common driving mechanism that triggers instabilities on these quantities. We investigate the complex response of a full-scale 2.5 MW wind turbine under nearly neutral thermal stratification. The study is performed in the EOLOS Wind Energy Research Field Station of the University of Minnesota. An instrumented 130 meter meteorological tower located upstream of a Clipper Liberty C96 wind turbine is used to characterize the turbulent flow and atmospheric conditions right upstream of the wind turbine. High resolution and synchronous measurements of the wind velocity, turbine power and strain at the tower foundation are used to determine the scale-to-scale interaction between flow and the wind turbine. The structure of the fluctuating turbine power and instantaneous stresses are studied in detail. Important insights about the role of turbulent and coherent motions as well as strong intermittent gusts will be discussed. [Preview Abstract] |
Tuesday, November 20, 2012 8:26AM - 8:39AM |
M31.00003: A wind tunnel study on the effects of complex topography on wind turbine performance Kevin Howard, Stephen Hu, Leonardo Chamorro, Michele Guala A set of wind tunnel experiments were conducted to study the response of a wind turbine under flow conditions typically observed at the wind farm scale, in complex terrain. A scale model wind turbine was placed in a fully developed turbulent boundary layer flow obtained in the SAFL Wind Tunnel. Experiments focused on the performance of a turbine model, under the effects induced by a second upwind turbine or a by three-dimensional, sinusoidal hill, peaking at the turbine hub height. High frequency measurements of fluctuating streamwise and wall normal velocities were obtained with a X-wire anemometer simultaneously with the rotor angular velocity and the turbine(s) voltage output. Velocity measurements in the wake of the first turbine and of the hill were used to determine the inflow conditions for the downwind test turbine. Turbine performance was inferred by the mean and fluctuating voltage statistics. Specific experiments were devoted to relate the mean voltage to the mean hub velocity, and the fluctuating voltage to the unsteadiness in the rotor kinematics induced by the perturbed (hill or turbine) or unperturbed (boundary layer) large scales of the incoming turbulent flow. Results show that the voltage signal can be used to assess turbine performance in complex flows. [Preview Abstract] |
Tuesday, November 20, 2012 8:39AM - 8:52AM |
M31.00004: PIV and Acoustic Investigation for a 2D Wind Turbine Airfoil Guannan Wang, Mark Glauser This study investigated the aerodynamic characteristics of a 2D airfoil designed for wind turbine applications using PIV and surface pressure measurements. The experiments were carried out in a low speed wind tunnel with/without large scale unsteadiness in the flow and with/without active closed loop blowing control on the suction surface of the airfoil. This study also measured the acoustic signal emitted from the same type of airfoil with six far field microphones in an anechoic chamber and the results indicated that the unsteadiness in the freestream affected the noise characteristics of the airfoil significantly. [Preview Abstract] |
Tuesday, November 20, 2012 8:52AM - 9:05AM |
M31.00005: Efficiency and flow structure of vertical-axis turbines with an upstream deflecting plate Daegyoum Kim, Morteza Gharib The power generation and flow structure of straight-bladed vertical-axis turbines with an upstream deflector are investigated experimentally in tunnel facilities. When an upstream deflecting plate is normal to flow direction, a region of low velocity is formed in its near-wake. However, the flow speed outside the near-wake region becomes higher than the free-stream speed. Since blades outside the wake encounter higher flow velocity, they can rotate with higher torque and rotating speed compared to the case without an upstream deflector, which results in power output increase. Here, we study the effect of deflector position and width on the efficiency of vertical turbines. We also discuss the flow structure generated by the deflector system. [Preview Abstract] |
Tuesday, November 20, 2012 9:05AM - 9:18AM |
M31.00006: Start-up dynamics of vertical axis turbines Katherine Taylor, John Dabiri We present an experimental study of the self-starting behavior of vertical axis turbines, in order to guide the design of systems that operate in unsteady flows. The torque, angular velocity, and power generation of a scale model turbine were measured in a free surface water tunnel for different starting angles of the rotor blades and for different flow speeds. The starting behavior of the turbine was found to be sensitively dependent on the initial angle of the rotor at low flow speeds. A conceptual model was developed in order to explain the observed behavior in terms of the instantaneous lift and drag on the rotor blades. [Preview Abstract] |
Tuesday, November 20, 2012 9:18AM - 9:31AM |
M31.00007: The Influence of Rotor Configurations on the Energy Production in an Array of Vertical-Axis Wind Turbines Matthias Kinzel, Daniel Araya, John Dabiri We analyze the flow field within an array of 18 vertical-axis wind turbines (VAWTs) at full-scale and under natural wind conditions. The emphasis is on the energy flux into the turbine array and the energy extraction by the turbines. The wind velocities throughout the turbine array are measured using a portable meteorological tower with seven, vertically-staggered, three-component ultrasonic anemometers. These measurements yield a detailed insight into the turbine wakes and the recovery of the flow. A high planform kinetic energy flux is detected, which enables the flow velocities to return to 95{\%} of the upwind value within six rotor diameters downwind from a turbine row. This is significantly faster than the recovery behind a typical horizontal-axis wind turbine (HAWT). The Presentation will compare the results for different rotor configurations. Conclusions will be drawn about the influence of these configurations on the power production of the individual turbines as well as the turbine array as a whole. [Preview Abstract] |
Tuesday, November 20, 2012 9:31AM - 9:44AM |
M31.00008: Effect of turbulence intensity on power generation in a 4x3 wind turbine array Murat Tutkun, Elizabeth Camp, Raul Bayoan Cal Turbulence intensity is highly variable in the atmospheric boundary layer. This is the typical environment where wind farms are placed and operate. The characteristics of the turbulence have the ability to impact the power production of wind turbines. Here, a wind tunnel study on a 4x3 wind turbine array is performed in which the turbulence intensity is varied independently. These experiments are carried out in a wind tunnel setting and the power is measured using torque and angular frequency sensing devices. The levels of turbulence are varied via a dynamic grid. Three cases are obtained one passive and two active (with two distinct ranges). Power production along the centerline of the array was measured for each of the cases using model turbines outfitted with torque sensors. [Preview Abstract] |
Tuesday, November 20, 2012 9:44AM - 9:57AM |
M31.00009: Direct power measurements on wind turbine array configurations Dominic DeLucia, Raul Bayoan Cal The reliability on the power extraction through wind turbines is an area of need given the increasing size of the arrays and energy demand. The turbulence effects generated by wind turbines on the subsequent rows downstream are assessed. Mechanical torque on the hubs of the model wind turbine is recorded and the power is calculated, where the measurements are performed in the Portland State University wind tunnel. Simultaneous torque and angular frequency of the rotors is record at three locations in a 3 by 4 wind turbine array. In this study, the effects due to in-line and staggered configurations are investigated. The base case configuration is a 3 by 4 array with a 6D downstream spacing and a 3D transverse spacing. The results are compared to wind turbine arrays of different spacing configurations. The trends in the data suggest the power is significantly increased when the downstream position are offset by 1.5D in the transverse direction not only for subsequent turbines but also when the turbines are staggered. [Preview Abstract] |
Tuesday, November 20, 2012 9:57AM - 10:10AM |
M31.00010: On the characteristic features of wind-turbine tip vortices: A wind tunnel experiment David Green, Leonardo Chamorro, Roger Arndt, Fotis Sotiropoulos, Jian Sheng Understanding the complex interaction between the vortical flow structures shed by Horizontal Axis Wind Turbines (HAWT) and the turbulent flow is crucial to optimize blade design and momentum recovery in the turbine wake, which defines the wind farm layout. Tip vortices shed by the blades play a key role in shaping up the wake behind a HAWT. Phase-locked Particle Image Velocimetry (PIV) is employed to measure mean wake, flow fluctuations, and subsequently identify large-scale coherent flow structures. Twelve consecutive downstream locations up to twelve rotor diameters and three upstream locations up to three rotor diameters are measured. Experiments are conducted at Reynolds numbers of Re=3x10$^{5}$, 4x10$^{5}$ and 12x10$^{5}$ based on the rotor diameter. To achieve sufficient spatial resolution, two fields are taken at each streamwise location to cover the upper and lower half of the model turbine. It is found that tip vortices above the turbine hub have clear structural identity as they are advected downstream. Instead of following the expanding trend of mean wake, they converge. In the lower region, the identities of tip vortices remain only one rotor diameter downstream and merge into the mean near wake. Robust statistical analysis on velocity fluctuations, Reynolds stresses, and TKE budget will be discussed. [Preview Abstract] |
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