The superposition of a rotating wake with the atmospheric Ekman spiral 

2021 ◽  
Author(s):  
Antonia Englberger ◽  
Andreas Dörnbrack ◽  
Julie K. Lundquist
Keyword(s):  
Wind Turbine ◽  
Streamwise Velocity ◽  
Atmospheric Boundary Layers ◽  
Flow Component ◽  
Large Eddy ◽  
Basic Physics ◽  
Northern Hemispheric ◽  
The Relationship ◽  
Spanwise Flow ◽  
Rotational Direction

<p align="justify"><span>Stably stratified atmospheric boundary layers are often characterized by a veering wind profile, in which the wind direction changes clockwise (counterclockwise) with height in the Northern Hemisphere (Southern Hemisphere). Wind-turbine wakes respond to this veer in the incoming wind by stretching from a circular shape into an ellipsoid. Englberger, Dörnbrack and Lundquist (2020) investigate the relationship between this stretching and the direction of the turbine rotation by means of large-eddy simulations </span><span>(LESs)</span>.</p><p align="justify"><span>The basic physics underlying the interaction process of a rotating </span><span>wake</span><span> with a veering inflow can be described with the superposition of a Rankine vortex as representation of the wind-turbine </span><span>wake</span><span> with the characteristic </span><span>hemispheric-dependent </span><span>nighttime Ekman spiral of the atmospheric wind. </span><span>In dependence of the rotational direction </span><span>an</span><span>d</span><span> the hemisphere, this</span><span> superposition results in an amplification of the spanwise flow component if a </span><span>counterclockwise</span><span> rotating </span><span>rotor interacts with a northern hemispheric Ekman spiral </span><span>(</span><span>a clockwise rotating rotor interacts with a southern hemispheric Ekman spiral</span><span>)</span><span>. In case of a clockwise rotating rotor interacting with a northern hemispheric Ekman spiral </span><span>(</span><span>a counterclockwise rotating </span> <span>rotor interacting with a southern hemispheric Ekman spiral</span><span>)</span><span>, the superposition leads to a weakening of the spanwise flow component. In case of no veering inflow, the magnitude of the spanwise flow component is independent of the rotational direction.</span></p><p align="justify"><span>Th</span><span>ese theoretical</span> <span>superposition </span><span>effect</span><span> of the Ekman layer with the wake vortex </span><span>occur in nighttime </span><span>LESs, </span><span>where t</span><span>he rotational direction dependent magintude of the spanwise flow component further impacts the streamwise flow component in the wake. In particular, </span><span>there is a rotational direction dependent difference in </span><span>the </span><span>wake strength, </span><span>the </span><span>extension </span><span>of the wake</span><span>, </span><span>the wake </span><span>width, and </span><span>the wake </span><span>deflection </span><span>angle. </span><span>In more detail, a </span><span>northern hemispheric </span><span>veering wind in combination with a counterclockwise rotating actuator results in a larger streamwise velocity output, a larger spanwise wake width, and a larger wake deflection angle at the same downwind distance in comparison to a clockwise rotating turbine.</span></p><p><span>Englberger, Dörnbrack and Lundquist, 2020, Does the rotational direction of a wind turbine impact the wake in a stably stratified atmospheric boundary layer? </span><span><em>Wind Energ. Sci. </em></span><span><strong>5</strong></span><span>, 1359-1374.</span></p>

scholarly journals On Wind Turbine Loads During Thunderstorm Downbursts in Contrasting Atmospheric Stability Regimes

Energies ◽  
2019 ◽  
Vol 12 (14) ◽  
pp. 2773 ◽  
Author(s):  
Nan-You Lu ◽  
Patrick Hawbecker ◽  
Sukanta Basu ◽  
Lance Manuel
Keyword(s):  
Wind Turbine ◽  
Structural Integrity ◽  
Atmospheric Stability ◽  
International Electrotechnical Commission ◽  
Large Eddy Simulation Model ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Turbine Design ◽  
The Relationship ◽  
Inflow Conditions

Severe winds produced by thunderstorm downbursts pose a serious risk to the structural integrity of wind turbines. However, guidelines for wind turbine design (such as the International Electrotechnical Commission Standard, IEC 61400-1) do not describe the key physical characteristics of such events realistically. In this study, a large-eddy simulation model is employed to generate several idealized downburst events during contrasting atmospheric stability conditions that range from convective through neutral to stable. Wind and turbulence fields generated from this dataset are then used as inflow for a 5-MW land-based wind turbine model; associated turbine loads are estimated and compared for the different inflow conditions. We first discuss time-varying characteristics of the turbine-scale flow fields during the downbursts; next, we investigate the relationship between the velocity time series and turbine loads as well as the influence and effectiveness of turbine control systems (for blade pitch and nacelle yaw). Finally, a statistical analysis is conducted to assess the distinct influences of the contrasting stability regimes on extreme and fatigue loads on the wind turbine.

scholarly journals Changing the rotational direction of a wind turbine under veering inflow: a parameter study

2020 ◽  
Vol 5 (4) ◽  
pp. 1623-1644
Author(s):  
Antonia Englberger ◽  
Julie K. Lundquist ◽  
Andreas Dörnbrack
Keyword(s):  
Wind Speed ◽  
Wind Turbine ◽  
Northern Hemisphere ◽  
Deflection Angle ◽  
Turbine Blades ◽  
Streamwise Velocity ◽  
Rotational Frequency ◽  
Parameter Study ◽  
Wind Component ◽  
Rotational Direction

Abstract. All current-day wind-turbine blades rotate in clockwise direction as seen from an upstream perspective. The choice of the rotational direction impacts the wake if the wind profile changes direction with height. Here, we investigate the respective wakes for veering and backing winds in both hemispheres by means of large-eddy simulations. We quantify the sensitivity of the wake to the strength of the wind veer, the wind speed, and the rotational frequency of the rotor in the Northern Hemisphere. A veering wind in combination with counterclockwise-rotating blades results in a larger streamwise velocity output, a larger spanwise wake width, and a larger wake deflection angle at the same downwind distance in comparison to a clockwise-rotating turbine in the Northern Hemisphere. In the Southern Hemisphere, the same wake characteristics occur if the turbine rotates counterclockwise. These downwind differences in the wake result from the amplification or weakening or reversion of the spanwise wind component due to the effect of the superimposed vortex of the rotor rotation on the inflow's shear. An increase in the directional shear or the rotational frequency of the rotor under veering wind conditions increases the difference in the spanwise wake width and the wake deflection angle between clockwise- and counterclockwise-rotating actuators, whereas the wind speed lacks a significant impact.

Performance of a Cross-Flow Wind Turbine Located Above a Windbreak Fence

2015 ◽  
Author(s):  
Haruka Sakai ◽  
Takahiro Kiwata ◽  
Hiroaki Nakata ◽  
Takaaki Kono ◽  
Hiroko Furumichi ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Flow Analysis ◽  
Cross Flow ◽  
Velocity Fields ◽  
Power Coefficient ◽  
Two Dimensional ◽  
Ansys Fluent ◽  
The Relationship ◽  
Rotational Direction ◽  
Porous Fence

The performance of a cross-flow wind turbine located above a windbreak fence (snowbreak fence) and the associated velocity fields were investigated through wind tunnel tests. The effects of the amount of vertical clearance between the wind turbine and the fence, the percentage of the fence area that is nonporous, and the rotational direction of the turbine were examined. In addition, a two-dimensional numerical flow analysis of the cross-flow wind turbine above the fence was performed using the CFD software ANSYS FLUENT 13.0. The fence and wind turbine models were built to a scale of 1:5; the porous fence model had a height of h = 500 mm, and the diameter of the wind turbine was 80 mm. It was found that the relationship between the inflow velocity into the clearance gap and the rotational direction of the turbine affects the power coefficient of the turbine.

Calculating the aerodynamics of vertical axis wind turbines

2012 ◽  
Vol 34 (3) ◽  
pp. 169-184 ◽  
Author(s):  
Hoang Thi Bich Ngoc
Keyword(s):  
Wind Turbine ◽  
Incidence Angle ◽  
Vertical Axis ◽  
Rotor Blades ◽  
Vertical Axis Wind Turbine ◽  
Horizontal Axis Wind Turbine ◽  
Velocity Triangle ◽  
Relationship Of ◽  
The Relationship

Vertical axis wind turbine technology has been applied last years, very long after horizontal axis wind turbine technology. Aerodynamic problems of vertical axis wind machines are discussible. An important problem is the determination of the incidence law in the interaction between wind and rotor blades. The focus of the work is to establish equations of the incidence depending on the blade azimuth, and to solve them. From these results, aerodynamic torques and power can be calculated. The incidence angle is a parameter of velocity triangle, and both the factors depend not only on the blade azimuth but also on the ratio of rotational speed and horizontal speed. The built computational program allows theoretically selecting the relationship of geometric parameters of wind turbine in accordance with requirements on power, wind speed and installation conditions.

Abilities of Physics Education Students in Constructing Graphics Based on Practicum Results and in Interpreting It

2020 ◽  
Vol 3 (1) ◽  
pp. 35-44
Author(s):  
Hariawan Hariawan ◽  
Muslimin Muslimin ◽  
I Komang Werdhiana
Keyword(s):  
Physics Education ◽  
Research Subjects ◽  
Education Students ◽  
Study Program ◽  
Thinking Aloud ◽  
Training And Education ◽  
Education Study ◽  
Basic Physics ◽  
Undergraduate Physics Education ◽  
The Relationship

The skills to construct and interpret graphs are a form of science skills and are an important component in learning physics. The purpose of this study was to describe the ability of undergraduate physics education students to construct graphs based on practicum data and interpret them. Data obtained through respondent answer sheets, thinking-aloud recordings, and interviews. The research was conducted at the Faculty of Teacher Training and Education (FKIP) Untad and the research subjects of the Physics Education Study Program students were 6 people obtained based on the values of Basic Physics I and Basic Physics practicum II then divided into three groups of levels (high, medium, and low) with each category as many as 2 people. The results of this study indicate: 1) in general, respondents in the high, medium, and low categories can construct graphs but are not based on the prerequisite ability to construct graphs, especially in determining the x-axis and y-axis variables, 2) on the ability to interpret graphs, respondents can interpret graphs the relationship between variables on the graph but not supported by an explanation or evaluation based on proper physics concepts, 3) The strategy used by respondents in constructing graphs, in general, is to convert data in decimal form or scientific notation and 4) The difficulties experienced by respondents when constructing graphs are converting data, determining the scale and how to determine the variables on each graph axis.    

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.

Recent improvements of actuator line-large-eddy simulation method for wind turbine wakes

2021 ◽  
Vol 42 (4) ◽  
pp. 511-526
Author(s):  
Zhiteng Gao ◽  
Ye Li ◽  
Tongguang Wang ◽  
Shitang Ke ◽  
Deshun Li
Keyword(s):  
Large Eddy Simulation ◽  
Wind Turbine ◽  
Simulation Method ◽  
Eddy Simulation ◽  
Large Eddy

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

A control-oriented large eddy simulation of wind turbine wake considering effects of Coriolis force and time-varying wind conditions

Energy ◽  
2022 ◽  
Vol 239 ◽  
pp. 121876
Author(s):  
Guo-Wei Qian ◽  
Yun-Peng Song ◽  
Takeshi Ishihara
Keyword(s):  
Large Eddy Simulation ◽  
Wind Turbine ◽  
Coriolis Force ◽  
Time Varying ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Turbine Wake ◽  
Wind Turbine Wake
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