scholarly journals A large-eddy simulation study of wake propagation and power production in an array of tidal-current turbines

2013 ◽  
Vol 371 (1985) ◽  
pp. 20120421 ◽  
Author(s):  
Matthew J. Churchfield ◽  
Ye Li ◽  
Patrick J. Moriarty
Keyword(s):  
Power Production ◽  
Vertical Shear ◽  
Total Power ◽  
Turbulent Structures ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Tidal Turbine ◽  
Initial Work ◽  
Small Benefit ◽  
Volume Method

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 those data are used as inflow into a tidal turbine array two rows deep and infinitely wide. The turbines are modelled 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. We found that 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. For example, using a larger precursor domain would better capture elongated turbulent structures, and including salinity and temperature equations would account for density stratification and its effect on turbulence. Additionally, the wall shear stress modelling could be improved, and more array configurations could be examined.

LES of Airflow Distribution for CRH2 Electric Motor Train Units

2014 ◽  
Vol 687-691 ◽  
pp. 109-112
Author(s):  
Zhong Zan Wang ◽  
Zhao Hui Qi ◽  
Hui Tian
Keyword(s):  
Electric Motor ◽  
High Speed ◽  
Wall Functions ◽  
Eddy Simulation ◽  
Airflow Distribution ◽  
Large Eddy ◽  
Model Coefficient ◽  
Set Up ◽  
Volume Method ◽  
Temperature And Velocity Fields

In the premise of parallel computing, large eddy simulation (LES) model was adopted to set up math formers for the characteristics of airflow origination in CRH2 Electric Motor Train Units(EMU) in this paper. The Smagorinsky-Lilly dynamic sub-grid model was adopted for fitting local turbulent structure and confirming benchmark model coefficient. Amended balance layer model was used to the wall functions. The temperature and velocity fields in the compartments were numerically simulated. Furthermore, area discretization adopted finite volume method. The results showed, adopting the method of enlarging calculation region, the instantaneous and continuity of turbulence were reflected truly and accurately. The analysis provided a reference for LES of airflow organization in high-speed train. It was also a new reference for the evaluation of comfort environment in the train.

scholarly journals Atmospheric Stability Influences on Coupled Boundary Layer and Canopy Turbulence

2016 ◽  
Vol 73 (4) ◽  
pp. 1621-1647 ◽  
Author(s):  
Edward G. Patton ◽  
Peter P. Sullivan ◽  
Roger H. Shaw ◽  
John J. Finnigan ◽  
Jeffrey C. Weil
Keyword(s):  
Boundary Layer ◽  
Atmospheric Stability ◽  
Canopy Turbulence ◽  
Vertical Shear ◽  
Horizontal Wind ◽  
Atmospheric Boundary Layers ◽  
Eddy Simulation ◽  
Scalar Fluxes ◽  
Large Eddy ◽  
Scale Structures

Abstract Large-eddy simulation of atmospheric boundary layers interacting with a coupled and resolved plant canopy reveals the influence of atmospheric stability variations from neutral to free convection on canopy turbulence. The design and implementation of a new multilevel canopy model is presented. Instantaneous fields from the simulations show that organized motions on the scale of the atmospheric boundary layer (ABL) depth bring high momentum down to canopy top, locally modulating the vertical shear of the horizontal wind. The evolution of these ABL-scale structures with increasing instability and their impact on vertical profiles of turbulence moments and integral length scales within and above the canopy are discussed. Linkages between atmospheric turbulence and biological control impact horizontal scalar source distributions. Decreasing spatial correlation between momentum and scalar fluxes with increasing instability results from ABL-scale structures spatially segregating momentum and scalar exchange at canopy top. In combination, these results suggest the need for roughness sublayer parameterizations to incorporate an additional length or time scale reflecting the influence of ABL-scale organized motions.

scholarly journals The Collection Efficiency of Shielded and Unshielded Precipitation Gauges. Part II: Modeling Particle Trajectories

2015 ◽  
Vol 17 (1) ◽  
pp. 245-255 ◽  
Author(s):  
Matteo Colli ◽  
Luca G. Lanza ◽  
Roy Rasmussen ◽  
Julie M. Thériault
Keyword(s):  
Collection Efficiency ◽  
Time Dependent ◽  
Navier Stokes ◽  
Turbulent Structures ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Efficiency Comparison ◽  
The One ◽  
The Impact

Abstract The use of windshields to reduce the impact of wind on snow measurements is common. This paper investigates the catching performance of shielded and unshielded gauges using numerical simulations. In Part II, the role of the windshield and gauge aerodynamics, as well as the varying flow field due to the turbulence generated by the shield–gauge configuration, in reducing the catch efficiency is investigated. This builds on the computational fluid dynamics results obtained in Part I, where the airflow patterns in the proximity of an unshielded and single Alter shielded Geonor T-200B gauge are obtained using both time-independent [Reynolds-averaged Navier–Stokes (RANS)] and time-dependent [large-eddy simulation (LES)] approaches. A Lagrangian trajectory model is used to track different types of snowflakes (wet and dry snow) and to assess the variation of the resulting gauge catching performance with the wind speed. The collection efficiency obtained with the LES approach is generally lower than the one obtained with the RANS approach. This is because of the impact of the LES-resolved turbulence above the gauge orifice rim. The comparison between the collection efficiency values obtained in case of shielded and unshielded gauge validates the choice of installing a single Alter shield in a windy environment. However, time-dependent simulations show that the propagating turbulent structures produced by the aerodynamic response of the upwind single Alter blades have an impact on the collection efficiency. Comparison with field observations provides the validation background for the model results.

Modelling the wake of a tidal turbine with upstream turbulence

2020 ◽  
Vol 3 (2) ◽  
pp. 83-89
Author(s):  
Mikaël Grondeau ◽  
Jean-Charles Poirier ◽  
Sylvain Guillou ◽  
Yann M´ear ◽  
Philippe Mercier ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Lattice Boltzmann ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Tidal Turbines ◽  
Large Eddy ◽  
Tidal Turbine ◽  
Good Concordance ◽  
Ambient Turbulence ◽  
Boltzmann Method

Tidal turbines are entering an industrial phase and farms will soon be installed. In order to optimize the power output of tidal farms, a good understanding of the interactions between the ambient turbulence and a single turbine is crucial. Computational Fluid Dynamics, and more precisely Large Eddy Simulation, is one way of acquiring such knowledge. This study proposed a comparison between a Lattice Boltzmann Method LES approach and a Navier-Stokes LES approach to model the wake of a tidal turbine. Numerical results are compared with experimental results and a relatively good concordance is observed. Differences inherent to the approaches are then pointed out.

Turbulence and Vertical Fluxes in the Stable Atmospheric Boundary Layer. Part I: A Large-Eddy Simulation Study

2013 ◽  
Vol 70 (6) ◽  
pp. 1513-1527 ◽  
Author(s):  
Jing Huang ◽  
Elie Bou-Zeid
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Atmospheric Boundary Layer ◽  
Length Scale ◽  
Quasi Equilibrium ◽  
Turbulent Structures ◽  
Constant Length ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Stable Atmospheric Boundary Layer

Abstract This study seeks to quantitatively and qualitatively understand how stability affects transport in the continuously turbulent stably stratified atmospheric boundary layer, based on a suite of large-eddy simulations. The test cases are based on the one adopted by the Global Energy and Water Cycle Experiment (GEWEX) Atmospheric Boundary Layer Study (GABLS) project, but with a largely expanded stability range where the gradient Richardson number (Rig) reaches up to around 1. The analysis is mainly focused on understanding the modification of turbulent structures and dynamics with increasing stability in order to improve the modeling of the stable atmospheric boundary layer in weather and climate models, a topic addressed in Part II of this work. It is found that at quasi equilibrium, an increase in stability results in stronger vertical gradients of the mean temperature, a lowered low-level jet, a decrease in vertical momentum transport, an increase in vertical buoyancy flux, and a shallower boundary layer. Analysis of coherent turbulent structures using two-point autocorrelation reveals that the autocorrelation of the streamwise velocity is horizontally anisotropic while the autocorrelation of the vertical velocity is relatively isotropic in the horizontal plane and its integral length scale decreases as stability increases. The effects of stability on the overall turbulent kinetic energy (TKE) and its budget terms are also investigated, and it is shown that the authors' large-eddy simulation results are in good agreement with previous experimental findings across varied stabilities. Finally, Nieuwstadt's local-scaling theory is reexamined and it is concluded that the height z is not a relevant scaling parameter and should be replaced by a constant length scale away from the surface, indicating that the z-less range starts lower than previously assumed.

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