Development of a Wind Plant Large-Eddy Simulation with Measurement-Driven Atmospheric Inflow: Preprint PDF Download
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Languages : en
Pages : 0
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This paper details the development of an aeroelastic wind plant model with large-eddy simulation (LES). The chosen LES solver is the Simulator for Wind Farm Applications (SOWFA) based on the OpenFOAM framework, coupled to NREL's comprehensive aeroelastic analysis tool, FAST. An atmospheric boundary layer (ABL) precursor simulation was constructed based on assessments of meteorological tower, lidar, and radar data over a 3-hour window. This precursor was tuned to the specific atmospheric conditions that occurred both prior to and during the measurement campaign, enabling capture of a night-to-day transition in the turbulent ABL. In the absence of height-varying temperature measurements, spatially averaged radar data were sufficient to characterize the atmospheric stability of the wind plant in terms of the shear profile, and near-ground temperature sensors provided a reasonable estimate of the ground heating rate describing the morning transition. A full aeroelastic simulation was then performed for a subset of turbines within the wind plant, driven by the precursor. Analysis of two turbines within the array, one directly waked by the other, demonstrated good agreement with measured time-averaged loads.
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Languages : en
Pages : 0
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Book Description
This paper details the development of an aeroelastic wind plant model with large-eddy simulation (LES). The chosen LES solver is the Simulator for Wind Farm Applications (SOWFA) based on the OpenFOAM framework, coupled to NREL's comprehensive aeroelastic analysis tool, FAST. An atmospheric boundary layer (ABL) precursor simulation was constructed based on assessments of meteorological tower, lidar, and radar data over a 3-hour window. This precursor was tuned to the specific atmospheric conditions that occurred both prior to and during the measurement campaign, enabling capture of a night-to-day transition in the turbulent ABL. In the absence of height-varying temperature measurements, spatially averaged radar data were sufficient to characterize the atmospheric stability of the wind plant in terms of the shear profile, and near-ground temperature sensors provided a reasonable estimate of the ground heating rate describing the morning transition. A full aeroelastic simulation was then performed for a subset of turbines within the wind plant, driven by the precursor. Analysis of two turbines within the array, one directly waked by the other, demonstrated good agreement with measured time-averaged loads.
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Category : Aerodynamics
Languages : en
Pages : 19
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Languages : en
Pages : 21
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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.
Author: Nikola Marjanovic
Publisher:
ISBN:
Category :
Languages : en
Pages : 124
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Energy production from wind is an increasingly important component of overall global power generation, and will likely continue to gain an even greater share of electricity production as world governments attempt to mitigate climate change and wind energy production costs decrease. Wind energy generation depends on wind speed, which is greatly influenced by local and synoptic environmental forcings. Synoptic forcing, such as a cold frontal passage, exists on a large spatial scale while local forcing manifests itself on a much smaller scale and could result from topographic effects or land-surface heat fluxes. Synoptic forcing, if strong enough, may suppress the effects of generally weaker local forcing. At the even smaller scale of a wind farm, upstream turbines generate wakes that decrease the wind speed and increase the atmospheric turbulence at the downwind turbines, thereby reducing power production and increasing fatigue loading that may damage turbine components, respectively. Simulation of atmospheric processes that span a considerable range of spatial and temporal scales is essential to improve wind energy forecasting, wind turbine siting, turbine maintenance scheduling, and wind turbine design. Mesoscale atmospheric models predict atmospheric conditions using observed data, for a wide range of meteorological applications across scales from thousands of kilometers to hundreds of meters. Mesoscale models include parameterizations for the major atmospheric physical processes that modulate wind speed and turbulence dynamics, such as cloud evolution and surface-atmosphere interactions. The Weather Research and Forecasting (WRF) model is used in this dissertation to investigate the effects of model parameters on wind energy forecasting. WRF is used for case study simulations at two West Coast North American wind farms, one with simple and one with complex terrain, during both synoptically and locally-driven weather events. The model's performance with different grid nesting configurations, turbulence closures, and grid resolutions is evaluated by comparison to observation data. Improvement to simulation results from the use of more computationally expensive high resolution simulations is only found for the complex terrain simulation during the locally-driven event. Physical parameters, such as soil moisture, have a large effect on locally-forced events, and prognostic turbulence kinetic energy (TKE) schemes are found to perform better than non-local eddy viscosity turbulence closure schemes. Mesoscale models, however, do not resolve turbulence directly, which is important at finer grid resolutions capable of resolving wind turbine components and their interactions with atmospheric turbulence. Large-eddy simulation (LES) is a numerical approach that resolves the largest scales of turbulence directly by separating large-scale, energetically important eddies from smaller scales with the application of a spatial filter. LES allows higher fidelity representation of the wind speed and turbulence intensity at the scale of a wind turbine which parameterizations have difficulty representing. Use of high-resolution LES enables the implementation of more sophisticated wind turbine parameterizations to create a robust model for wind energy applications using grid spacing small enough to resolve individual elements of a turbine such as its rotor blades or rotation area. Generalized actuator disk (GAD) and line (GAL) parameterizations are integrated into WRF to complement its real-world weather modeling capabilities and better represent wind turbine airflow interactions, including wake effects. The GAD parameterization represents the wind turbine as a two-dimensional disk resulting from the rotation of the turbine blades. Forces on the atmosphere are computed along each blade and distributed over rotating, annular rings intersecting the disk. While typical LES resolution (10-20 m) is normally sufficient to resolve the GAD, the GAL parameterization requires significantly higher resolution (1-3 m) as it does not distribute the forces from the blades over annular elements, but applies them along lines representing individual blades. In this dissertation, the GAL is implemented into WRF and evaluated against the GAD parameterization from two field campaigns that measured the inflow and near-wake regions of a single turbine. The data-sets are chosen to allow validation under the weakly convective and weakly stable conditions characterizing most turbine operations. The parameterizations are evaluated with respect to their ability to represent wake wind speed, variance, and vorticity by comparing fine-resolution GAD and GAL simulations along with coarse-resolution GAD simulations. Coarse-resolution GAD simulations produce aggregated wake characteristics similar to both GAD and GAL simulations (saving on computational cost), while the GAL parameterization enables resolution of near wake physics (such as vorticity shedding and wake expansion) for high fidelity applications. For the first time, to our knowledge, this dissertation combines the capabilities of a mesoscale weather prediction model, LES, and high-resolution wind turbine parameterizations into one model capable of simulating a real array of wind turbines at a wind farm. WRF is used due to its sophisticated environmental physics models, frequent use in the atmospheric modeling community, and grid nesting with LES capabilities. Grid nesting is feeding lateral boundary condition data from a coarse resolution simulation to a finer resolution simulation contained within the coarse resolution simulation's domain. WRF allows the development of a grid nesting strategy from synoptic-scale to microscale LES relevant for wind farm simulations; this is done by building on the results from the investigation of model parameters for wind energy forecasting and the implementation of the GAD and GAL wind turbine parameterizations. The nesting strategy is coupled with a GAD parameterization to model the effects of wind turbine wakes on downstream turbines at a utility-scale Oklahoma wind farm. Simulation results are compared to dual-Doppler measurements that provide three-dimensional fields of horizontal wind speed and direction. The nesting strategy is able to produce realistic turbine wake effects, while differences with the measurements can mostly be attributed to the quality of the available weather input data.
Author: John C. Wyngaard
Publisher: Cambridge University Press
ISBN: 1139485520
Category : Science
Languages : en
Pages : 407
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Based on his over forty years of research and teaching, John C. Wyngaard's textbook is an excellent up-to-date introduction to turbulence in the atmosphere and in engineering flows for advanced students, and a reference work for researchers in the atmospheric sciences. Part I introduces the concepts and equations of turbulence. It includes a rigorous introduction to the principal types of numerical modeling of turbulent flows. Part II describes turbulence in the atmospheric boundary layer. Part III covers the foundations of the statistical representation of turbulence and includes illustrative examples of stochastic problems that can be solved analytically. The book treats atmospheric and engineering turbulence in a unified way, gives clear explanation of the fundamental concepts of modeling turbulence, and has an up-to-date treatment of turbulence in the atmospheric boundary layer. Student exercises are included at the ends of chapters, and worked solutions are available online for use by course instructors.
Author: Wolfgang Rodi
Publisher: CRC Press
ISBN: 0203797574
Category : Technology & Engineering
Languages : en
Pages : 266
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Book Description
An introduction to the Large-Eddy-Simulation (LES) method, geared primarily toward hydraulic and environmental engineers, the book covers special features of flows in water bodies and summarizes the experience gained with LES for calculating such flows. It can also be a valuable entry to the subject of LES for researchers and students in all fields of fluids engineering, and the applications part will be useful to researchers interested in the physics of flows governed by the dynamics of coherent structures.
Author: Adam Lavely
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Modern utility-scale wind turbines operate in the the lower atmospheric boundary layer (ABL), which is characterized by large gradients in mean velocity and temperature and the existence of strong coherent turbulence eddies that reflect the interaction between strong mean shear and vertical buoyancy driven by solar heating. The spatio-temporal velocity variations drive nonsteady loadings on wind turbines that contribute to premature wind turbine component fatigue failure, decreasing the levelized cost of (wind) energy (LCOE). The aims of the current comprehensive research program center on the quantification of the characteristics of the nonsteady loads resulting from the interactions between the coherent energy contain gin atmospheric turbulence eddies within the lower ABL as the eddies advect through the rotor plane and the rotating wind turbine blade encounter the internal turbulence structure of the atmospheric eddies.We focus on the daytime atmospheric boundary layer, where buoyancy due to surface heating interacts with shear to create coherent turbulence structures. Pseudo-spectral large eddy simulation (LES) is used to generate an equilibrium atmospheric boundary layer over flat terrain with uniform surface roughness characteristic of the Midwest on a typical sunny windy afternoon when the ABL can be approximated as quasi-steady. The energy-containing eddies are found to create advective time-responses of order 30-90 seconds with lateral spatial scales of order the wind turbine rotor diameter. Different wind turbine simulation methods of a representative utility scale turbine were applied using the atmospheric turbulence as inflow.We apply three different fidelity wind turbine simulation methods to quantify the extent to which lower order models are able to accurately predict the nonsteady loading due to atmospheric turbulence eddies advecting through the rotor plane and interacting with the wind turbine. The methods vary both the coupling to the atmospheric boundary layer and the way in which the blade geometry is resolved and sectional blade forces are calculated. The highest fidelity simulation resolves the blade geometry to capture unsteady boundary layer response and separation dynamics within a simulation of the atmospheric boundary layer coupling the effect of the turbine to the atmospheric inflow. The lower order models both use empirical look-up tables to predict the time changes in blade sectional forces as a function of time changes in local velocity vector. The actuator line method (ALM) is two-way coupled and feeds these blade forces back into a simulation of the atmospheric boundary layer. The blade element momentum theory (BEMT) is one-way coupled and models the effect of the turbine on the incoming velocity field. The coupling method and method of blade resolution are both found to have an effect on the ability to accurately predict sectional blade load response to nonsteady atmospheric turbulence. The BEMT cannot accurately predict the timing of the response changes as these are modulated by the wind turbine within the ABL simulations. The lower order models have increased blade sectional load range and temporal gradients due to their inability to accurately capture the temporal response of the blade geometry to inflow changes. Taking advantage of horizontal homogeneity to collect statistics, we investigate the time period required to create well converged statistics in the equilibrium atmospheric boundary layer and find whereas the 10-minute industry standard for `averages' retains variability of order 10%, the 10-minute average is an optimal choice. We compare the industry standard 10-minute averaging period. The residual variability within the 10-minute period to the National Renewable Energy Laboratory (NREL) Gearbox Reliability Collaborative (GRC) field test database to find that whereas the 10-minute window still contains large variability, it is, in some sense, optimal because averaging times much longer would be required to significantly reduce variability. Turbulence fluctuations in streamwise velocity are found to be the primary driver of temporal variations in local angles of attack and sectional blade loads. Based on this new understanding, we develop analyses to show that whereas rotor torque and thrust correlate well with upstream horizontal velocity averaged over the rotor disk, out-of-plane bending moment magnitude correlates with the asymmetry in the horizontal fluctuating velocity over the rotor disk. Consequentially, off-design motions of the drivetrain and gearbox shown with the GRC field test data are well predicted using an asymmetry index designed to capture the response of a three-bladed turbine to asymmetry in the rotor plane. The predictors for torque, thrust and out-of-plane bending moment are shown to correlate well to upstream rotor planes indicating that they may be applied to advanced feed-forward control methods such as forward-facing LIDAR used to detect velocity changes in front of a wind turbine. This has the potential to increase wind turbine reliability by using controls to reduce potentially detrimental load responses to incoming atmospheric turbulence and decrease the LCOE.
Author: Anthony Rey DeLeon
Publisher:
ISBN: 9780355067743
Category : Turbulence
Languages : en
Pages : 464
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Book Description
As the percentage of wind energy continues to increase in the overall energy portfolio, two essential components of integrating wind energy are designing wind turbines to withstand the forces created by the wind and correctly predicting the power production from wind farms. Accurate wind modeling over complex terrain is paramount to both applications. Existing wind forecasting techniques use computational resolutions on the order of a kilometer, whether the terrain be flat or complex. In this dissertation, a computational framework that applies the large-eddy simulation (LES) technique with resolutions on the order of 10 m is developed to improve predictions of turbulent winds over complex terrain. LES is a computationally expensive technique and a distinguishing aspect of the proposed framework is that the entire simulation is developed for massive-parallelism using clusters of graphics process units (GPUs). To reduce the near-wall resolution requirements, Reynolds-averaged Navier-Stokes (RANS) is used in tandem with LES as a wall-model. The hybrid use of RANS and LES leads to modeling artifacts such as a mismatch in the theoretical logarithmic law-of-the wall. A forcing technique that splits the driving mean pressure gradient based on conservation of mass principle is proposed. The split-forcing approach was found to reduce the modeling artifacts on coarse grids. A new turbulent inflow condition based on buoyancy perturbations is proposed for both smooth-wall-engineering and complex-terrain flows. For complex terrain winds, an improved immersed-boundary method is developed based on the equilibrium assumptions in the atmospheric surface layer, along with a pre-processor to process terrain geometry. The computational framework and individual components are thoroughly tested and validated using well-known benchmark cases. Finally, the computational framework is applied to study the feasibility of dynamic line-rating concept over complex terrain. Potential avenues of further research are also recommended.
Author: Jesper Grønnegaard Pedersen
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Oumnia El Fajri
Publisher:
ISBN:
Category :
Languages : en
Pages : 90
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Atmospheric boundary layer flows around wind turbines distributed in a large wind farm can be examined by the use of large eddy simulation (LES), which is based on the assumption that large eddies in the flow are anisotropic and depend on the mean flow and the configuration geometry, while smaller eddies are isotropic and homogeneous, and can be modeled via subgrid scale models. In this thesis, a pseudo-spectral LES code with inflow conditions imposed through a precursor concurrent simulation is utilized to model the flow around a single wind turbine or a large wind farm operating in thermallystratified conditions. The effect of the wind turbines on humidity is monitored through an additional scalar convection equation. It is found that on average, the effect of an individual wind turbine on the humidity is less than 1%, while the effect of the wind farm on humidity can reach 1-2% in the cumulative wakes.
