The Experts below are selected from a list of 309 Experts worldwide ranked by ideXlab platform
Rebecca Jane Barthelmie - One of the best experts on this subject based on the ideXlab platform.
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CFD modelling of wind farms in Complex Terrain
2020Co-Authors: John Prospathopoulos, Daniel Cabezón Martínez, P. K. Chaviaropoulos, K. Rados, J.g. Schepers, Kurt Schaldemose Hansen, Evangelos S. Politis, Rebecca Jane BarthelmieAbstract:Modelling of entire wind farms in flat and Complex Terrain using a full 3D Navier–Stokes solver for incompressible flow is presented in this paper. Numerical integration of the governing equations is performed using an implicit pressure correction scheme, where the wind turbines (W/Ts) are modelled as momentum absorbers through their thrust coefficient. The k–ω turbulence model, suitably modified for atmospheric flows, is employed for closure. A correction is introduced to account for the underestimation of the near wake deficit, in which the turbulence time scale is bounded using a general “realizability” constraint for the fluctuating velocities. The second modelling issue that is discussed in this paper is related to the determination of the reference wind speed for the thrust calculation of the machines. Dealing with large wind farms and wind farms in Complex Terrain, determining the reference wind speed is not obvious when a W/T operates in the wake of another WT and/or in Complex Terrain. Two alternatives are compared: using the wind speed value at hub height one diameter upstream of the W/T and adopting an induction factor-based concept to overcome the utilization of a wind speed at a certain distance upwind of the rotor. Application is made in two wind farms, a five-machine one located in flat Terrain and a 43-machine one located in Complex Terrain.
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Simulation of wind farms in flat and Complex Terrain using CFD
2020Co-Authors: John Prospathopoulos, Daniel Cabezón Martínez, P. K. Chaviaropoulos, K. Rados, J.g. Schepers, Kurt Schaldemose Hansen, Evangelos S. Politis, Rebecca Jane BarthelmieAbstract:Use of computational fluid dynamic (CFD) methods to predict the power production from wind entire wind farms in flat and Complex Terrain is presented in this paper. Two full 3D Navier–Stokes solvers for incompressible flow are employed that incorporate the k–e and k–ω turbulence models respectively. The wind turbines (W/Ts) are modelled as momentum absorbers by means of their thrust coefficient using the actuator disk approach. The WT thrust is estimated using the wind speed one diameter upstream of the rotor at hub height. An alternative method that employs an induction-factor based concept is also tested. This method features the advantage of not utilizing the wind speed at a specific distance from the rotor disk, which is a doubtful approximation when a W/T is located in the wake of another and/or the Terrain is Complex. To account for the underestimation of the near wake deficit, a correction is introduced to the turbulence model. The turbulence time scale is bounded using the general “realizability” constraint for the turbulent velocities. Application is made on two wind farms, a five-machine one located in flat Terrain and another 43-machine one located in Complex Terrain. In the flat Terrain case, the combination of the induction factor method along with the turbulence correction provides satisfactory results. In the Complex Terrain case, there are some significant discrepancies with the measurements, which are discussed. In this case, the induction factor method does not provide satisfactory results.
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Simulation of Wind Farms in Flat & Complex Terrain using CFD
2020Co-Authors: John Prospathopoulos, P. K. Chaviaropoulos, K. Rados, J.g. Schepers, Daniel Cabezon, Kurt Schaldemose Hansen, Evangelos S. Politis, Rebecca Jane BarthelmieAbstract:Use of computational fluid dynamic (CFD) methods to predict the power production from wind entire wind farms in flat and Complex Terrain is presented in this paper. Two full 3D Navier–Stokes solvers for incompressible flow are employed that incorporate the k–e and k–ω turbulence models respectively. The wind turbines (W/Ts) are modelled as momentum absorbers by means of their thrust coefficient using the actuator disk approach. The WT thrust is estimated using the wind speed one diameter upstream of the rotor at hub height. An alternative method that employs an induction-factor based concept is also tested. This method features the advantage of not utilizing the wind speed at a specific distance from the rotor disk, which is a doubtful approximation when a W/T is located in the wake of another and/or the Terrain is Complex. To account for the underestimation of the near wake deficit, a correction is introduced to the turbulence model. The turbulence time scale is bounded using the general “realizability” constraint for the turbulent velocities. Application is made on two wind farms, a five-machine one located in flat Terrain and another 43-machine one located in Complex Terrain. In the flat Terrain case, the combination of the induction factor method along with the turbulence correction provides satisfactory results. In the Complex Terrain case, there are some significant discrepancies with the measurements, which are discussed. In this case, the induction factor method does not provide satisfactory results.
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Characterizing wind gusts in Complex Terrain
Atmospheric Chemistry and Physics, 2019Co-Authors: F. Letson, Rebecca Jane Barthelmie, Weifei Hu, Sara C. PryorAbstract:Abstract. Wind gusts are a key driver of aerodynamic loading, especially for tall structures such a bridges and wind turbines. However, gust characteristics in Complex Terrain are not well understood and common approximations used to describe wind gust behavior may not be appropriate at heights relevant to wind turbines and other structures. Data collected in the Perdigao experiment are analyzed herein to provide a foundation for improved wind gust characterization and process-level understanding of flow intermittency in Complex Terrain. High-resolution observations from sonic anemometers and vertically pointing Doppler lidars are used to conduct a detailed study of gust characteristics with a specific focus on the parent distributions of nine gust parameters (that describe velocity, time, and length scales), their joint distributions, height variation, and coherence in the vertical and horizontal planes. Best-fit distributional forms for varying gust properties show good agreement with those from previous experiments in moderately Complex Terrain but generate nonconservative estimates of the gust properties that are of key importance to structural loading. Probability distributions of gust magnitude derived from vertically pointing Doppler lidars exhibit good agreement with estimates from sonic anemometers despite differences arising from volumetric averaging and the Terrain Complexity. Wind speed coherence functions during gusty periods (which are important to structural wind loading) are similar to less Complex sites for small vertical displacements (10 to 40 m), but do not exhibit an exponential form for larger horizontal displacements (800 to 1500 m).
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modeling wake effects in large wind farms in Complex Terrain the problem the methods and the issues
Wind Energy, 2012Co-Authors: Evangelos S. Politis, P. K. Chaviaropoulos, John Prospathopoulos, Daniel Cabezon, Kurt Schaldemose Hansen, Rebecca Jane BarthelmieAbstract:Computational fluid dynamic (CFD) methods are used in this paper to predict the power production from entire wind farms in Complex Terrain and to shed some light into the wake flow patterns. Two full three-dimensional Navier–Stokes solvers for incompressible fluid flow, employing k − ϵ and k − ω turbulence closures, are used. The wind turbines are modeled as momentum absorbers by means of their thrust coefficient through the actuator disk approach. Alternative methods for estimating the reference wind speed in the calculation of the thrust are tested. The work presented in this paper is part of the work being undertaken within the UpWind Integrated Project that aims to develop the design tools for next generation of large wind turbines. In this part of UpWind, the performance of wind farm and wake models is being examined in Complex Terrain environment where there are few pre-existing relevant measurements. The focus of the work being carried out is to evaluate the performance of CFD models in large wind farm applications in Complex Terrain and to examine the development of the wakes in a Complex Terrain environment. Copyright © 2011 John Wiley & Sons, Ltd.
Barry A. Gardiner - One of the best experts on this subject based on the ideXlab platform.
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Modelling Canopy Flows over Complex Terrain
Boundary-Layer Meteorology, 2016Co-Authors: Eleanor R. Grant, Andrew N. Ross, Barry A. GardinerAbstract:Recent studies of flow over forested hills have been motivated by a number of important applications including understanding CO $$_2$$ 2 and other gaseous fluxes over forests in Complex Terrain, predicting wind damage to trees, and modelling wind energy potential at forested sites. Current modelling studies have focussed almost exclusively on highly idealized, and usually fully forested, hills. Here, we present model results for a site on the Isle of Arran, Scotland with Complex Terrain and heterogeneous forest canopy. The model uses an explicit representation of the canopy and a 1.5-order turbulence closure for flow within and above the canopy. The validity of the closure scheme is assessed using turbulence data from a field experiment before comparing predictions of the full model with field observations. For near-neutral stability, the results compare well with the observations, showing that such a relatively simple canopy model can accurately reproduce the flow patterns observed over Complex Terrain and realistic, variable forest cover, while at the same time remaining computationally feasible for real case studies. The model allows closer examination of the flow separation observed over Complex forested Terrain. Comparisons with model simulations using a roughness length parametrization show significant differences, particularly with respect to flow separation, highlighting the need to explicitly model the forest canopy if detailed predictions of near-surface flow around forests are required.
Kurt Schaldemose Hansen - One of the best experts on this subject based on the ideXlab platform.
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CFD modelling of wind farms in Complex Terrain
2020Co-Authors: John Prospathopoulos, Daniel Cabezón Martínez, P. K. Chaviaropoulos, K. Rados, J.g. Schepers, Kurt Schaldemose Hansen, Evangelos S. Politis, Rebecca Jane BarthelmieAbstract:Modelling of entire wind farms in flat and Complex Terrain using a full 3D Navier–Stokes solver for incompressible flow is presented in this paper. Numerical integration of the governing equations is performed using an implicit pressure correction scheme, where the wind turbines (W/Ts) are modelled as momentum absorbers through their thrust coefficient. The k–ω turbulence model, suitably modified for atmospheric flows, is employed for closure. A correction is introduced to account for the underestimation of the near wake deficit, in which the turbulence time scale is bounded using a general “realizability” constraint for the fluctuating velocities. The second modelling issue that is discussed in this paper is related to the determination of the reference wind speed for the thrust calculation of the machines. Dealing with large wind farms and wind farms in Complex Terrain, determining the reference wind speed is not obvious when a W/T operates in the wake of another WT and/or in Complex Terrain. Two alternatives are compared: using the wind speed value at hub height one diameter upstream of the W/T and adopting an induction factor-based concept to overcome the utilization of a wind speed at a certain distance upwind of the rotor. Application is made in two wind farms, a five-machine one located in flat Terrain and a 43-machine one located in Complex Terrain.
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Simulation of wind farms in flat and Complex Terrain using CFD
2020Co-Authors: John Prospathopoulos, Daniel Cabezón Martínez, P. K. Chaviaropoulos, K. Rados, J.g. Schepers, Kurt Schaldemose Hansen, Evangelos S. Politis, Rebecca Jane BarthelmieAbstract:Use of computational fluid dynamic (CFD) methods to predict the power production from wind entire wind farms in flat and Complex Terrain is presented in this paper. Two full 3D Navier–Stokes solvers for incompressible flow are employed that incorporate the k–e and k–ω turbulence models respectively. The wind turbines (W/Ts) are modelled as momentum absorbers by means of their thrust coefficient using the actuator disk approach. The WT thrust is estimated using the wind speed one diameter upstream of the rotor at hub height. An alternative method that employs an induction-factor based concept is also tested. This method features the advantage of not utilizing the wind speed at a specific distance from the rotor disk, which is a doubtful approximation when a W/T is located in the wake of another and/or the Terrain is Complex. To account for the underestimation of the near wake deficit, a correction is introduced to the turbulence model. The turbulence time scale is bounded using the general “realizability” constraint for the turbulent velocities. Application is made on two wind farms, a five-machine one located in flat Terrain and another 43-machine one located in Complex Terrain. In the flat Terrain case, the combination of the induction factor method along with the turbulence correction provides satisfactory results. In the Complex Terrain case, there are some significant discrepancies with the measurements, which are discussed. In this case, the induction factor method does not provide satisfactory results.
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Simulation of Wind Farms in Flat & Complex Terrain using CFD
2020Co-Authors: John Prospathopoulos, P. K. Chaviaropoulos, K. Rados, J.g. Schepers, Daniel Cabezon, Kurt Schaldemose Hansen, Evangelos S. Politis, Rebecca Jane BarthelmieAbstract:Use of computational fluid dynamic (CFD) methods to predict the power production from wind entire wind farms in flat and Complex Terrain is presented in this paper. Two full 3D Navier–Stokes solvers for incompressible flow are employed that incorporate the k–e and k–ω turbulence models respectively. The wind turbines (W/Ts) are modelled as momentum absorbers by means of their thrust coefficient using the actuator disk approach. The WT thrust is estimated using the wind speed one diameter upstream of the rotor at hub height. An alternative method that employs an induction-factor based concept is also tested. This method features the advantage of not utilizing the wind speed at a specific distance from the rotor disk, which is a doubtful approximation when a W/T is located in the wake of another and/or the Terrain is Complex. To account for the underestimation of the near wake deficit, a correction is introduced to the turbulence model. The turbulence time scale is bounded using the general “realizability” constraint for the turbulent velocities. Application is made on two wind farms, a five-machine one located in flat Terrain and another 43-machine one located in Complex Terrain. In the flat Terrain case, the combination of the induction factor method along with the turbulence correction provides satisfactory results. In the Complex Terrain case, there are some significant discrepancies with the measurements, which are discussed. In this case, the induction factor method does not provide satisfactory results.
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Wind turbine wake measurement in Complex Terrain
Journal of Physics: Conference Series, 2016Co-Authors: Kurt Schaldemose Hansen, Gunner Chr. Larsen, Robert Menke, Nikola Vasiljevic, Nikolas Angelou, Ju Feng, Andrea Vignaroli, Chang Xu, Wen Zhong ShenAbstract:SCADA data from a wind farm and high frequency time series measurements obtained with remote scanning systems have been analysed with focus on identification of wind turbine wake properties in Complex Terrain. The analysis indicates that within the flow regime characterized by medium to large downstream distances (more than 5 diameters) from the wake generating turbine, the wake changes according to local atmospheric conditions e.g. vertical wind speed. In very Complex Terrain the wake effects are often "overruled" by distortion effects due to the Terrain Complexity or topology.
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modeling wake effects in large wind farms in Complex Terrain the problem the methods and the issues
Wind Energy, 2012Co-Authors: Evangelos S. Politis, P. K. Chaviaropoulos, John Prospathopoulos, Daniel Cabezon, Kurt Schaldemose Hansen, Rebecca Jane BarthelmieAbstract:Computational fluid dynamic (CFD) methods are used in this paper to predict the power production from entire wind farms in Complex Terrain and to shed some light into the wake flow patterns. Two full three-dimensional Navier–Stokes solvers for incompressible fluid flow, employing k − ϵ and k − ω turbulence closures, are used. The wind turbines are modeled as momentum absorbers by means of their thrust coefficient through the actuator disk approach. Alternative methods for estimating the reference wind speed in the calculation of the thrust are tested. The work presented in this paper is part of the work being undertaken within the UpWind Integrated Project that aims to develop the design tools for next generation of large wind turbines. In this part of UpWind, the performance of wind farm and wake models is being examined in Complex Terrain environment where there are few pre-existing relevant measurements. The focus of the work being carried out is to evaluate the performance of CFD models in large wind farm applications in Complex Terrain and to examine the development of the wakes in a Complex Terrain environment. Copyright © 2011 John Wiley & Sons, Ltd.
Eric Kutter - One of the best experts on this subject based on the ideXlab platform.
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Stably stratified canopy flow in Complex Terrain
Atmospheric Chemistry and Physics, 2014Co-Authors: Xiyan Xu, Chuixiang Yi, Eric KutterAbstract:Stably stratified canopy flow in Complex Terrain has been considered a difficult condition for measuring net ecosystem-atmosphere exchanges of carbon, water vapor, and energy. A long-standing advection error in eddy-flux measurements is caused by stably stratified canopy flow. Such a condition with strong thermal gradient and less tur- bulent air is also difficult for modeling. To understand the challenging atmospheric condition for eddy-flux measure- ments, we use the renormalized group (RNG) k-" turbu- lence model to investigate the main characteristics of sta- bly stratified canopy flows in Complex Terrain. In this two- dimensional simulation, we imposed persistent constant heat flux at ground surface and linearly increasing cooling rate in the upper-canopy layer, vertically varying dissipative force from canopy drag elements, buoyancy forcing induced from thermal stratification and the hill Terrain. These strong bound- ary effects keep nonlinearity in the two-dimensional Navier- Stokes equations high enough to generate turbulent behav- ior. The fundamental characteristics of nighttime canopy flow over Complex Terrain measured by the small number of available multi-tower advection experiments can be re- produced by this numerical simulation, such as (1) unstable layer in the canopy and super-stable layers associated with flow decoupling in deep canopy and near the top of canopy; (2) sub-canopy drainage flow and drainage flow near the top of canopy in calm night; (3) upward momentum transfer in canopy, downward heat transfer in upper canopy and upward heat transfer in deep canopy; and (4) large buoyancy suppres- sion and weak shear production in strong stability.
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Stably stratified canopy flow in Complex Terrain
Atmospheric Chemistry and Physics Discussions, 2014Co-Authors: Xiyan Xu, Chuixiang Yi, Eric KutterAbstract:Abstract. The characteristics of stably stratified canopy flows in Complex Terrain are investigated by employing the Renormalized Group (RNG) k-ε turbulence model. In this two-dimensional simulation, we imposed persistent constant heat flux at ground surface and linearly increasing cooling rate in the upper canopy layer, vertically varying dissipative force from canopy drag elements, buoyancy forcing induced from thermal stratification and the hill Terrain. These strong boundary effects keep nonlinearity in the two-dimensional Navier–Stokes equations high enough to generate turbulent behavior. The fundamental characteristics of nighttime canopy flow over Complex Terrain measured by a few multi-tower advection experiments can be produced by this numerical simulation, such as: (1) unstable layer in the canopy, (2) super-stable layer associated with flow decoupling in deep canopy and near the top of canopy, (3) upward momentum transfer in canopy, and (4) large buoyancy suppression and weak shear production in strong stability.
Evangelos S. Politis - One of the best experts on this subject based on the ideXlab platform.
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CFD modelling of wind farms in Complex Terrain
2020Co-Authors: John Prospathopoulos, Daniel Cabezón Martínez, P. K. Chaviaropoulos, K. Rados, J.g. Schepers, Kurt Schaldemose Hansen, Evangelos S. Politis, Rebecca Jane BarthelmieAbstract:Modelling of entire wind farms in flat and Complex Terrain using a full 3D Navier–Stokes solver for incompressible flow is presented in this paper. Numerical integration of the governing equations is performed using an implicit pressure correction scheme, where the wind turbines (W/Ts) are modelled as momentum absorbers through their thrust coefficient. The k–ω turbulence model, suitably modified for atmospheric flows, is employed for closure. A correction is introduced to account for the underestimation of the near wake deficit, in which the turbulence time scale is bounded using a general “realizability” constraint for the fluctuating velocities. The second modelling issue that is discussed in this paper is related to the determination of the reference wind speed for the thrust calculation of the machines. Dealing with large wind farms and wind farms in Complex Terrain, determining the reference wind speed is not obvious when a W/T operates in the wake of another WT and/or in Complex Terrain. Two alternatives are compared: using the wind speed value at hub height one diameter upstream of the W/T and adopting an induction factor-based concept to overcome the utilization of a wind speed at a certain distance upwind of the rotor. Application is made in two wind farms, a five-machine one located in flat Terrain and a 43-machine one located in Complex Terrain.
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Simulation of wind farms in flat and Complex Terrain using CFD
2020Co-Authors: John Prospathopoulos, Daniel Cabezón Martínez, P. K. Chaviaropoulos, K. Rados, J.g. Schepers, Kurt Schaldemose Hansen, Evangelos S. Politis, Rebecca Jane BarthelmieAbstract:Use of computational fluid dynamic (CFD) methods to predict the power production from wind entire wind farms in flat and Complex Terrain is presented in this paper. Two full 3D Navier–Stokes solvers for incompressible flow are employed that incorporate the k–e and k–ω turbulence models respectively. The wind turbines (W/Ts) are modelled as momentum absorbers by means of their thrust coefficient using the actuator disk approach. The WT thrust is estimated using the wind speed one diameter upstream of the rotor at hub height. An alternative method that employs an induction-factor based concept is also tested. This method features the advantage of not utilizing the wind speed at a specific distance from the rotor disk, which is a doubtful approximation when a W/T is located in the wake of another and/or the Terrain is Complex. To account for the underestimation of the near wake deficit, a correction is introduced to the turbulence model. The turbulence time scale is bounded using the general “realizability” constraint for the turbulent velocities. Application is made on two wind farms, a five-machine one located in flat Terrain and another 43-machine one located in Complex Terrain. In the flat Terrain case, the combination of the induction factor method along with the turbulence correction provides satisfactory results. In the Complex Terrain case, there are some significant discrepancies with the measurements, which are discussed. In this case, the induction factor method does not provide satisfactory results.
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Simulation of Wind Farms in Flat & Complex Terrain using CFD
2020Co-Authors: John Prospathopoulos, P. K. Chaviaropoulos, K. Rados, J.g. Schepers, Daniel Cabezon, Kurt Schaldemose Hansen, Evangelos S. Politis, Rebecca Jane BarthelmieAbstract:Use of computational fluid dynamic (CFD) methods to predict the power production from wind entire wind farms in flat and Complex Terrain is presented in this paper. Two full 3D Navier–Stokes solvers for incompressible flow are employed that incorporate the k–e and k–ω turbulence models respectively. The wind turbines (W/Ts) are modelled as momentum absorbers by means of their thrust coefficient using the actuator disk approach. The WT thrust is estimated using the wind speed one diameter upstream of the rotor at hub height. An alternative method that employs an induction-factor based concept is also tested. This method features the advantage of not utilizing the wind speed at a specific distance from the rotor disk, which is a doubtful approximation when a W/T is located in the wake of another and/or the Terrain is Complex. To account for the underestimation of the near wake deficit, a correction is introduced to the turbulence model. The turbulence time scale is bounded using the general “realizability” constraint for the turbulent velocities. Application is made on two wind farms, a five-machine one located in flat Terrain and another 43-machine one located in Complex Terrain. In the flat Terrain case, the combination of the induction factor method along with the turbulence correction provides satisfactory results. In the Complex Terrain case, there are some significant discrepancies with the measurements, which are discussed. In this case, the induction factor method does not provide satisfactory results.
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modeling wake effects in large wind farms in Complex Terrain the problem the methods and the issues
Wind Energy, 2012Co-Authors: Evangelos S. Politis, P. K. Chaviaropoulos, John Prospathopoulos, Daniel Cabezon, Kurt Schaldemose Hansen, Rebecca Jane BarthelmieAbstract:Computational fluid dynamic (CFD) methods are used in this paper to predict the power production from entire wind farms in Complex Terrain and to shed some light into the wake flow patterns. Two full three-dimensional Navier–Stokes solvers for incompressible fluid flow, employing k − ϵ and k − ω turbulence closures, are used. The wind turbines are modeled as momentum absorbers by means of their thrust coefficient through the actuator disk approach. Alternative methods for estimating the reference wind speed in the calculation of the thrust are tested. The work presented in this paper is part of the work being undertaken within the UpWind Integrated Project that aims to develop the design tools for next generation of large wind turbines. In this part of UpWind, the performance of wind farm and wake models is being examined in Complex Terrain environment where there are few pre-existing relevant measurements. The focus of the work being carried out is to evaluate the performance of CFD models in large wind farm applications in Complex Terrain and to examine the development of the wakes in a Complex Terrain environment. Copyright © 2011 John Wiley & Sons, Ltd.