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Large-Eddy Simulation Study of Wake Propagation and Power Production in an Array of Tidal-Current Turbines: Preprint

Description: This paper presents our initial work in performing large-eddy simulations of tidal turbine array flows. First, a horizontally-periodic precursor simulation is performed to create turbulent flow data. Then that data is used as inflow into a tidal turbine array two rows deep and infinitely wide. The turbines are modeled using rotating actuator lines, and the finite-volume method is used to solve the governing equations. In studying the wakes created by the turbines, we observed that the vertical shear of the inflow combined with wake rotation causes lateral wake asymmetry. Also, various turbine configurations are simulated, and the total power production relative to isolated turbines is examined. Staggering consecutive rows of turbines in the simulated configurations allows the greatest efficiency using the least downstream row spacing. Counter-rotating consecutive downstream turbines in a non-staggered array shows a small benefit. This work has identified areas for improvement, such as the use of a larger precursor domain to better capture elongated turbulent structures, the inclusion of salinity and temperature equations to account for density stratification and its effect on turbulence, improved wall shear stress modelling, and the examination of more array configurations.
Date: July 1, 2012
Creator: Churchfield, M. J.; Li, Y. & Moriarty, P. J.
Partner: UNT Libraries Government Documents Department

Atmospheric and Wake Turbulence Impacts on Wind Turbine Fatigue Loading: Preprint

Description: Large-eddy simulations of atmospheric boundary layers under various stability and surface roughness conditions are performed to investigate the turbulence impact on wind turbines. In particular, the aeroelastic responses of the turbines are studied to characterize the fatigue loading of the turbulence present in the boundary layer and in the wake of the turbines. Two utility-scale 5 MW turbines that are separated by seven rotor diameters are placed in a 3 km by 3 km by 1 km domain. They are subjected to atmospheric turbulent boundary layer flow and data is collected on the structural response of the turbine components. The surface roughness was found to increase the fatigue loads while the atmospheric instability had a small influence. Furthermore, the downstream turbines yielded higher fatigue loads indicating that the turbulent wakes generated from the upstream turbines have significant impact.
Date: December 1, 2011
Creator: Lee, S.; Churchfield, M.; Moriarty, P.; Jonkman, J. & Michalakes, J.
Partner: UNT Libraries Government Documents Department

Acoustic Array Development for Wind Turbine Noise Characterization

Description: This report discusses the design and use of a multi-arm, logarithmic spiral acoustic array by the National Renewable Energy Laboratory (NREL) for measurement and characterization of wind turbine-generated noise. The array was developed in collaboration with a team from the University of Colorado Boulder. This design process is a continuation of the elliptical array design work done by Simley. A description of the array system design process is presented, including array shape design, mechanical design, design of electronics and the data acquisition system, and development of post-processing software. System testing and calibration methods are detailed. Results from the initial data acquisition campaign are offered and discussed. Issues faced during this initial deployment of the array are presented and potential remedies discussed.
Date: November 1, 2013
Creator: Buck, S.; Roadman, J.; Moriarty, P. & Palo, S.
Partner: UNT Libraries Government Documents Department

Sensitivity Analysis of Offshore Wind Cost of Energy (Poster)

Description: No matter the source, offshore wind energy plant cost estimates are significantly higher than for land-based projects. For instance, a National Renewable Energy Laboratory (NREL) review on the 2010 cost of wind energy found baseline cost estimates for onshore wind energy systems to be 71 dollars per megawatt-hour ($/MWh), versus 225 $/MWh for offshore systems. There are many ways that innovation can be used to reduce the high costs of offshore wind energy. However, the use of such innovation impacts the cost of energy because of the highly coupled nature of the system. For example, the deployment of multimegawatt turbines can reduce the number of turbines, thereby reducing the operation and maintenance (O&M) costs associated with vessel acquisition and use. On the other hand, larger turbines may require more specialized vessels and infrastructure to perform the same operations, which could result in higher costs. To better understand the full impact of a design decision on offshore wind energy system performance and cost, a system analysis approach is needed. In 2011-2012, NREL began development of a wind energy systems engineering software tool to support offshore wind energy system analysis. The tool combines engineering and cost models to represent an entire offshore wind energy plant and to perform system cost sensitivity analysis and optimization. Initial results were collected by applying the tool to conduct a sensitivity analysis on a baseline offshore wind energy system using 5-MW and 6-MW NREL reference turbines. Results included information on rotor diameter, hub height, power rating, and maximum allowable tip speeds.
Date: October 1, 2012
Creator: Dykes, K.; Ning, A.; Graf, P.; Scott, G.; Damiami, R.; Hand, M. et al.
Partner: UNT Libraries Government Documents Department

Applications of Systems Engineering to the Research, Design, and Development of Wind Energy Systems

Description: This paper surveys the landscape of systems engineering methods and current wind modeling capabilities to assess the potential for development of a systems engineering to wind energy research, design, and development. Wind energy has evolved from a small industry in a few countries to a large international industry involving major organizations in the manufacturing, development, and utility sectors. Along with this growth, significant technology innovation has led to larger turbines with lower associated costs of energy and ever more complex designs for all major subsystems - from the rotor, hub, and tower to the drivetrain, electronics, and controls. However, as large-scale deployment of the technology continues and its contribution to electricity generation becomes more prominent, so have the expectations of the technology in terms of performance and cost. For the industry to become a sustainable source of electricity, innovation in wind energy technology must continue to improve performance and lower the cost of energy while supporting seamless integration of wind generation into the electric grid without significant negative impacts on local communities and environments. At the same time, issues associated with wind energy research, design, and development are noticeably increasing in complexity. The industry would benefit from an integrated approach that simultaneously addresses turbine design, plant design and development, grid interaction and operation, and mitigation of adverse community and environmental impacts. These activities must be integrated in order to meet this diverse set of goals while recognizing trade-offs that exist between them. While potential exists today to integrate across different domains within the wind energy system design process, organizational barriers such as different institutional objectives and the importance of proprietary information have previously limited a system level approach to wind energy research, design, and development. To address these challenges, NREL has embarked on an initiative to evaluate how methods of ...
Date: December 1, 2011
Creator: Dykes, K.; Meadows, R.; Felker, F.; Graf, P.; Hand, M.; Lunacek, M. et al.
Partner: UNT Libraries Government Documents Department

SOWFA Super-Controller: A High-Fidelity Tool for Evaluating Wind Plant Control Approaches

Description: This paper presents a new tool for testing wind plant controllers in the Simulator for Offshore Wind Farm Applications (SOWFA). SOWFA is a high-fidelity simulator for the interaction between wind turbine dynamics and the fluid flow in a wind plant. The new super-controller testing environment in SOWFA allows for the implementation of the majority of the wind plant control strategies proposed in the literature.
Date: January 1, 2013
Creator: Fleming, P.; Gebraad, P.; van Wingerden, J. W.; Lee, S.; Churchfield, M.; Scholbrock, A. et al.
Partner: UNT Libraries Government Documents Department

SOWFA + Super Controller User's Manual

Description: SOWFA + Super Controller is a modification of the NREL's SOWFA tool which allows for a user to apply multiturbine or centralized wind plant control algorithms within the high-fidelity SOWFA simulation environment. The tool is currently a branch of the main SOWFA program, but will one day will be merged into a single version. This manual introduces the tool and provides examples such that a user can implement their own super controller and set up and run simulations. The manual only discusses enough about SOWFA itself to allow for the customization of controllers and running of simulations, and details of SOWFA itself are reported elsewhere Churchfield and Lee (2013); Churchfield et al. (2012). SOWFA + Super Controller, and this manual, are in alpha mode.
Date: August 1, 2013
Creator: Fleming, P.; Gebraad, P.; Churchfield, M.; Lee, S.; Johnson, K.; Michalakes, J. et al.
Partner: UNT Libraries Government Documents Department

Large-Eddy Simulation of Wind-Plant Aerodynamics: Preprint

Description: In this work, we present results of a large-eddy simulation of the 48 multi-megawatt turbines composing the Lillgrund wind plant. Turbulent inflow wind is created by performing an atmospheric boundary layer precursor simulation and turbines are modeled using a rotating, variable-speed actuator line representation. The motivation for this work is that few others have done wind plant large-eddy simulations with a substantial number of turbines, and the methods for carrying out the simulations are varied. We wish to draw upon the strengths of the existing simulations and our growing atmospheric large-eddy simulation capability to create a sound methodology for performing this type of simulation. We have used the OpenFOAM CFD toolbox to create our solver.
Date: January 1, 2012
Creator: Churchfield, M. J.; Lee, S.; Moriarty, P. J.; Martinez, L. A.; Leonardi, S.; Vijayakumar, G. et al.
Partner: UNT Libraries Government Documents Department

Systems Engineering Applications to Wind Energy Research, Design, and Development (Poster)

Description: Over the last few decades, wind energy has evolved into a large international industry involving major players in the manufacturing, construction, and utility sectors. Coinciding with the industry's growth, significant innovation in the technology has resulted in larger turbines with lower associated costs of energy and more complex designs in all subsystems. However, as the deployment of the technology grows, and its role within the electricity sector becomes more prominent, so has the expectations of the technology in terms of performance, reliability, and cost. The industry currently partitions its efforts into separate paths for turbine design, plant design and development, grid interaction and operation, and mitigation of adverse community and environmental impacts. These activities must be integrated to meet a diverse set of goals while recognizing trade-offs between them. To address these challenges, the National Renewable Energy Laboratory (NREL) has embarked on the Wind Energy Systems Engineering (WESE) initiative to use methods of systems engineering in the research, design, and development of wind energy systems. Systems engineering is a field that has a long history of application to complex technical systems. The work completed to date represents a first step in understanding this potential. It reviews systems engineering methods as applied to related technical systems and illustrates how these methods can be combined in a WESE framework to meet the research, design, and development needs for the future of the industry.
Date: June 1, 2012
Creator: Dykes, K.; Damiani, R.; Felker, F.; Graf, P.; Hand, M.; Meadows, R. et al.
Partner: UNT Libraries Government Documents Department