Experimental study of the horizontally averaged flow structure in a model wind-turbine array boundary layer

Cal, Raúl Bayoán; Lebron, Jose; Castillo, Luciano; Kang, Hyung Suk; Meneveau, Charles

doi:10.1063/1.3289735

Cited by 288 publications

(271 citation statements)

References 34 publications

Supporting

Mentioning

250

Contrasting

Unclassified

Order By: Relevance

“…5e). This contrast between TI andē values suggests that vertical velocity variations contribute most to the turbulence enhancement above the turbine rotor layer during the evening transition, consistent with previous wind-tunnel studies (Cal et al 2010) and idealized LES results (Calaf et al 2010), which emphasize the importance of the vertical flux stimulated by wakes.…”

Section: Wind Speed Deficits and Turbulence Generationsupporting

confidence: 77%

Observing and Simulating Wind-Turbine Wakes During the Evening Transition

Lee

Lundquist

2017

Boundary-Layer Meteorol

View full text Add to dashboard Cite

Wind-turbine-wake evolution during the evening transition introduces variability to wind-farm power production at a time of day typically characterized by high electricity demand. During the evening transition, the atmosphere evolves from an unstable to a stable regime, and vertical stratification of the wind profile develops as the residual planetary boundary layer decouples from the surface layer. The evolution of wind-turbine wakes during the evening transition is examined from two perspectives: wake observations from single turbines, and simulations of multiple turbine wakes using the mesoscale Weather Research and Forecasting (WRF) model. Throughout the evening transition, the wake's wind-speed deficit and turbulence enhancement are confined within the rotor layer when the atmospheric stability changes from unstable to stable. The height variations of maximum upwind-downwind differences of wind speed and turbulence intensity gradually decrease during the evening transition. After verifying the WRF-model-simulated upwind wind speed, wind direction and turbulent kinetic energy profiles with observations, the wind-farm-scale wake evolution during the evening transition is investigated using the WRF-model wind-farm parametrization scheme. As the evening progresses, due to the presence of the wind farm, the modelled hub-height wind-speed deficit monotonically increases, the relative turbulence enhancement at hub height grows by 50%, and the downwind surface sensible heat flux increases, reducing surface cooling. Overall, the intensifying wakes from upwind turbines respond to the evolving atmospheric boundary layer during the evening transition, and undermine the power production of downwind turbines in the evening.

show abstract

Section: Wind Speed Deficits and Turbulence Generationsupporting

confidence: 77%

Observing and Simulating Wind-Turbine Wakes During the Evening Transition

Lee

Lundquist

2017

Boundary-Layer Meteorol

View full text Add to dashboard Cite

show abstract

“…As expected from other wind tunnel studies for wind energy [36][37][38], positive values of −uv occur above hub height in the wake. This component of the Reynolds shear stresses is associated with the vertical flux of mean flow kinetic energy by turbulence and remediation of the wake.…”

Section: A Turbulence Fieldsupporting

confidence: 55%

Anisotropic character of low-order turbulent flow descriptions through the proper orthogonal decomposition

2017

Self Cite

View full text Add to dashboard Cite

Proper orthogonal decomposition (POD) is applied to distinct data sets in order to characterize the propagation of error arising from basis truncation in the description of turbulence. Experimental data from stereo particle image velocimetry measurements in a wind turbine array and direct numerical simulation data from a fully developed channel flow are used to illustrate dependence of the anisotropy tensor invariants as a function of POD modes used in low-order descriptions. In all cases, ensembles of snapshots illuminate a variety of anisotropic states of turbulence. In the near wake of a model wind turbine, the turbulence field reflects the periodic interaction between the incoming flow and rotor blade. The far wake of the wind turbine is more homogenous, confirmed by the increased magnitude of the anisotropy factor. By contrast, the channel flow exhibits many anisotropic states of turbulence. In the inner layer of the wall-bounded region, one observes onecomponent turbulence at the wall; immediately above, the turbulence is dominated by two components, with the outer layer showing fully three-dimensional turbulence, conforming to theory for wall-bounded turbulence. The complexity of flow descriptions resulting from truncated POD bases can be greatly mitigated by severe basis truncations. However, the current work demonstrates that such simplification necessarily exaggerates the anisotropy of the modeled flow and, in extreme cases, can lead to the loss of three-dimensionality. Application of simple corrections to the low-order descriptions of the Reynolds stress tensor significantly reduces the residual root-mean-square error. Similar error reduction is seen in the anisotropy tensor invariants. Corrections of this form reintroduce three-dimensionality to severe truncations of POD bases. A threshold for truncating the POD basis based on the equivalent anisotropy factor for each measurement set required many more modes than a threshold based on energy. The mode requirement to reach the anisotropy threshold after correction is reduced by a full order of magnitude for all example data sets, ensuring that economical low-dimensional models account for the isotropic quality of the turbulence field.

show abstract

“…Although the turbulence intensity could intuitively be associated with the flow mixing, it has been demonstrated that the Reynolds shear stresses uv, uw, and vw are responsible of the flow kinetic energy transport (Antonia et al, 1986;Cal et al, 2010;Cantwell and Coles, 1983;Escudie and Line, 2003;Hussain, 1983;and Reynolds and Hussain, 1972) and that as such they must be taken into consideration for evaluating the turbulent mixing in a particular region of the flow. For this reason, the last term of Equation (2), which represents the spatial gradients of the flux of mean-flow kinetic energy, has been evaluated in the x-y plane as U ¼ Àuðu 0 v 0 Þ (streamwise mean-flow kinetic energy flux in the radial direction).…”

Section: F Wake Mixingmentioning

confidence: 99%

Experimental comparison of a wind-turbine and of an actuator-disc near wake

Lignarolo

Ragni

Ferreira

et al. 2016

Journal of Renewable and Sustainable Energy

View full text Add to dashboard Cite

The actuator disc (AD) model is commonly used to simplify the simulation of horizontal-axis wind-turbine aerodynamics. The limitations of this approach in reproducing the wake losses in wind farm simulations have been proven by a previous research. The present study is aimed at providing an experimental analysis of the near-wake turbulent flow of a wind turbine (WT) and a porous disc, emulating the actuator disc numerical model. The general purpose is to highlight the similarities and to quantify the differences of the two models in the near-wake region, characterised by the largest discrepancies. The velocity fields in the wake of a wind turbine model and a porous disc (emulation of the actuator disc numerical model) have been measured in a wind tunnel using stereo particle image velocimetry. The study has been conducted at low turbulence intensity in order to separate the problems of the flow mixing caused by the external turbulence and the one caused by the turbulence induced directly by the AD or the WT presence. The analysis, as such, showed the intrinsic differences and similarities between the flows in the two wakes, solely due to the wake-induced flow, with no influence of external flow fluctuations. The data analysis provided the time-average three-component velocity and turbulence intensity fields, pressure fields, rotor and disc loading, vorticity fields, stagnation enthalpy distribution, and mean-flow kinetic-energy fluxes in the shear layer at the border of the wake. The properties have been compared in the wakes of the two models. Even in the absence of turbulence, the results show a good match in the thrust and energy coefficient, velocity, pressure, and enthalpy fields between wind turbine and actuator disc. However, the results show a different turbulence intensity and turbulent mixing. The results suggest the possibility to extend the use of the actuator disc model in numerical simulation until the very near wake, provided that the turbulent mixing is correctly represented.

show abstract

Experimental study of the horizontally averaged flow structure in a model wind-turbine array boundary layer

Cited by 288 publications

References 34 publications

Observing and Simulating Wind-Turbine Wakes During the Evening Transition

Observing and Simulating Wind-Turbine Wakes During the Evening Transition

Anisotropic character of low-order turbulent flow descriptions through the proper orthogonal decomposition

Experimental comparison of a wind-turbine and of an actuator-disc near wake

Contact Info

Product

Resources

About