Large-Eddy Simulation of Stably-Stratified Flow Over a Steep Hill

Feng, Wen-hai; Porté‐Agel, Fernando

doi:10.1007/s10546-010-9562-4

Cited by 48 publications

(37 citation statements)

References 36 publications

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“…This inflow condition was generated from a separate precursor simulation of boundary layer flow for a no-turbine case, after having ensured that the flow had attained statistical stationarity. This method of using a buffer zone to impose the inflow boundary conditions without loss of accuracy of the pseudospectral LES codes, has been successfully employed in a number of studies, such as turbulent flow over urban canopies [54], flow over steep hills [55], and flow through stand alone wind turbines, as well as wind farms [38,41,[56][57][58].…”

Section: Computational Setupmentioning

confidence: 99%

Wind Turbine Wake Mitigation through Blade Pitch Offset

Dilip

Porté‐Agel

2017

Energies

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Abstract:The reduction in power output associated with complex turbine-wake interactions in wind farms necessitates the development of effective wake mitigation strategies. One approach to this end entails the downregulation of individual turbines from its maximum power point with the objective of optimizing the overall wind farm productivity. Downregulation via blade pitch offset has been of interest as a potential strategy, though the viability of this method is still not clear, especially in regard to its sensitivity to ambient turbulence. In this study, large-eddy simulations of a two-turbine arrangement, with the second turbine in the full wake of the first, were performed. The effects of varying the blade pitch angle of the upstream turbine on its wake characteristics, as well as the combined power of the two, were investigated. Of specific interest was the effect of turbulence intensity of the inflow on the efficacy of this method. Results showed enhanced wake recovery associated with pitching to stall, as opposed to pitching to feather, which delayed wake recovery. The increased wake recovery resulted in a noticeable increase in the power of the two-turbine configuration, only in conditions characterized by low turbulence in the incoming flow. Nevertheless, the low turbulence scenarios where the use of this method is favorable, are expected in realistic wind farms, suggesting its possible application for improved power generation.

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Section: Computational Setupmentioning

confidence: 99%

Wind Turbine Wake Mitigation through Blade Pitch Offset

Dilip

Porté‐Agel

2017

Energies

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“…The inflow conditions are obtained from separate simulations of fully-developed neutral ABL flows over horizontally-homogeneous flat surfaces with the four different roughness lengths considered here. More details regarding the separate inflow simulations are discussed in Section 2.2 The use of a similar buffer region to impose the inflow boundary condition while maintaining the accuracy of pseudospectral LES codes has been successful in former studies of turbulent transport in urban street canopies [39], flow over a steep hill [40], flow through a stand-alone wind turbine [8,20], and flows over both aligned and staggered wind farms [22]. Table 1.…”

Section: Les Framework and Set-upmentioning

confidence: 99%

Atmospheric Turbulence Effects on Wind-Turbine Wakes: An LES Study

2012

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A numerical study of atmospheric turbulence effects on wind-turbine wakes is presented. Large-eddy simulations of neutrally-stratified atmospheric boundary layer flows through stand-alone wind turbines were performed over homogeneous flat surfaces with four different aerodynamic roughness lengths. Emphasis is placed on the structure and characteristics of turbine wakes in the cases where the incident flows to the turbine have the same mean velocity at the hub height but different mean wind shears and turbulence intensity levels. The simulation results show that the different turbulence intensity levels of the incoming flow lead to considerable influence on the spatial distribution of the mean velocity deficit, turbulence intensity, and turbulent shear stress in the wake region. In particular, when the turbulence intensity level of the incoming flow is higher, the turbine-induced wake (velocity deficit) recovers faster, and the locations of the maximum turbulence intensity and turbulent stress are closer to the turbine. A detailed analysis of the turbulence kinetic energy budget in the wakes reveals also an important effect of the incoming flow turbulence level on the magnitude and spatial distribution of the shear production and transport terms.

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“…More details on the formulation of scale-dependent dynamic models for the SGS stress and the SGS scalar fluxes can be found in Porté-Agel et al [18], Porté-Agel [19] and Stoll and Porté-Agel [13]. The scale-dependent Lagrangian dynamic model has been successfully applied to neutral homogeneous and heterogeneous ABLs [13,20], to the homogeneous stable boundary layer (SBL) [21], to boundary-layer flow over topography [22,23] and boundary-layer flow through the wind farm [4,24].…”

Section: Les Governing Equationsmentioning

confidence: 99%

The Effect of Free-Atmosphere Stratification on Boundary-Layer Flow and Power Output from Very Large Wind Farms

2013

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Large-eddy simulation is used to study the influence of free-atmosphere stratification on the structure of atmospheric boundary-layer flow inside and above very large wind farms, as well as the power extracted by the wind turbines. In the simulations, tuning-free Lagrangian scale-dependent dynamic models are used to model the subgrid-scale turbulent fluxes, while the turbine-induced forces are parameterized with an actuator-disk model. It is shown that for a given surface cover (with and without turbines) thermal stratification of the free atmosphere reduces the entrainment from the flow above compared with the unstratified case, leading to lower boundary-layer depth. Due to the fact that in very large wind farms vertical energy transport associated with turbulence is the only source of kinetic energy, lower entrainment leads to lower power production by the wind turbines. In particular, for the wind-turbine arrangements considered in the present work, the power output from the wind farms is reduced by about 35% when the potential temperature lapse rate in the free atmosphere increases from 1 to 10 K/km (within the range of values typically observed in the atmosphere). Moreover, it is shown that the presence of the turbines has significant effect on the growth of the boundary layer. Inspired by the obtained results, a simple one-dimensional model is developed to account for the effect of free-atmosphere stability on the mean flow and the power output from very large wind farms.

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Large-Eddy Simulation of Stably-Stratified Flow Over a Steep Hill

Cited by 48 publications

References 36 publications

Wind Turbine Wake Mitigation through Blade Pitch Offset

Wind Turbine Wake Mitigation through Blade Pitch Offset

Atmospheric Turbulence Effects on Wind-Turbine Wakes: An LES Study

The Effect of Free-Atmosphere Stratification on Boundary-Layer Flow and Power Output from Very Large Wind Farms

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