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Fernando Porteagel - One of the best experts on this subject based on the ideXlab platform.
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a wind tunnel investigation of wind turbine wakes Boundary Layer Turbulence effects
Boundary-Layer Meteorology, 2009Co-Authors: Leonardo P Chamorro, Fernando PorteagelAbstract:Wind-tunnel experiments were performed to study Turbulence in the wake of a model wind turbine placed in a Boundary Layer developed over rough and smooth surfaces. Hot-wire anemometry was used to characterize the cross-sectional distribution of mean velocity, Turbulence intensity and kinematic shear stress at different locations downwind of the turbine for both surface roughness cases. Special emphasis was placed on the spatial distribution of the velocity deficit and the Turbulence intensity, which are important factors affecting turbine power generation and fatigue loads in wind energy parks. Non-axisymmetric behaviour of the wake is observed over both roughness types in response to the non-uniform incoming Boundary-Layer flow and the effect of the surface. Nonetheless, the velocity deficit with respect to the incoming velocity profile is nearly axisymmetric, except near the ground in the far wake where the wake interacts with the surface. It is found that the wind turbine induces a large enhancement of Turbulence levels (positive added Turbulence intensity) in the upper part of the wake. This is due to the effect of relatively large velocity fluctuations associated with helicoidal tip vortices near the wake edge, where the mean shear is strong. In the lower part of the wake, the mean shear and Turbulence intensity are reduced with respect to the incoming flow. The non-axisymmetry of the Turbulence intensity distribution of the wake is found to be stronger over the rough surface, where the incoming flow is less uniform at the turbine level. In the far wake the added turbulent intensity, its positive and negative contributions and its local maximum decay as a power law of downwind distance (with an exponent ranging from −0.3 to −0.5 for the rough surface, and with a wider variation for the smooth surface). Nevertheless, the effect of the turbine on the velocity defect and added Turbulence intensity is not negligible even in the very far wake, at a distance of fifteen times the rotor diameter.
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large eddy simulation of stably stratified atmospheric Boundary Layer Turbulence a scale dependent dynamic modeling approach
Journal of the Atmospheric Sciences, 2006Co-Authors: Sukanta Basu, Fernando PorteagelAbstract:Abstract A new tuning-free subgrid-scale model, termed locally averaged scale-dependent dynamic (LASDD) model, is developed and implemented in large-eddy simulations (LES) of stable Boundary Layers. The new model dynamically computes the Smagorinsky coefficient and the subgrid-scale Prandtl number based on the local dynamics of the resolved velocity and temperature fields. Overall, the agreement between the statistics of the LES-generated Turbulence and some well-established empirical formulations and theoretical predictions (e.g., the local scaling hypothesis) is remarkable. Moreover, the simulated statistics obtained with the LASDD model show relatively little resolution dependence for the range of grid sizes considered here. In essence, it is shown here that the new LASDD model is a robust subgrid-scale parameterization for reliable, tuning-free simulations of stable Boundary Layers, even with relatively coarse resolutions.
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revisiting the local scaling hypothesis in stably stratified atmospheric Boundary Layer Turbulence an integration of field and laboratory measurements with large eddy simulations
arXiv: Atmospheric and Oceanic Physics, 2005Co-Authors: Sukanta Basu, Jean-françois Vinuesa, Fernando Porteagel, Efi Foufoulageorgiou, Markus PahlowAbstract:The `local scaling' hypothesis, first introduced by Nieuwstadt two decades ago, describes the Turbulence structure of stable Boundary Layers in a very succinct way and is an integral part of numerous local closure-based numerical weather prediction models. However, the validity of this hypothesis under very stable conditions is a subject of on-going debate. In this work, we attempt to address this controversial issue by performing extensive analyses of Turbulence data from several field campaigns, wind-tunnel experiments and large-eddy simulations. Wide range of stabilities, diverse field conditions and a comprehensive set of Turbulence statistics make this study distinct.
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large eddy simulation of stably stratified atmospheric Boundary Layer Turbulence a scale dependent dynamic modeling approach
arXiv: Atmospheric and Oceanic Physics, 2005Co-Authors: Sukanta Basu, Fernando PorteagelAbstract:A new tuning-free subgrid-scale model, termed `locally-averaged scale-dependent dynamic' (LASDD) model, is developed and implemented in large-eddy simulations (LESs) of stable Boundary Layers. The new model dynamically computes the Smagorinsky coefficient and the subgrid-scale Prandtl number based on the local dynamics of the resolved velocity and temperature fields. Overall, the agreement between the statistics of the LES-generated Turbulence and some well-established empirical formulations and theoretical predictions (e.g., Nieuwstadt's local scaling hypothesis) is remarkable. The results show clear improvements over most of the traditional subgrid-scale models in the surface Layer. Moreover, in contrast to previous large-eddy simulations of stable Boundary Layers that have strong dependence on grid resolution, the simulated statistics obtained with the LASDD model show relatively little resolution dependence for the range of grid sizes considered here. In essence, we show that the new LASDD model is a robust subgrid-scale parameterization for reliable, tuning-free simulations of stable Boundary Layers, even with relatively coarse resolutions.
Sukanta Basu - One of the best experts on this subject based on the ideXlab platform.
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large eddy simulation of stable Boundary Layer Turbulence and estimation of associated wind turbine loads
Wind Energy, 2014Co-Authors: Jinkyoo Park, Sukanta Basu, Lance ManuelAbstract:Stochastic simulation of turbulent inflow fields commonly used in wind turbine load computations is unable to account for contrasting states of atmospheric stability. Flow fields in the stable Boundary Layer, for instance, have characteristics such as enhanced wind speed and directional shear; these effects can influence loads on utility-scale wind turbines. To investigate these influences, we use large-eddy simulation (LES) to generate an extensive database of high-resolution ( ∼ 10 m), four-dimensional turbulent flow fields. Key atmospheric conditions (e.g., geostrophic wind) and surface conditions (e.g., aerodynamic roughness length) are systematically varied to generate a diverse range of physically realizable atmospheric stabilities. We show that turbine-scale variables (e.g., hub height wind speed, standard deviation of the longitudinal wind speed, wind speed shear, wind directional shear and Richardson number) are strongly interrelated. Thus, we strongly advocate that these variables should not be prescribed as independent degrees of freedom in any synthetic turbulent inflow generator but rather that any Turbulence generation procedure should be able to bring about realistic sets of such physically realizable sets of turbine-scale flow variables. We demonstrate the utility of our LES-generated database in estimation of loads on a 5-MW wind turbine model. More importantly, we identify specific turbine-scale flow variables that are responsible for large turbine loads—e.g., wind speed shear is found to have a greater influence on out-of-plane blade bending moments for the turbine studied compared with its influence on other loads such as the tower-top yaw moment and the fore-aft tower base moment. Overall, our study suggests that LES may be effectively used to model inflow fields, to study characteristics of flow fields under various atmospheric stability conditions and to assess turbine loads for conditions that are not typically examined in design standards. Copyright © 2013 John Wiley & Sons, Ltd.
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large eddy simulation of stably stratified atmospheric Boundary Layer Turbulence a scale dependent dynamic modeling approach
Journal of the Atmospheric Sciences, 2006Co-Authors: Sukanta Basu, Fernando PorteagelAbstract:Abstract A new tuning-free subgrid-scale model, termed locally averaged scale-dependent dynamic (LASDD) model, is developed and implemented in large-eddy simulations (LES) of stable Boundary Layers. The new model dynamically computes the Smagorinsky coefficient and the subgrid-scale Prandtl number based on the local dynamics of the resolved velocity and temperature fields. Overall, the agreement between the statistics of the LES-generated Turbulence and some well-established empirical formulations and theoretical predictions (e.g., the local scaling hypothesis) is remarkable. Moreover, the simulated statistics obtained with the LASDD model show relatively little resolution dependence for the range of grid sizes considered here. In essence, it is shown here that the new LASDD model is a robust subgrid-scale parameterization for reliable, tuning-free simulations of stable Boundary Layers, even with relatively coarse resolutions.
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Revisiting the Local Scaling Hypothesis in Stably Stratified Atmospheric Boundary-Layer Turbulence: an Integration of Field and Laboratory Measurements with Large-Eddy Simulations
Boundary-Layer Meteorology, 2006Co-Authors: Sukanta Basu, Jean-françois Vinuesa, Fernando Porté-agel, Efi Foufoula-georgiou, Markus PahlowAbstract:The ‘local scaling’ hypothesis, first introduced by Nieuwstadt two decades ago, describes the Turbulence structure of the stable Boundary Layer in a very succinct way and is an integral part of numerous local closure-based numerical weather prediction models. However, the validity of this hypothesis under very stable conditions is a subject of ongoing debate. Here, we attempt to address this controversial issue by performing extensive analyses of Turbulence data from several field campaigns, wind-tunnel experiments and large-eddy simulations. A wide range of stabilities, diverse field conditions and a comprehensive set of Turbulence statistics make this study distinct
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revisiting the local scaling hypothesis in stably stratified atmospheric Boundary Layer Turbulence an integration of field and laboratory measurements with large eddy simulations
arXiv: Atmospheric and Oceanic Physics, 2005Co-Authors: Sukanta Basu, Jean-françois Vinuesa, Fernando Porteagel, Efi Foufoulageorgiou, Markus PahlowAbstract:The `local scaling' hypothesis, first introduced by Nieuwstadt two decades ago, describes the Turbulence structure of stable Boundary Layers in a very succinct way and is an integral part of numerous local closure-based numerical weather prediction models. However, the validity of this hypothesis under very stable conditions is a subject of on-going debate. In this work, we attempt to address this controversial issue by performing extensive analyses of Turbulence data from several field campaigns, wind-tunnel experiments and large-eddy simulations. Wide range of stabilities, diverse field conditions and a comprehensive set of Turbulence statistics make this study distinct.
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large eddy simulation of stably stratified atmospheric Boundary Layer Turbulence a scale dependent dynamic modeling approach
arXiv: Atmospheric and Oceanic Physics, 2005Co-Authors: Sukanta Basu, Fernando PorteagelAbstract:A new tuning-free subgrid-scale model, termed `locally-averaged scale-dependent dynamic' (LASDD) model, is developed and implemented in large-eddy simulations (LESs) of stable Boundary Layers. The new model dynamically computes the Smagorinsky coefficient and the subgrid-scale Prandtl number based on the local dynamics of the resolved velocity and temperature fields. Overall, the agreement between the statistics of the LES-generated Turbulence and some well-established empirical formulations and theoretical predictions (e.g., Nieuwstadt's local scaling hypothesis) is remarkable. The results show clear improvements over most of the traditional subgrid-scale models in the surface Layer. Moreover, in contrast to previous large-eddy simulations of stable Boundary Layers that have strong dependence on grid resolution, the simulated statistics obtained with the LASDD model show relatively little resolution dependence for the range of grid sizes considered here. In essence, we show that the new LASDD model is a robust subgrid-scale parameterization for reliable, tuning-free simulations of stable Boundary Layers, even with relatively coarse resolutions.
Alfred Wuest - One of the best experts on this subject based on the ideXlab platform.
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breathing sediments the control of diffusive transport across the sediment water interface by periodic Boundary Layer Turbulence
Limnology and Oceanography, 2003Co-Authors: Andreas Lorke, Beat Muller, Martin Maerki, Alfred WuestAbstract:We performed combined in situ measurements of bottom Boundary-Layer Turbulence and of diffusive oxygen fluxes at the sediment-water interface in a medium-sized mesotrophic lake. The Turbulence was driven by internal seiching with a period of 18 h. This periodic forcing, a prominent feature of enclosed water bodies, led to distinct deviations of the structure and the dynamics of the bottom Boundary Layer from the classical law-of-the-wall theory. A major feature was a phase lag between the current velocity and the turbulent energy dissipation of approximately 10% of the seiching period (1.5-2 h). The oxygen flux into the sediment was controlled by the diffusive Boundary Layer, the thickness of which varied between 0.16 and 0.84 mm during the course of a seiching period, and was strongly affected by the periodic bottom Boundary-Layer Turbulence. The rate of dissipation of turbulent energy in the bottom Boundary Layer allowed us to define the Batchelor length for dissolved oxygen, which quantifies the smallest scales of oxygen fluctuations and provides an appropriate scaling for the diffusive Boundary-Layer thickness and the corresponding oxygen fluxes. An analysis of the governing time scales revealed the importance of Turbulence in controlling the small-scale spatial heterogeneity of the diffusive fluxes. Higher Turbulence causes the diffusive Boundary Layer (DBL) to follow the sediment topography more smoothly, resulting in an increased area-averaged flux due to the greater effective surface area.
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breathing sediments the control of diffusive transport across the sediment water interface by periodic Boundary Layer Turbulence
Limnology and Oceanography, 2003Co-Authors: Andreas Lorke, Beat Muller, Martin Maerki, Alfred WuestAbstract:We performed combined in situ measurements of bottom Boundary-Layer Turbulence and of diffusive oxygen fluxes at the sediment‐water interface in a medium-sized mesotrophic lake. The Turbulence was driven by internal seiching with a period of 18 h. This periodic forcing, a prominent feature of enclosed water bodies, led to distinct deviations of the structure and the dynamics of the bottom Boundary Layer from the classical law-of-the-wall theory. A major feature was a phase lag between the current velocity and the turbulent energy dissipation of approximately 10% of the seiching period (1.5‐2 h). The oxygen flux into the sediment was controlled by the diffusive Boundary Layer, the thickness of which varied between 0.16 and 0.84 mm during the course of a seiching period, and was strongly affected by the periodic bottom Boundary-Layer Turbulence. The rate of dissipation of turbulent energy in the bottom Boundary Layer allowed us to define the Batchelor length for dissolved oxygen, which quantifies the smallest scales of oxygen fluctuations and provides an appropriate scaling for the diffusive Boundary-Layer thickness and the corresponding oxygen fluxes. An analysis of the governing time scales revealed the importance of Turbulence in controlling the small-scale spatial heterogeneity of the diffusive fluxes. Higher Turbulence causes the diffusive Boundary Layer (DBL) to follow the sediment topography more smoothly, resulting in an increased area-averaged flux due to the greater effective surface area. After surface zones, the bottom Boundary Layer (BBL) is the second prime site for animals, plants, and microorganisms in natural waters. From a physical and geochemical point of view, the importance of the BBL is twofold. First, the BBL is a major energy sink for basin-scale currents due to bottom friction and also due to the breaking of propagating internal waves on sloping bottoms (Imberger 1998). Consequently, the level of Turbulence is enhanced in the BBL compared with the interior water body. Second, the BBL controls the exchange of solutes and particles between water and sediment. The sediment surface is usually an enormous sink of oxygen due to the processes caused by the decomposition of organic matter. Furthermore, the redissolution and subsequent vertical transport of ions and other solutes supply primary producers with nutrients and affect the stability of the water column by chemical (salinity) strat
Peter P. Sullivan - One of the best experts on this subject based on the ideXlab platform.
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Boundary Layer Turbulence over surface waves in a strongly forced condition les and observation
Journal of Physical Oceanography, 2019Co-Authors: Nyla Husain, Tetsu Hara, Marc Buckley, Kianoosh Yousefi, Fabrice Veron, Peter P. SullivanAbstract:AbstractThe impact of sea state on air–sea momentum flux (or wind stress) is a poorly understood component of wind–wave interactions, particularly in high wind conditions. The wind stress and mean ...
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effect of planetary rotation on oceanic surface Boundary Layer Turbulence
Journal of Physical Oceanography, 2018Co-Authors: Junhong Liang, Peter P. Sullivan, James C. Mcwilliams, Qin ChenAbstract:AbstractA large-eddy simulation (LES) model is configured to investigate the effect of the horizontal (northward) component of Earth’s rotation on upper-ocean Turbulence. The focus is on the variab...
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frontogenesis and frontal arrest of a dense filament in the oceanic surface Boundary Layer
Journal of Fluid Mechanics, 2018Co-Authors: Peter P. Sullivan, James C. McwilliamsAbstract:The evolution of upper ocean currents involves a set of complex, poorly understood interactions between submesoscale Turbulence (e.g. density fronts and filaments and coherent vortices) and smaller-scale Boundary-Layer Turbulence. Here we simulate the lifecycle of a cold (dense) filament undergoing frontogenesis in the presence of Turbulence generated by surface stress and/or buoyancy loss. This phenomenon is examined in large-eddy simulations with resolved turbulent motions in large horizontal domains using grid points. Steady winds are oriented in directions perpendicular or parallel to the filament axis. Due to turbulent vertical momentum mixing, cold filaments generate a potent two-celled secondary circulation in the cross-filament plane that is frontogenetic, sharpens the cross-filament buoyancy and horizontal velocity gradients and blocks Ekman buoyancy flux across the cold filament core towards the warm filament edge. Within less than a day, the frontogenesis is arrested at a small width, , primarily by an enhancement of the Turbulence through a small submesoscale, horizontal shear instability of the sharpened filament, followed by a subsequent slow decay of the filament by further turbulent mixing. The Boundary-Layer Turbulence is inhomogeneous and non-stationary in relation to the evolving submesoscale currents and density stratification. The occurrence of frontogenesis and arrest are qualitatively similar with varying stress direction or with convective cooling, but the detailed evolution and flow structure differ among the cases. Thus submesoscale filament frontogenesis caused by Boundary-Layer Turbulence, frontal arrest by frontal instability and frontal decay by forward energy cascade, and turbulent mixing are generic processes in the upper ocean.
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frontogenesis and frontal arrest of a dense filament in the oceanic surface Boundary Layer
Journal of Fluid Mechanics, 2018Co-Authors: Peter P. Sullivan, James C. McwilliamsAbstract:The evolution of upper ocean currents involves a set of complex, poorly understood interactions between submesoscale Turbulence (e.g. density fronts and filaments and coherent vortices) and smaller-scale Boundary-Layer Turbulence. Here we simulate the lifecycle of a cold (dense) filament undergoing frontogenesis in the presence of Turbulence generated by surface stress and/or buoyancy loss. This phenomenon is examined in large-eddy simulations with resolved turbulent motions in large horizontal domains using ${\sim}10^{10}$ grid points. Steady winds are oriented in directions perpendicular or parallel to the filament axis. Due to turbulent vertical momentum mixing, cold filaments generate a potent two-celled secondary circulation in the cross-filament plane that is frontogenetic, sharpens the cross-filament buoyancy and horizontal velocity gradients and blocks Ekman buoyancy flux across the cold filament core towards the warm filament edge. Within less than a day, the frontogenesis is arrested at a small width, ${\approx}100~\text{m}$ , primarily by an enhancement of the Turbulence through a small submesoscale, horizontal shear instability of the sharpened filament, followed by a subsequent slow decay of the filament by further turbulent mixing. The Boundary-Layer Turbulence is inhomogeneous and non-stationary in relation to the evolving submesoscale currents and density stratification. The occurrence of frontogenesis and arrest are qualitatively similar with varying stress direction or with convective cooling, but the detailed evolution and flow structure differ among the cases. Thus submesoscale filament frontogenesis caused by Boundary-Layer Turbulence, frontal arrest by frontal instability and frontal decay by forward energy cascade, and turbulent mixing are generic processes in the upper ocean.
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wave Boundary Layer Turbulence over surface waves in a strongly forced condition
Journal of Physical Oceanography, 2015Co-Authors: Tetsu Hara, Peter P. SullivanAbstract:AbstractAccurate predictions of the sea state–dependent air–sea momentum flux require a thorough understanding of the wave Boundary Layer Turbulence over surface waves. A set of momentum and energy equations is derived to formulate and analyze wave Boundary Layer Turbulence. The equations are written in wave-following coordinates, and all variables are decomposed into horizontal mean, wave fluctuation, and turbulent fluctuation. The formulation defines the wave-induced stress as a sum of the wave fluctuation stress (because of the fluctuating velocity components) and a pressure stress (pressure acting on a tilted surface). The formulations can be constructed with different choices of mapping. Next, a large-eddy simulation result for wind over a sinusoidal wave train under a strongly forced condition is analyzed using the proposed formulation. The result clarifies how surface waves increase the effective roughness length and the drag coefficient. Specifically, the enhanced wave-induced stress close to the ...
Christophe S Etherto - One of the best experts on this subject based on the ideXlab platform.
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a new parameterization for shallow cumulus convection and its application to marine subtropical cloud topped Boundary Layers part ii regional simulations of marine Boundary Layer clouds
Monthly Weather Review, 2004Co-Authors: James R Mccaa, Christophe S EthertoAbstract:Abstract The impact of physical parameterizations on simulations of cloud-topped marine Boundary Layers is investigated using the fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5). Three-month MM5 simulations of the northeast and southeast Pacific during June–August 1987 are Boundary forced with time- varying ECMWF analyses. Runs with four planetary Boundary Layer (PBL) parameterizations already implemented in MM5 are compared with runs using new parameterizations of Boundary Layer Turbulence and shallow cumulus convection (ShCu) described in a companion paper. Numerous modifications to the MM5 that allow it to be used as a regional climate model are described. The simulated 3-month mean shortwave cloud radiative forcing (SWCF) and vertical structure of cloud-topped Boundary Layers in the northeast Pacific are sensitive to the PBL/shallow convection schemes. All four current MM5 PBL schemes [the Blackadar, Medium-Range Forecast (MRF), Burk–Thompson, and Gayno–Seaman schemes] produc...