scholarly journals Near-wake analysis of actuator line method immersed in turbulent flow using large-eddy simulations

2018 ◽  
Vol 3 (2) ◽  
pp. 905-917 ◽  
Author(s):  
Jörn Nathan ◽  
Christian Masson ◽  
Louis Dufresne
Keyword(s):  
Model Experiment ◽  
Wind Farm ◽  
Isotropic Turbulence ◽  
Large Eddy Simulations ◽  
Energy Output ◽  
Near Wake ◽  
Controlled Conditions ◽  
Large Eddy ◽  
Distribution Kernel ◽  
Ambient Turbulence

Abstract. The interaction between wind turbines through their wakes is an important aspect of the conception and operation of a wind farm. Wakes are characterized by an elevated turbulence level and a noticeable velocity deficit, which causes a decrease in energy output and fatigue on downstream turbines. In order to gain a better understanding of this phenomenon this work uses large-eddy simulations together with an actuator line model and different ambient turbulence imposed as boundary conditions. This is achieved by using the Simulator fOr Wind Farm Applications (SOWFA) framework from the National Renewable Energy Laboratory (NREL) (USA), which is first validated against another popular Computational Fluid Dynamics (CFD) framework for wind energy, EllipSys3D, and then verified against the experimental results from the Model Experiment in Controlled Conditions (MEXICO) and New Model Experiment in Controlled Conditions (NEW MEXICO) wind tunnel experiments. By using the predicted torque as a global indicator, the optimal width of the distribution kernel for the actuator line is determined for different grid resolutions. Then, the rotor is immersed in homogeneous isotropic turbulence and a shear layer turbulence with different turbulence intensities, allowing us to determine how far downstream the effect of the distinct blades is discernible. This can be used as an indicator of the extents of the near wake for different flow conditions.

scholarly journals Near wake analysis of actuator line method immersed in turbulent flow using large-eddy simulations

2018 ◽  
Author(s):  
Jörn Nathan ◽  
Christian Masson ◽  
Louis Dufresne
Keyword(s):  
Wind Farm ◽  
Isotropic Turbulence ◽  
Large Eddy Simulations ◽  
Energy Output ◽  
Flow Conditions ◽  
Wind Tunnel Experiments ◽  
Near Wake ◽  
Large Eddy ◽  
Distribution Kernel ◽  
Global Indicator

Abstract. The interaction between wind turbines through their wakes is an important aspect of the conception and operation of a wind farm. Wakes are characterized by an elevated turbulence level and a noticable velocity deficit which causes a decrease in energy output and fatigue on downstream turbines. In order to gain a better understanding of this phenomenon this works uses large-eddy simulations together with an actuator line model and different ambient turbulences imposed as boundary conditions. This is achieved by using the SOWFA framework from NREL (USA) which is first validated against another popular CFD framework for wind energy, EllipSys3D, and then verified against the experimental results from the MEXICO and NEW MEXICO wind tunnel experiments. By using the predicted torque as a global indicator, the optimal width of the distribution kernel for the actuator line is determined for different grid resolutions. Then the rotor is immersed in homogeneous isotropic turbulence and a shear layer turbulence with different turbulence intensities, allowing to determine how far downstream the effect of the distinct blades is discernible. This can be used as an indicator for the extents of the near wake for different flow conditions

scholarly journals Statistical ensemble of large-eddy simulations

2002 ◽  
Vol 455 ◽  
pp. 195-212 ◽  
Author(s):  
DANIELE CARATI ◽  
MICHAEL M. ROGERS ◽  
ALAN A. WRAY
Keyword(s):  
Large Scale ◽  
Isotropic Turbulence ◽  
Velocity Fields ◽  
Large Eddy Simulations ◽  
Statistical Ensemble ◽  
Model Parameters ◽  
Spatial Averaging ◽  
Subgrid Scale ◽  
Large Eddy ◽  
New Models

A statistical ensemble of large-eddy simulations (LES) is run simultaneously for the same flow. The information provided by the different large-scale velocity fields is used in an ensemble-averaged version of the dynamic model. This produces local model parameters that only depend on the statistical properties of the flow. An important property of the ensemble-averaged dynamic procedure is that it does not require any spatial averaging and can thus be used in fully inhomogeneous flows. Also, the ensemble of LES provides statistics of the large-scale velocity that can be used for building new models for the subgrid-scale stress tensor. The ensemble-averaged dynamic procedure has been implemented with various models for three flows: decaying isotropic turbulence, forced isotropic turbulence, and the time-developing plane wake. It is found that the results are almost independent of the number of LES in the statistical ensemble provided that the ensemble contains at least 16 realizations.

scholarly journals Wake behavior and control: comparison of LES simulations and wind tunnel measurements

2019 ◽  
Vol 4 (1) ◽  
pp. 71-88 ◽  
Author(s):  
Jiangang Wang ◽  
Chengyu Wang ◽  
Filippo Campagnolo ◽  
Carlo L. Bottasso
Keyword(s):  
Wind Tunnel ◽  
Wind Turbine ◽  
Wind Farm ◽  
Operating Conditions ◽  
Test Cases ◽  
Near Wake ◽  
Large Eddy ◽  
Control Comparison ◽  
High Turbulence ◽  
And Control

Abstract. This paper applies a large-eddy actuator line approach to the simulation of wind turbine wakes. In addition to normal operating conditions, a specific focus of the paper is on wake manipulation, which is performed here by derating, yaw misalignment and cyclic pitching of the blades. With the purpose of clarifying the ability of LES methods to represent conditions that are relevant for wind farm control, numerical simulations are compared to experimental observations obtained in a boundary layer wind tunnel with scaled wind turbine models. Results indicate a good overall matching of simulations with experiments. Low-turbulence test cases appear to be more challenging than moderate- and high-turbulence ones due to the need for denser grids to limit numerical diffusion and accurately resolve tip-shed vortices in the near-wake region.

scholarly journals The Aerodynamics of the Curled Wake: A Simplified Model in View of Flow Control

2018 ◽  
Author(s):  
Luis A. Martínez-Tossas ◽  
Jennifer Annoni ◽  
Paul A. Fleming ◽  
Matthew J. Churchfield
Keyword(s):  
Boundary Layer ◽  
Steady State ◽  
Wind Farm ◽  
Stokes Equations ◽  
Large Eddy Simulations ◽  
Simplified Model ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Actuator Disk ◽  
Large Eddy

Abstract. When a wind turbine is yawed, the shape of the wake changes and a curled wake profile is generated. The curled wake has drawn a lot of interest because of its aerodynamic complexity and applicability to wind farm controls. The main mechanism for the creation of the curled wake has been identified in the literature as a collection of vortices that are shed from the rotor plane when the turbine is yawed. This work extends that idea by using aerodynamic concepts to develop a control-oriented model for the curled wake based on approximations to the Navier-Stokes equations. The model is tested and compared to large-eddy simulations using actuator disk and line models. The model is able to capture the curling mechanism for a turbine under uniform inflow and in the case of a neutral atmospheric boundary layer. The model is then tested inside the FLOw Redirection and Induction in Steady State framework and provides excellent agreement with power predictions for cases with two and three turbines in a row.

scholarly journals Evaluation of the the wind farm wake parametrization with large-eddy simulations of wakes in WRF

2021 ◽  
Author(s):  
Alfredo Peña ◽  
Jeffrey Mirocha
Keyword(s):  
Boundary Layer ◽  
Wind Farm ◽  
Wrf Model ◽  
Wind Farms ◽  
Large Eddy Simulations ◽  
Disk Model ◽  
Mesoscale Models ◽  
Boundary Layer Height ◽  
Wind Speeds ◽  
Large Eddy

<p>Mesoscale models, such as the Weather Research and Forecasting (WRF) model, are now commonly used to predict wind resources, and in recent years their outputs are being used as inputs to wake models for the prediction of the production of wind farms. Also, wind farm parametrizations have been implemented in the mesoscale models but their accuracy to reproduce wind speeds and turbulent kinetic energy fields within and around wind farms is yet unknown. This is partly because they have been evaluated against wind farm power measurements directly and, generally, a lack of high-quality observations of the wind field around large wind farms. Here, we evaluate the in-built wind farm parametrization of the WRF model, the so-called Fitch scheme that works together with the MYNN2 planetary boundary layer (PBL) scheme against large-eddy simulations (LES) of wakes using a generalized actuator disk model, which was also implemented within the same WRF version. After setting both types of simulations as similar as possible so that the inflow conditions are nearly identical, preliminary results show that the velocity deficits can differ up to 50% within the same area (determined by the resolution of the mesoscale run) where the turbine is placed. In contrast, within that same area, the turbine-generated TKE is nearly identical in both simulations. We also prepare an analysis of the sensitivity of the results to the inflow wind conditions, horizontal grid resolution of both the LES and the PBL run, number of turbines within the mesoscale grid cells, surface roughness, inversion strength, and boundary-layer height.</p>

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