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The comprehensive examination of typhoon impacts on offshore wind power in Chinese waters, which are prone to severe typhoons, remains largely unexplored. This paper takes a step toward assessing extreme design wind conditions for offshore wind turbines in Chinese waters and investigates typhoon-induced wind conditions considering their spatiotemporal effects. For this purpose, a spatiotemporal analysis framework for typhoons was proposed that includes a data-driven typhoon wind speed field model and estimation method of the extreme wind speed. The wind speed field model introduces a measured correction coefficient to enhance the generalization across various observed typhoons, thereby accurately capturing spatiotemporal typhoon effects. The analysis framework was applied to dozens of typical worst-case scenarios of typhoons passing through offshore wind farms in Chinese waters. These scenarios were selected based on typhoon observation data from the past 30 years. The quantitative analysis assesses and discusses the spatiotemporal impacts of typhoons on the mean wind speed, fluctuating wind speed, extreme wind speed, peak factor, and gust factor. The results indicate significant spatiotemporal impacts of typhoons on the inflow wind speed field. The maximum gust wind speed difference could exceed tenfold at various times or for different turbines. This study offers an interpretation of why wind turbines within the same wind farm may experience varying degrees of damage during identical typhoon attacks. By examining the spatiotemporal variation characteristics of typhoons and the corresponding induced wind speed fields, this paper highlights the significance of these factors for typhoon-resistant design in offshore wind farms, thus aiding in ensuring the structural safety of offshore wind turbines. [ABSTRACT FROM AUTHOR]

The wake of a wind turbine has an important influence on the output power of wind farms. Staggered height layout is an emerging method for the layout optimization of wind farms. In order to study the effect of a staggered height layout on the overall power output of wind farms in depth, we established a combination of two large wind turbines and three small wind turbines arranged laterally between the two large wind turbines, and set four working conditions with different distances between the small wind turbines and the downstream large wind turbines as the research objects. The wind turbine array is analyzed by numerical simulation The layouts add three small wind turbines between the two large wind turbines, and each row of small wind turbines has a different distance from the downstream large wind turbines. The results show that as the distance from the upstream large wind turbine increases, the power of the three small wind turbines on the downstream wind turbine tends to be positive. The numerical simulation suggests that under the inflow wind speed, the closer to the downstream large wind turbine, the higher the wind speed is at the hub height. [ABSTRACT FROM AUTHOR]

With the increasing construction of large-scale wind turbines in seismically active coastal areas, the survivability of these high-rated-power offshore wind turbines (OWTs) in marine and geological conditions becomes extremely important. Although research on the dynamic behaviors of OWTs under earthquakes has been conducted with consideration of the soil-structure interaction, the attention paid to the impact of earthquake-induced seabed liquefaction on OWTs supported by large-diameter monopiles remains limited. In view of this research gap, this study carries out dynamic analyses of a 10 MW OWT under combined wind, wave, and earthquake loadings. This study uses a pressure-dependent multisurface elastoplastic constitutive model to simulate the soil liquefaction phenomenon. The results indicate that the motion of the large-diameter monopile leads to more extensive soil liquefaction surrounding the monopile, specifically in the zone near the pile toe. Moreover, compared with earthquake loading alone, liquefaction becomes more severe under the coupled wind and earthquake loadings. Accordingly, the dynamic responses of the OWT are apparently amplified, which demonstrates the importance of considering the coupling loadings. Compared with wind loading, the effect of wave loading on the dynamic response and liquefaction potential is relatively insignificant. [ABSTRACT FROM AUTHOR]

In a large wind farm, the wakes of upstream and downstream wind turbines can interfere with each other, affecting the overall power output of the wind farm. To further improve the numerical accuracy of the turbine wake dynamics under atmosphere turbulence, this work proposes some improvements to the actuator line-large-eddy simulation (AL-LES) method. Based on the dynamic k-equation large-eddy simulation (LES), this method uses a precursor method to generate atmospheric inflow turbulence, models the tower and nacelle wakes, and improves the body force projection method based on an anisotropic Gaussian distribution function. For these three improvements, three wind tunnel experiments are used to validate the numerical accuracy of this method. The results show that the numerical results calculated in the far-wake region can reflect the characteristics of typical onshore and offshore wind conditions compared with the experimental results. After modeling the tower and nacelle wakes, the wake velocity distribution is consistent with the experimental result. The radial migration velocity of the tip vortex calculated by the improved blade body force distribution model is 0.32 m/s, which is about 6% different from the experimental value and improves the prediction accuracy of the tip vortex radial movement. The method proposed in this paper is very helpful for wind turbine wake dynamic analysis and wind farm power prediction. [ABSTRACT FROM AUTHOR]

Abstract Blade yaw will change aerodynamic performance of large-scale wind turbine structure, especially under rainstorm conditions. Structural responses and stability of large-scale wind turbine system during rainstorm are more complicated due to the impact force of rainstorm on the structural surface and its influences on the incoming turbulence. In this study, the 5 MW wind turbine tower-blade system which was developed by Nanjing University of Aeronautics and Astronautics (NUAA) was used as the research object. Firstly, the surrounding wind field of the 5 MW wind turbine tower-blade system under different yaw angles (0°, 5°, 10°, 20°, 30° and 45°) was simulated by the computational fluid dynamics (CFD) technology based on the wind-rain two-way coupling algorithm. Secondly, the wind-rain coupling synchronous iteration was carried out by adding the discrete phase model (DPM). Based on numerical simulation results, the influencing law of yaw angle on wind-driven rainfall, additional acting force of raindrops and rain-induced pressure coefficient was discussed. The velocity flow line, turbulence energy strength, raindrop running speed and trajectory action mechanism on the structural surface in wind-rain coupling field was disclosed. Moreover, the distribution laws and fitting formula of wind-rain equivalent pressure coefficient under different yaw angles were constructed. Finally, large-scale wind turbine tower-blade coupling model under different yaw angles was constructed by combining the finite element method. Structural responses, buckling stability and ultimate bearing capacity of the large-scale wind turbine system with considerations to different yaw angles under wind condition and wind-rain condition were discussed. Results demonstrated that yaw angle can affect aerodynamic force and comprehensive stress performance of the wind turbine system significantly. The wind-rain load enhances structural responses of the system, and decreases the overall buckling stability and ultimate bearing capacity of the wind turbine. Main conclusions not only can provide references for accurate load evaluation under extreme complex conditions, but also are conducive to deepen understandings on the action mechanism of wind-rain load. Highlights • An effective numerical method was developed to predict aerodynamic loads under yaw and wind-rain combination condition. • The mechanism of flow field under wind and rain loads was revealed. • The equivalent load model with yaw of wind-rain condition was established. • The buckling stability and ultimate bearing capacity underwind-rain condition were investigated. [ABSTRACT FROM AUTHOR]

The current work describes a novel technique for wind turbine rotor optimization. The aerodynamic design and optimization of wind turbine rotor can be achieved with different methods, such as the semi-empirical engineering methods and more accurate computational fluid dynamic (CFD) method. The CFD method often provides more detailed aerodynamics features during the design process. However, high computational cost limits the application, especially for rotor optimization purpose. In this paper, a CFD-based actuator disc (AD) model is used to represent turbulent flow over a wind turbine rotor. The rotor is modeled as a permeable disc of equivalent area where the forces from the blades are distributed on the circular disc. The AD model is coupled with a Reynolds Averaged Navier-Stokes (RANS) solver such that the thrust and power are simulated. The design variables are the shape parameters comprising the chord, the twist and the relative thickness of the wind turbine rotor blade. The comparative aerodynamic performance is analyzed between the original and optimized reference wind turbine rotor. The results showed that the optimization framework can be effectively and accurately utilized in enhancing the aerodynamic performance of the wind turbine rotor. [ABSTRACT FROM AUTHOR]

In the areas prone to severe typhoons, such as the south and southeast China waters, offshore wind turbine design will most likely fall into Class-S, but the current design standards have not treated much detail on the technical parameters under the typhoon-induced conditions to guide the structural design. This study set out to investigate the feasibility of extreme wind conditions in existing standards for offshore wind turbines in the south and southeast China waters. The extreme wind conditions in existing standards and actual typhoon cases in the south and southeast China waters were used to compare and analyze the typhoon-induced wind effect on offshore wind turbines. This study supports evidence from previous views that the extreme wind condition specified by existing design standards does not provide a sufficient safety margin for the south and southeast China waters use. Another interesting finding is that from the perspective of the typhoon-resistant design of large-scale offshore wind turbines in the future, it is more inclined to abandon the height of the hub and use the height of 10m as the reference wind speed height to obtain a more reasonable wind speed field as input conditions. The insights gained from this study may be of assistance to the typhoon-resistant design of customized offshore wind turbines in the south and southeast China waters and would help reduce the risks and economic losses of Class-S wind turbines in other typhoon-prone areas. [ABSTRACT FROM AUTHOR]

The theoretical system of existing civil engineering typhoon models is too simplified and the simulation accuracy is very low. Therefore, in this work a meso-scale weather forecast model (WRF) based on the non-static Euler equation model was introduced to simulate typhoon "Nuri" with high spatial and temporal resolution, focusing on the comparison of wind direction and wind intensity characteristics before, during and after the landing of the typhoon. Moreover, the effectiveness of the meso-scale typhoon "Nuri" simulation was verified by a comparison between the track of the typhoon center based on minimum sea level pressure and the measured track. In this paper, the aerodynamic performance of large wind turbines under typhoon loads is studied using WRF and CFD nesting technology. A 5 MW wind turbine located in a wind power plant on the southeast coast of China has been chosen as the research object. The average and fluctuating wind pressure distributions as well as airflow around the tower body and eddy distribution on blade and tower surface were compared. A dynamic and time-historical analysis of wind-induced responses under different stop positions was implemented by considering the finite element complete transient method. The influence of the stop position on the wind-induced responses and wind fluttering factor of the system were analyzed. Finally, under a typhoon process, the most unfavorable stop position of the large wind turbine was concluded. The results demonstrated that the internal force and wind fluttering factor of the tower body increased significantly under the typhoon effect. The wind-induced response of the blade closest to the tower body was affected mostly. The wind fluttering factor of this blade was increased by 35%. It was concluded from the analysis that the large wind turbine was stopped during the typhoon. The most unfavorable stop position was at the complete overlapping of the lower blade and the tower body (Condition 1). The safety redundancy reached the maximum when the upper blade overlapped with the tower body completely (Condition 5). Therefore, it is suggested that during typhoons the blade of the wind turbine be rotated to Condition 5. [ABSTRACT FROM AUTHOR]

Noise pollution from wind turbines has been receiving significant attention with the rapid increase in global wind power installation, especially in urban environments where population density is high. Several countries tried to quantify the relation between wind turbine design characteristics and noise impact levels. To date, no quantitative results have been presented, while it is believed that the vertical axis wind turbine has advantages compared to horizontal axis wind turbines in certain applications. With the purpose to enhance understanding of noise pollution caused by vertical axis wind turbines in the urban environment, a systematic experimental test campaign in an anechoic wind tunnel was conducted. The results demonstrate that low-frequency noise increasingly affects humans when the wind speed increases. The blade-passing frequency is identified as a major parameter in the generation of low-frequency noise. More importantly, the noise pollution from various designs is discussed to analyze the impacts on humans and various animals. These designs are analyzed according to national standards from different countries. It is found that an optimal design of a vertical axis wind turbine is suitable for the urban environment with minimal noise impact. • Noise of vertical axis wind turbines is studied experimentally in a systematic way. • The impact level of low-frequency noise increases as the wind speed increases. • The blade-passing frequency is a major parameter in the low-frequency noise. • Optimal design philosophies are recommended based on different urban environments. [ABSTRACT FROM AUTHOR]

Copyright of Transactions of Nanjing University of Aeronautics & Astronautics is the property of Editorial Department of Journal of Nanjing University of Aeronautics & Astronautics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• • Compressibility effects of the IEA-15 MW wind turbine are examined. • • Compressibility effects have a significant effect on aerodynamic of the large wind turbine. • • A detailed analysis the compressible results for the tip airfoil and the rotor is presented. • • The compressibility effects on the wake of the IEA-15 MW turbine are discussed. • • Validations of the numerical method against experimental data are performed. With the gradual upscaling of offshore wind turbines, the blade size becomes large and the blade tip velocity reaches almost a Mach number of 0.3, the limit of the incompressible flow assumption. To simulate wind turbine flows, an incompressible solver was often a good choice as it gave good predictions and the Mach number of the wind turbine flows were small. When the Mach number is increased to be close to 0.3, the validity of incompressible flow may be questionable and thus needs to be checked. In this paper, an accurate wind turbine flow solution method is proposed to study the compressibility effects. First, the National Renewable Energy Laboratory (NREL) Phase VI wind turbine is used as an example to verify the method at a small Mach number. Through a comparative analysis between the compressible, the incompressible numerical results, and experimental data, the proposed method is found with a good simulation accuracy. Next, the flow fields of the large wind turbine IEA-15 MW, under different wind conditions are simulated. The local Mach number, density and pressure coefficient at different blade cross-sections of the compressible results are analyzed and compared to its incompressible ones, and the influences of compressibility on the thrust, torque and power of the wind turbine are quantified. The results show that at the rated wind speed, the thrust of the compressible flow simulation is 1.40 % higher than that of the incompressible one, and the torque of the compressible flow simulation is nearly 11.07 % higher than that of the incompressible one. As a result, the compressibility effects are recommended to be added in future studies of large wind turbines. [ABSTRACT FROM AUTHOR]

Copyright of Transactions of the Chinese Society of Agricultural Engineering is the property of Chinese Society of Agricultural Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Transactions of the Chinese Society of Agricultural Engineering is the property of Chinese Society of Agricultural Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)