scholarly journals A Simulation Study on Risks to Wind Turbine Arrays from Thunderstorm Downbursts in Different Atmospheric Stability Conditions

Energies ◽  
2021 ◽  
Vol 14 (17) ◽  
pp. 5407
Author(s):  
Nan-You Lu ◽  
Lance Manuel ◽  
Patrick Hawbecker ◽  
Sukanta Basu
Keyword(s):  
Boundary Layer ◽  
Wind Turbine ◽  
Transition Period ◽  
Atmospheric Stability ◽  
Bending Moment ◽  
Stability Conditions ◽  
Wind Fields ◽  
Worst Case ◽  
Large Eddy Simulation Model ◽  
Turbine Arrays

Thunderstorm downbursts have been reported to cause damage or failure to wind turbine arrays. We extend a large-eddy simulation model used in previous work to generate downburst-related inflow fields with a view toward defining correlated wind fields that all turbines in an array would experience together during a downburst. We are also interested in establishing what role contrasting atmospheric stability conditions can play on the structural demands on the turbines. This interest is because the evening transition period, when thunderstorms are most common, is also when there is generally acknowledged time-varying stability in the atmospheric boundary layer. Our results reveal that the structure of a downburst’s ring vortices and dissipation of its outflow play important roles in the separate inflow fields for turbines located at different parts of the array; these effects vary with stability. Interacting with the ambient winds, the outflow of a downburst is found to have greater impacts in an “average” sense on structural loads for turbines farther from the touchdown center in the stable cases. Worst-case analyses show that the largest extreme loads, although somewhat dependent on the specific structural load variable considered, depend on the location of the turbine and on the prevailing atmospheric stability. The results of our calculations show the highest simulated foreaft tower bending moment to be 85.4 MN-m, which occurs at a unit sited in the array farther from touchdown center of the downburst initiated in a stable boundary layer.

scholarly journals Numerical Analysis of the Effect of Offshore Turbulent Wind Inflow on the Response of a Spar Wind Turbine

Energies ◽  
2020 ◽  
Vol 13 (10) ◽  
pp. 2506
Author(s):  
Rieska Mawarni Putri ◽  
Charlotte Obhrai ◽  
Jasna Bogunovic Jakobsen ◽  
Muk Chen Ong
Keyword(s):  
Wind Turbine ◽  
Energy Content ◽  
Atmospheric Stability ◽  
Bending Moment ◽  
Turbulent Energy ◽  
Offshore Wind ◽  
Stability Conditions ◽  
Turbulent Wind ◽  
Base Side ◽  
Side Bending

Turbulent wind at offshore sites is known as the main cause for fatigue on offshore wind turbine components. Numerical simulations are commonly used to predict the loads and motions of floating offshore wind turbines; however, the definition of representative wind input conditions is necessary. In this study, the load and motion responses of a spar-type Offshore Code Comparison Collaboration (OC3) wind turbine under different turbulent wind conditions is studied and investigated by using SIMO-Riflex in Simulation Workbench for Marine Applications (SIMA) workbench. Using the two spectral models given in the International Electrotechnical Commission (IEC) standards, it is found that a lower wind lateral coherence under neutral atmospheric stability conditions results in an up to 27% higher tower base side–side bending moment and a 20% higher tower top torsional moment. Comparing different atmospheric stability conditions simulated using a spectral model based on FINO1 wind data measurement, the highest turbulent energy content under very unstable conditions yields a 26% higher tower base side–side bending moment and a 27% higher tower top torsional moment than neutral conditions, which have the lowest turbulent energy content and turbulent intensity. The yaw-mode of the OC3 wind turbine is found to be the most influenced component by assessing variations in both the lateral coherence and the atmospheric stability conditions.

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.

Numerical Study of Yawed Wind Turbine Under Unstable Atmospheric Boundary Layer Flows

2020 ◽  
Author(s):  
Dezhi Wei ◽  
Decheng Wan
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Wind Turbine ◽  
Numerical Study ◽  
Atmospheric Stability ◽  
Wind Farms ◽  
Total Power ◽  
Turbulent Structures ◽  
Ambient Turbulence ◽  
Turbine Wake

Abstract Turbine-wake interactions among wind turbine array significantly affect the efficiency of wind farms. Yaw angle control is one of the potential ways to increase the total power generation of wind plants, but the sensitivity of such control strategy to atmospheric stability is rarely studied. In the present work, large-eddy simulation of a two-turbine configuration under convective atmospheric boundary layer is performed, with different yaw angles for the front one, the effect of turbine induced forces on the flow field is modeled by actuator line. Emphasis is placed on wake characteristics and aerodynamic performance. Simulation results reveal that atmospheric stability has a considerable impact on the behavior of wind turbine, wake deflection on the horizontal hub height plane for yawed wind turbine is relatively small, compared with the result of the empirical wake model proposed for wind turbine operating in the neutral stratification, which is attributed to the higher ambient turbulence intensity and large variance of wind direction in the convective condition. And associated with the smaller wake deflection, the total power production does not increase as expected when yawing the upstream turbine. In addition, due to the existence of great quantities of disorganized coherent turbulent structures in the unstable condition, the yaw bearing moment experienced by the downstream wind turbine increases dramatically, even if the rotor plane of the first turbine is perpendicular to the inflow direction.

scholarly journals Wind Turbulence Statistics of the Atmospheric Inertial Sublayer under Near-Neutral Conditions

Atmosphere ◽  
2020 ◽  
Vol 11 (10) ◽  
pp. 1087
Author(s):  
Eslam Reda Lotfy ◽  
Zambri Harun
Keyword(s):  
Boundary Layer ◽  
Atmospheric Stability ◽  
Turbulent Velocity ◽  
Stability Conditions ◽  
Mean Velocity ◽  
Law Of The Wall ◽  
Turbulent Statistics ◽  
The Mean ◽  
The Law ◽  
Velocity Variances

The inertial sublayer comprises a considerable and critical portion of the turbulent atmospheric boundary layer. The mean windward velocity profile is described comprehensively by the Monin–Obukhov similarity theory, which is equivalent to the logarithmic law of the wall in the wind tunnel boundary layer. Similar logarithmic relations have been recently proposed to correlate turbulent velocity variances with height based on Townsend’s attached-eddy theory. The theory is particularly valid for high Reynolds-number flows, for example, atmospheric flow. However, the correlations have not been thoroughly examined, and a well-established model cannot be reached for all turbulent variances similar to the law of the wall of the mean-velocity. Moreover, the effect of atmospheric thermal condition on Townsend’s model has not been determined. In this research, we examined a dataset of free wind flow under a near-neutral range of atmospheric stability conditions. The results of the mean velocity reproduce the law of the wall with a slope of 2.45 and intercept of −13.5. The turbulent velocity variances were fitted by logarithmic profiles consistent with those in the literature. The windward and crosswind velocity variances obtained the average slopes of −1.3 and −1.7, respectively. The slopes and intercepts generally increased away from the neutral state. Meanwhile, the vertical velocity and temperature variances reached the ground-level values of 1.6 and 7.8, respectively, under the neutral condition. The authors expect this article to be a groundwork for a general model on the vertical profiles of turbulent statistics under all atmospheric stability conditions.

Modeling of the atmospheric boundary layer under stability stratification for wind turbine wake production

2019 ◽  
pp. 0309524X1988092
Author(s):  
Mohamed Marouan Ichenial ◽  
Abdellah El-Hajjaji ◽  
Abdellatif Khamlichi
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Large Scale ◽  
Wind Farm ◽  
Layer Structure ◽  
Atmospheric Stability ◽  
Weather Conditions ◽  
Boundary Layer Structure

The assessment of climatological site conditions, airflow characteristics, and the turbulence affecting wind turbines is an important phase in developing wake engineering models. A method of modeling atmospheric boundary layer structure under atmospheric stability effects is crucial for accurate evaluation of the spatial scale of modern wind turbines, but by themselves, they are incapable to account for the varying large-scale weather conditions. As a result, combining lower atmospheric models with mesoscale models is required. In order to realize a reasonable approximation of initial atmospheric inflow condition used for wake identification behind an NREL 5-MW wind turbine, different vertical wind profile models on equilibrium conditions are tested and evaluated in this article. Wind farm simulator solvers require massive computing resources and forcing mechanisms tendencies inputs from weather forecast models. A three-dimensional Flow Redirection and Induction in Steady-state engineering model was developed for simulating and optimizing the wake losses of different rows of wind turbines under different stability stratifications. The obtained results were compared to high-fidelity simulation data generated by the famous Simulator for Wind Farm Applications. This work showed that a significant improvement related to atmospheric boundary layer structure can be made to develop accurate engineering wake models in order to reduce wake losses.

scholarly journals A BEM-Based Actuator Disk Model for Wind Turbine Wakes Considering Atmospheric Stability

2019 ◽  
Author(s):  
Xing Xing Han ◽  
De You Liu ◽  
Chang Xu ◽  
Wen Zhong Shen ◽  
Lin Min Li ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Wind Farm ◽  
Atmospheric Stability ◽  
Stability Conditions ◽  
High Fidelity ◽  
Thrust Coefficient ◽  
Disk Model ◽  
Similarity Functions ◽  
Actuator Disk ◽  
Blade Element

Atmospheric stability affects wind turbine wakes significantly. High-fidelity approaches such as large eddy simulations (LES) with the actuator line (AL) model which predicts detailed wake structures, fail to be applied in wind farm engineering applications due to its expensive cost. In order to make wind farm simulations computationally affordable, this paper proposes a new actuator disk model (AD) based on the blade element method (BEM) and combined with Reynolds-averaged Navier–Stokes equations (RANS) to model turbine wakes under different atmospheric stability conditions. In the proposed model, the upstream reference velocity is firstly estimated from the disk averaged velocity based on the one-dimensional momentum theory, and then is used to evaluate the rotor speed to calculate blade element forces. Flow similarity functions based on field measurement are applied to limit wind shear under strongly stable conditions, and turbulence source terms are added to take the buoyant-driven effects into consideration. Results from the new AD model are compared with field measurements and results from the AD model based on the thrust coefficient, the BEM-AD model with classical similarity functions and a high-fidelity LES approach. The results show that the proposed method is better in simulating wakes under various atmospheric stability conditions than the other AD models and has a similar performance to the high-fidelity LES approach however in much lower computational cost.

Wake Measurements Around Operating Wind Turbines

1985 ◽  
Vol 107 (2) ◽  
pp. 183-185 ◽  
Author(s):  
R. W. Baker ◽  
S. N. Walker ◽  
P. C. Katen
Keyword(s):  
Wind Turbine ◽  
Atmospheric Stability ◽  
Vertical Axis ◽  
Operating Conditions ◽  
Horizontal Axis ◽  
Stability Conditions ◽  
State University ◽  
Vertical Axis Wind Turbine ◽  
Oregon State University ◽  
Velocity Deficits

Researchers at Oregon State University have conducted wind measurement programs to describe the wake behind large horizontal axis turbines at Goodnoe Hills, Washington, (MOD-2), and behind the FloWind vertical axis wind turbine near Ellenburg, Washington. Wake measurements were taken using portable kite anemometers as well as fixed place anemometers under several atmospheric stability conditions and turbine operating conditions. Centerline hub height (midrotor) measurements were taken downwind and crosswind from 3–9 diameters. These wake programs are discussed and the velocity deficits measured are compared to the estimated deficits calculated from wake models.

scholarly journals Evaluation of tilt control for wind-turbine arrays in the atmospheric boundary layer

2021 ◽  
Vol 6 (3) ◽  
pp. 663-675
Author(s):  
Carlo Cossu
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Wind Turbine ◽  
Boundary Layers ◽  
High Speed ◽  
Large Scale ◽  
Passive Control ◽  
Vertical Wind Shear ◽  
Large Power ◽  
Turbine Arrays

Abstract. Wake redirection is a promising approach designed to mitigate turbine–wake interactions which have a negative impact on the performance and lifetime of wind farms. It has recently been found that substantial power gains can be obtained by tilting the rotors of spanwise-periodic wind-turbine arrays. Rotor tilt is associated with the generation of coherent streamwise vortices which deflect wakes towards the ground and, by exploiting the vertical wind shear, replace them with higher-momentum fluid (high-speed streaks). The objective of this work is to evaluate power gains that can be obtained by tilting rotors in spanwise-periodic wind-turbine arrays immersed in the atmospheric boundary layer and, in particular, to analyze the influence of the rotor size on power gains in the case where the turbines emerge from the atmospheric surface layer. We show that, for the case of wind-aligned arrays, large power gains can be obtained for positive tilt angles of the order of 30∘. Power gains are substantially enhanced by operating tilted-rotor turbines at thrust coefficients higher than in the reference configuration. These power gains initially increase with the rotor size reaching a maximum for rotor diameters of the order of 3.6 boundary layer momentum thicknesses (for the considered cases) and decrease for larger sizes. Maximum power gains are obtained for wind-turbine spanwise spacings which are very similar to those of large-scale and very-large-scale streaky motions which are naturally amplified in turbulent boundary layers. These results are all congruent with the findings of previous investigations of passive control of canonical boundary layers for drag-reduction applications where high-speed streaks replaced wakes of spanwise-periodic rows of wall-mounted roughness elements.

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