scholarly journals Investigating wind turbine impacts on near-wake flow using profiling lidar data and large-eddy simulations with an actuator disk model

2015 ◽  
Vol 7 (4) ◽  
pp. 043143 ◽  
Author(s):  
Jeffrey D. Mirocha ◽  
Daniel A. Rajewski ◽  
Nikola Marjanovic ◽  
Julie K. Lundquist ◽  
Branko Kosović ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Large Eddy Simulations ◽  
Wake Flow ◽  
Lidar Data ◽  
Near Wake ◽  
Disk Model ◽  
Actuator Disk ◽  
Large Eddy

scholarly journals Large-Eddy Simulation of Yawed Wind-Turbine Wakes: Comparisons with Wind Tunnel Measurements and Analytical Wake Models

Energies ◽  
2019 ◽  
Vol 12 (23) ◽  
pp. 4574 ◽  
Author(s):  
Mou Lin ◽  
Fernando Porté-Agel
Keyword(s):  
Wind Tunnel ◽  
Large Eddy Simulation ◽  
Wind Turbine ◽  
Wind Farms ◽  
Disk Model ◽  
Actuator Disk ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Wind Tunnel Measurements ◽  
Tangential Forces

In this study, we validated a wind-turbine parameterisation for large-eddy simulation (LES) of yawed wind-turbine wakes. The presented parameterisation is modified from the rotational actuator disk model (ADMR), which takes account of both thrust and tangential forces induced by a wind turbine based on the blade-element theory. LES results using the yawed ADMR were validated with wind-tunnel measurements of the wakes behind a stand-alone miniature wind turbine model with different yaw angles. Comparisons were also made with the predictions of analytical wake models. In general, LES results using the yawed ADMR are in good agreement with both wind-tunnel measurements and analytical wake models regarding wake deflections and spanwise profiles of the mean velocity deficit and the turbulence intensity. Moreover, the power output of the yawed wind turbine is directly computed from the tangential forces resolved by the yawed ADMR, in contrast with the indirect power estimation used in the standard actuator disk model. We found significant improvement in the power prediction from LES using the yawed ADMR over the simulations using the standard actuator disk without rotation, suggesting a good potential of the yawed ADMR to be applied in LES studies of active yaw control in wind farms.

scholarly journals How does turbulence change approaching a rotor?

2017 ◽  
Author(s):  
Jakob Mann ◽  
Alfredo Peña ◽  
Niels Troldborg ◽  
Søren J. Andersen
Keyword(s):  
Wind Speed ◽  
Wind Turbines ◽  
Low Frequency ◽  
Large Eddy Simulations ◽  
Thrust Coefficient ◽  
Disk Model ◽  
Actuator Disk ◽  
Large Eddy ◽  
Rotor Support ◽  
Induction Zone

Abstract. For load calculations on wind turbines it is usually assumed that the turbulence approaching the rotor does not change its statistics as it goes through the induction zone. We investigate this assumption using a nacelle-mounted forward-looking pulsed lidar that measures low frequency wind fluctuations simultaneous at distances between one half and three rotor diameters upstream. The measurements show that below rated wind speed the low-frequency wind variance is reduced by up to 10 % at one half rotor diameter upstream and above rated enhanced by up to 20 %. A quasi-steady model that takes into account the change of thrust coefficient with wind speed explains these variations partly. Large-eddy simulations of turbulence approaching an actuator disk model of a rotor support the finding that the slope of the thrust curve influences the low-frequency fluctuations.

Understanding the Influence of Turbine Geometry and Atmospheric Turbulence on Wind Turbine Wakes

2016 ◽  
Author(s):  
Ping Gu ◽  
Jim Y. J. Kuo ◽  
David A. Romero ◽  
Cristina H. Amon
Keyword(s):  
Wind Turbine ◽  
Atmospheric Turbulence ◽  
Aerodynamic Force ◽  
Atmospheric Condition ◽  
Atmospheric Effects ◽  
Wake Region ◽  
Near Wake ◽  
Disk Model ◽  
Actuator Disk ◽  
Far Wake

A wind turbine wake is divided into two regions, near wake and far wake. In the near wake region, the flow is highly turbulent and is strongly influenced by the rotor geometry. In the far wake region, the influence of rotor geometry becomes less important as atmospheric effects become dominant. However, how turbine geometry and atmospheric condition affect the two wake regions is not well studied. In this work, the influence of atmospheric turbulence and the blade aerodynamic forces on wake development is studied using computational fluid dynamics (CFD) models. The CFD simulation results are based on an actuator disk model and an k–ε turbulence model. The effects of blade geometry are captured by prescribing aerodynamics forces exerted by a LM8.2 blade on an actuator disk, and are compared with that of an equivalent uniform normalized force, under two atmospheric turbulence conditions. The finding shows that the length of the near wake region is strongly affected by atmospheric turbulence, with the wake becoming fully developed as far as 2.5 rotor diameters downstream of the rotor under low turbulence conditions. Furthermore, the velocity profile in the far wake region is independent of the blade profile. In other words, in the cases studied, an actuator disk with an equivalent uniform force will produce nearly identical velocity profiles in the far wake region as one with nonuniform aerodynamic force profiles. These findings have implications on existing wake models where the far wake is the region of interest. Specifically, the beginning of the far wake region should be properly defined for each scenario, and that it is not necessary to provide detailed rotor geometry for far wake simulations.

scholarly journals How does turbulence change approaching a rotor?

2018 ◽  
Vol 3 (1) ◽  
pp. 293-300 ◽  
Author(s):  
Jakob Mann ◽  
Alfredo Peña ◽  
Niels Troldborg ◽  
Søren J. Andersen
Keyword(s):  
Wind Speed ◽  
Wind Turbines ◽  
Low Frequency ◽  
Large Eddy Simulations ◽  
Thrust Coefficient ◽  
Disk Model ◽  
Actuator Disk ◽  
Large Eddy ◽  
Rotor Support ◽  
Induction Zone

Abstract. For load calculations on wind turbines it is usually assumed that the turbulence approaching the rotor does not change its statistics as it goes through the induction zone. We investigate this assumption using a nacelle-mounted forward-looking pulsed lidar that measures low-frequency wind fluctuations simultaneously at distances between 0.5 and 3 rotor diameters upstream. The measurements show that below rated wind speed the low-frequency wind variance is reduced by up to 10 % at 0.5 rotor diameters upstream and above rated enhanced by up to 20 %. A quasi-steady model that takes into account the change in thrust coefficient with wind speed explains these variations partly. Large eddy simulations of turbulence approaching an actuator disk model of a rotor support the finding that the slope of the thrust curve influences the low-frequency fluctuations.

scholarly journals Large-Eddy Simulation of Wind Turbine Flows: A New Evaluation of Actuator Disk Models

Energies ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3745
Author(s):  
Tristan Revaz ◽  
Fernando Porté-Agel
Keyword(s):  
Boundary Layer ◽  
Simple Model ◽  
Wind Turbine ◽  
Wake Flow ◽  
Test Case ◽  
Flow Solver ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Layer Flow ◽  
Advanced Model

Large-eddy simulation (LES) with actuator models has become the state-of-the-art numerical tool to study the complex interaction between the atmospheric boundary layer (ABL) and wind turbines. In this paper, a new evaluation of actuator disk models (ADMs) for LES of wind turbine flows is presented. Several details of the implementation of such models are evaluated based on a test case studied experimentally. In contrast to other test cases used in previous similar studies, the present test case consists of a wind turbine immersed in a realistic turbulent boundary-layer flow, for which accurate data for the turbine, the flow, the thrust and the power are available. It is found that the projection of the forces generated by the turbine into the flow solver grid is crucial for rotor predictions, especially for the power, and less important for the wake flow prediction. In this context, the projection of the forces into the flow solver grid should be as accurate as possible, in order to conserve the consistency between the computed axial velocity and the projected axial force. Also, the projection of the force is found to be much more important in the rotor plane directions than in the streamwise direction. It is found that for the case of a wind turbine immersed in a realistic turbulent boundary-layer flow, the potential spurious numerical oscillations originating from sharp force projections are not harmful to the results. By comparing an advanced model which computes the non-uniform distribution of the turbine forces over the rotor with a simple model which assumes uniform effects of the turbine forces, it is found that both can lead to accurate results for the far wake flow and the thrust and power predictions. However, the comparison shows that the advanced model leads to better results for the near wake flow. In addition, it is found that the simple model overestimates the rotor velocity prediction in comparison to the advanced model. These elements are explained by the lack of local feedback between the axial velocity and the axial force in the simple model. By comparing simulations with and without including the effects of the nacelle and tower, it is found that the consideration of the nacelle and tower is relatively important both for the near wake and the power prediction, due to the shadow effects. The grid resolution is not found to be critical once a reasonable resolution is used, i.e. in the order of 10 grid points along each direction across the rotor. The comparison with the experimental data shows that an accurate prediction of the flow, thrust, and power is possible with a very reasonable computational cost. Overall, the results give important guidelines for the implementation of ADMs for LES.

scholarly journals Wake meandering statistics of a model wind turbine: Insights gained by large eddy simulations

2016 ◽  
Vol 1 (4) ◽  
Author(s):  
Daniel Foti ◽  
Xiaolei Yang ◽  
Michele Guala ◽  
Fotis Sotiropoulos
Keyword(s):  
Wind Turbine ◽  
Large Eddy Simulations ◽  
Large Eddy

Near-Wake Flow Simulations for a Mid-Sized Rim Driven Wind Turbine

2013 ◽  
Author(s):  
Bryan Kaiser ◽  
Svetlana Poroseva ◽  
Erick L. Johnson ◽  
Rob Hovsapian
Keyword(s):  
Wind Turbine ◽  
Wake Flow ◽  
Near Wake ◽  
Flow Simulations

Experimental Investigation on the Tip Vortex of a Wind Turbine With and Without a Slotted Tip

2017 ◽  
Author(s):  
Pengyin Liu ◽  
Jinge Chen ◽  
Shen Xin ◽  
Xiaocheng Zhu ◽  
Zhaohui Du
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Wind Turbine ◽  
Vortex Core ◽  
Control Method ◽  
Tip Vortex ◽  
Wake Flow ◽  
Core Model ◽  
Near Wake ◽  
Measured Velocity

In this paper, a slotted tip structure is experimentally analyzed. A wind turbine with three blades, of which the radius is 301.74mm, is investigated by the PIV method. Each wind turbine blade is formed with a slots system comprising four internal tube members embedded in the blade. The inlets of the internal tube member are located at the leading edge of the blade and form an inlet array. The outlets are located at the blade tip face and form an outlet array. The near wake flow field of the wind turbine with slotted tip and without slotted tip are both measured. Velocity field of near wake region and clear images of the tip vortex are captured under different wake ages. The experimental results show that the radius of the tip vortex core is enlarged by the slotted tip at any wake age compared with that of original wind turbine. Moreover, the diffusion process of the tip vortex is accelerated by the slotted tip which lead to the disappearance of the tip vortex occurs at smaller wake age. The strength of the tip vortex is also reduced indicating that the flow field in the near wake of wind turbine is improved. The experimental data are further analyzed with the vortex core model to reveal the flow mechanism of this kind of flow control method. The turbulence coefficient of the vortex core model for wind turbine is obtained from the experimental data of the wind turbine with and without slotted tip. It shows that the slotted tip increases the turbulence strength in the tip vortex core by importing airflow into the tip vortex core during its initial generation stage, which leads to the reduction of the tip vortex strength. Therefore, it is promising that the slotted tip can be used to weaken the vorticity and accelerate the diffusion of the tip vortex which would improve the problem caused by the tip vortex.

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