Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session Q03: Energy Harvesting and Power Generation III |
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Chair: Richard Stevens, University of Twente Room: Georgia World Congress Center B204 |
Tuesday, November 20, 2018 12:50PM - 1:03PM |
Q03.00001: The effects of freestream turbulence and shear flows on the near-field wake of a lab-scale wind turbine Leon Li, R. Jason Hearst, Bharathram Ganapathisubramani Wind turbines experience a wide range of turbulent shear flows within the atmospheric boundary layer, which is challenging to replicate in a wind tunnel setting. The classical methods of using passive flow conditioning devices to modify wind tunnel boundary layers has had limited success due to their inherent inability to separate shear from turbulence intensity. The present study uses an active grid to decouple shear and turbulence intensity in order to investigate their separate effects on the near field wake of a wind turbine model. A total of 7 flow profiles were created that covered a wide range of turbulence intensities and shear profiles. PIV results show that incoming flow conditions do not have a major influence on wake geometry compared to the incoming flow. Turbulence production in the wake under shear conditions skews toward the high velocity side. This in turn leads to higher variance in the local wake boundary. The behaviour of the hub velocity contour line before and after the blades are affected by shear only. Overall the macroscopic properties of the wake are not affected by incoming flow conditions, however shear has greater impact on velocity profile and turbulence production within the wake than turbulence intensity. |
Tuesday, November 20, 2018 1:03PM - 1:16PM |
Q03.00002: Acoustic tomography of turbulent flows near wind turbines Nicholas Hamilton, James Hansen, Julie Lundquist, Patrick Moriarty, Vladimir Ostashev Acoustic tomography of the atmosphere is a relatively unexplored remote sensing technology with the potential to improve fundamental scientific knowledge of atmospheric turbulence and acoustic wave propagation in the atmosphere and potential to expand our capabilities in terms of wind turbine wake observations. Existing remote sensing technologies rely on wave backscatter off of airborne particulate matter, which limits spatial and temporal resolution and cannot produce reliable flow estimates near solid bodies. In contrast, acoustic tomography relies on the direct travel of signals between transducers in a network and can achieve much higher resolutions in space and time. Signal travel times are combined using a stochastic inversion technique to reconstruct both the velocity and temperature fields within the transducer network. An acoustic tomography array at the National Wind Technology Center has been developed to investigate atmospheric flows from which energy is extracted by utility scale wind turbines and to make observations around wind turbines to illuminate wake physics and provide highly resolved observations necessary for high-fidelity model validation efforts. |
Tuesday, November 20, 2018 1:16PM - 1:29PM |
Q03.00003: A laboratory study on the effect of incoming turbulence on the performance of wind turbines Stefano Gambuzza, Bharathram Ganapathisubramani Performance of wind turbines varies significantly with the nature of the incoming flow, especially when under free stream turbulence. Given the complexity of an analytical approach, experimental and computational studies have been undertaken to quantify performance changes. Simplified actuator disk simulations cannot obtain performance figures, and more complicated models are computationally expensive. Experimental studies can measure performance indices, but it is hard to generate consistent free stream turbulence. This study aims to address these problems by experimentally measuring the power and thrust values of a model wind turbine (with a rotor diameter of 180 mm). In order to obtain consistent values of free stream turbulence, an active grid is used to vary the turbulence index from 0 to 10%, with an integral length scale comparable to the rotor diameter. Measurements of generated power are obtained by means of a brushed DC motor, whose angular velocity was varied by changing the electrical load on the poles. Angular velocity, power and their fluctuations have been measured. The turbine was operated in different yawed configurations to examine the effect of wind direction. Hot-wire measurements are also obtained in the wake and the final talk will present results. |
Tuesday, November 20, 2018 1:29PM - 1:42PM |
Q03.00004: Wind turbines fitted with hydrostatic transmission: performance and turbulence effects Helber Antonio Esquivel, Michael Roggenburg, Eduardo Fenollal, David Warsinger, Jose Garcia, Monika Ivantysynova, Andrea Vacca, Leonardo P Chamorro, Humberto Bocanegra-Evans, Luciano Castillo In this work, we examine the potential advantages of using hydrostatic transmission over the traditional gearbox systems on horizontal-axis wind turbines. For this purpose, a series of controlled input experiments were performed at various inflow conditions. The power curve of the wind turbine as function of the tip-speed ratio shows an increase in the hydrostatic transmission and the operational cut-in speed. Significant benefits of the hydraulic wind turbine include the reduced weight and the placement of key components at ground level, which leads to greater floating stability over the traditional drive train in the hub. This is particularly useful for offshore applications, where substantial reduction of the cost of energy cost production is clearly possible; on the order of 20%. Furthermore, the displacement of the center of gravity near to the base of the turbine allows for greater stability in floating platforms. Based on the power spectrum model of Tobin et al (2015), we explore the power spectral response of the hydraulic wind turbine and assess the impact of turbulence on the power production with HST and regular drivetrain. |
Tuesday, November 20, 2018 1:42PM - 1:55PM |
Q03.00005: Abstract Withdrawn
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Tuesday, November 20, 2018 1:55PM - 2:08PM |
Q03.00006: Boundary-layer evolution over wind farms Antonio Segalini The recent growth of wind energy has boosted the development of many large wind farms where the clustering of the turbines helps reducing installation costs. However, the ambient turbulence is expected to grow substantially due to the turbines presence, and the turbines cannot be considered as individuals but have a global effect as a whole. Kinetic energy transfer from the region above the turbines is expected indeed to play a key role to replenish the energy content of the flow passing the turbines rotor. In the present work, the flow over a large wind farm (composed by several freely-rotating wind-turbine models) is studied through a wind-tunnel campaign with hot-wire anemometry. 152 turbines were mounted with 19 subsequent rows, allowing to go beyond the adjustment region of the internal boundary layer located in the first rows. All the three velocity components were measured, providing a good characterisation of the Reynolds-stress tensor. The balance of advection, turbine thrust force and turbulence rules such a growth according to an integrated form of the Navier-Stokes equations. The possibility of a self-similar evolution of the velocity profile and of the Reynolds stresses will be further investigated. |
Tuesday, November 20, 2018 2:08PM - 2:21PM |
Q03.00007: Data-driven yaw optimization of a full-scale 60 MW wind farm Michael F. Howland, Sanjiva K Lele, John O. Dabiri Due to the prevalence of wake interactions in large, utility-scale horizontal axis wind farms, wake steering based power optimization has received significant recent attention. Upstream wind turbines may intentionally misalign the axis of rotation with respect to the incoming wind to create a yaw angle. The misalignment of thrust force and wind velocity vectors results in a lateral deflection of the momentum deficit region behind the yawed wind turbine. While the yawing of a turbine decreases its power production, it enhances the performance of the downstream turbine due to the deflection of the wake. Recent literature has proposed a supplement to wake models which accounts for the wake deflection in yawed conditions. Model parameters for low-order wake models are calibrated using five years of operational power SCADA data from a 60 MW wind farm. The low-order wake models are used to improve the power production of the operational wind farm through the use of a novel optimization technique. Various optimization algorithms and wake models are also compared to study sensitivity and robustness. |
Tuesday, November 20, 2018 2:21PM - 2:34PM |
Q03.00008: Wind Turbine Performance in Very Large Wind Farms: Energy and Momentum Budgets for a Streamtube Jacob R West, Sanjiva K Lele In this study, we analyze a wind turbine in a large wind farm with the same streamtube approach used to derive the Betz limit. Using large eddy simulations (LES) of a periodic array of actuator disks in a channel flow, we present mean momentum and mean kinetic energy budgets for a range of thrust coefficients. Our results compare favorably with the theory of Nishino (TORQUE, 2016) for predicting wind turbine power coefficient from only the wind farm layout, local thrust coefficient, and ground roughness height. The maximum power coefficient found is smaller than the Betz limit for an isolated turbine, and is maximized by a smaller value of the thrust coefficient as well. The optimal thrust coefficient is found to be the one which maximizes the work done by Reynolds stresses on the surface of the streamtube. Increasing the thrust coefficient promotes turbulent mixing and faster wake recovery, but also slows the mean flow, resulting in the observed tradeoff. We compare with LES of an isolated actuator disk interacting with homogeneous turbulent inflow, and find that turbulence and the presence of other turbines both contribute to deviations from the idealized Betz picture. |
Tuesday, November 20, 2018 2:34PM - 2:47PM |
Q03.00009: Large-eddy simulation of a utility-scale wind farm in complex terrain Xiaolei Yang, Maggie Pakula, Fotis Sotiropoulos Site-specific wind farm design must take into account the effects of site-specific terrain topography. Large-eddy simulation (LES) is a promising approach for simulating the site-specific characteristics of the wind fields and turbine wakes in complex terrain. In this work, we apply the state-of-art LES code Virtual Flow Simulator (VFS-Wind) to simulate the Invenergy Vantage wind farm in complex terrain. The computed power outputs are compared with field measurements and good agreement with the measured data is obtained. A simple analytical wind farm model without considering the complex terrain effects is also applied to predict the performance of the Vantage wind farm layout. The results show that such a model overestimates the performance of the actual Vantage wind farm and underscore the need for developing analytical models that account for terrain effects to enable wind farm design and optimization in complex terrain. |
Tuesday, November 20, 2018 2:47PM - 3:00PM |
Q03.00010: The performance of ocean current turbine arrays operating in a shear flow Peyman Razi, Praveen Ramaprabhu, Christopher Vermillion We use numerical simulations and reduced order wake interaction models to describe the performance of an array of ocean current turbines (OCTs) operating in a spatially nonuniform inlet flow field. In particular, we are interested in linear shear profiles of varying strengths and reminiscent of conditions found in the Gulf Stream. An analytical model proposed by [1] for turbines operating in arbitrary velocity profiles is extended here to the case of multiple devices, accounting properly for the wake interaction effects. The predictions from the resulting model are compared with RANS numerical simulations performed using the STAR-CCM software. In the simulations, the turbines are represented as porous disks through an Actuator Disk model (ADM), while the turbulence is modeled using the k-omega turbulence closure. A parametric variation across different non-dimensional shear rates and turbine induction factors was also carried out. The results from this study can be generalized to wind turbine farms and airborne, tethered wind energy systems. 1 L.P. Chamorro, and R.E.A. Arndt, Wind Energy, 16, 279-282 (2013) |
Tuesday, November 20, 2018 3:00PM - 3:13PM |
Q03.00011: Finding the optimal soft material for the blades to improve wind turbine versatility. Vincent Cognet, Sylvain Courrech du Pont, Benjamin Thiria Although pitch angle control enlarges the working range of Horizontal Axis Wind Turbine (HAWT), this active method is expensive, energy consuming and requires maintenance. Passive pitch control, using soft materials for the blades, proposes an interesting alternative. It has been shown that reconfiguration of flexible blades with respect to tip speed ratio λ is governed by three dimensionless numbers: the initial pitch angle θ0, the Cauchy number CY (ratio between aerodynamic forces on the blade and elastic returning force), and the centrifugal number CC (ratio between centrifugal force and elastic returning force) [1]. In this presentation, we introduce a new procedure which finds the optimal set (θ0, CY, CC)opt corresponding to the soft materials able to passively reproduce the optimal deformation of the blade (ie the optimal variation of pitch angle θ with respect to λ) [2]. The procedure integrates BEM theory and works for constant wind velocity U, for constant angular velocity Ω, for constant resistive torque C, and for a torque proportional to angular velocity. [1] V. Cognet et al. 2017. Bioinspired turbine blades offer new perspective for wind energy [2] V. Cognet et al. 2017. Deformable blades to optimize rotors efficiency (Patent)
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Tuesday, November 20, 2018 3:13PM - 3:26PM |
Q03.00012: Investigating the benefits of vertical staggering and optimizing turbine layout Jessica Strickland, Richard Stevens The growing population is placing increased stress on both energy and land resources making strategic wind farm development a necessity. Power output optimization requires understanding wake effects caused by preceding turbines within a wind farm. Alternating large and small turbines could be advantageous by mitigating wake effects and by potentially increasing the turbulent vertical kinetic energy flux, which would facilitate wake recovery. However, the use of vertical staggering is still relatively unexplored. We have improved upon a ‘top-down’ analytical model (Xie et al. Wind Energy 20, 45–62 (2017)) which is applied to periodic, vertically staggered wind farms. The model predictions are compared to large eddy simulations results. The analytical model is used to investigate the optimal spacing and profitability of vertically staggered wind farms to determine in which cases such a layout is beneficial. This work is applicable to retro-fitting present wind farms as available land area becomes increasingly limited. We discuss the effect of the main wind farm design parameters such as the turbine diameter, height, and spacing on the potential effectiveness of using vertical staggering with large and small turbines. |
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