Wind Yaw Research Articles

Ride comfort assessment of road vehicles on a long-span truss girder suspension bridge under crosswinds

The precise identification of the aerodynamic loads on vehicles is a fundamental concern in assessing the ride comfort of vehicles crossing long-span bridges in the presence of strong crosswinds. However, the consideration of aerodynamic interference between vehicles and truss girder bridges is limited in existing studies. Furthermore, in practical engineering, wind barriers are commonly installed to enhance the ride comfort of vehicles crossing long-span bridges, but previous studies have primarily focused on the impact of wind barriers on the aerodynamic coefficients and dynamic responses of vehicles. This paper focuses on the aerodynamic interaction between trucks and truss girder bridges, through wind tunnel testing. The aerodynamic coefficients of the vehicle with three different ventilation ratios and four different heights of wind barriers were obtained. The dynamic response of road vehicles on a truss girder suspension bridge with a main span of 965 m was numerically calculated using the coupled analysis of wind-vehicle-bridge system and measured aerodynamic coefficients considering aerodynamic interference. On this basis, the comfort of road vehicles was investigated with different section types of the girder and different wind barrier parameters, and it was evaluated accordance with the overall vibration total value (OVTV) recommended in the ISO 2631–1. It is found that the aerodynamic coefficients of road vehicles are sensitive to the type of wind barrier. Wind barriers can reduce the road vehicle’s aerodynamic loads at high wind yaw angles. Wind barriers can also improve the ride comfort of road vehicles on the long-span truss girder suspension bridge.

Similarities in the meandering of yawed rotor wakes

This study investigated the meandering of yawed wind turbine rotor wakes, focusing on the similarities across different yaw angle scenarios. Spectrum analysis of velocity fluctuations reveals that the meandering of the yawed rotor wake is symmetrical about the wake center, despite its skewness. The non-zero lateral force of the yawed rotor enhances meandering in the lateral direction compared to the vertical direction. However, the lateral profiles of meandering strength exhibit similarities across different yaw angle scenarios, indicating a consistent wake meandering mode. The wake meandering frequency increases with the yaw angle. A relationship involving wake meandering frequency, drag coefficient, and yaw angle is formulated for wind turbine rotor wakes under different yaw angles. This relationship is also applicable to thin plate wakes within a certain range of inclination angles/yaw angles. The present study reveals the similarity in wake meandering characteristics across different yaw angle scenarios, which is instrumental in improving our understanding of wake meandering and in developing analytical wake models for wind turbines.

A novel improved actuator line method for tandem-arranged wind turbines wake analysis and its application

For a typical wind farm layout, the disturbance caused by wind turbine wakes typically exerts a significant negative impact on power generation. However, due to the insufficient reliability of existing multiple turbines wake simulations, the improved effects of wind farm layout modifications cannot be fully verified. In this paper, we employ a high-fidelity model, the Improved Actuator Line Model (I-ALM), combined with Large Eddy Simulation (LES) based on the OpenFOAM solver, to investigate the active yaw strategy of wind farms. The improvements in the ALM primarily include the Gaussian anisotropic force projection method, the integral velocity sampling method, and the enhanced nacelle-tower projection method. Firstly, we conduct numerical simulations of the NTNU "Blind Test" experimental cases using the combination of the I-ALM method and LES, mainly focusing on aerodynamic forces and wake development characteristics. Then, the proposed method is applied to the wake prediction of three NREL 5 MW tandem-arranged yaw wind turbines after benchmarking. The power generation and wake characteristics under different yaw angles is comprehensively predicted, leading to the development of a preliminary active yaw strategy (including rated state and maximum TSR state). This strategy holds significant guiding value for the accurate and efficient simulation of wind farms.

Experimental study of vortex-induced vibration of stay cables installed with two types of perforated shroud light devices

To address both illumination issues and the common vortex-induced vibration (VIV) of bridge cables, a perforated shroud light device is proposed. The effect of the different porosities (20%, 35%, 42%, and 55%) on VIV of the rigid segmented shroud cable models is studied first by wind tunnel tests. It reveals that shrouds with porosities of 20% and 35% could reduce the VIV amplitude of the smooth cables by 26% and 46%, respectively. However, shrouds with porosities of 42% and 55% tend to increase the complexity and risk associated with VIV. Vibration measurements on flexible should cable with 20% porosity were conducted for both vertical and inclined models with an inclination of 35° and yaw angles of 0°, 30° and 60°. Shrouds with a porosity of 20% exhibit similar effects on vertical flexible cables as on horizontal rigid cables, in both cases mitigating VIV. The impact on the inclined flexible cables depends on the yaw angle. At the yaw angle of 0°, the shroud effectively mitigates VIV in flexible cables. However, at yaw angles of 30° and 60°, the same porosity level shroud exacerbates the risk of VIV in the inclined flexible cable. This may be due to the enhanced wind velocity along the cable axial direction and decreased penetrating flow rate through the shroud as the wind yaw angle increases. Overall, it was found that a shroud with a porosity of 20%–35% performed the best and was recommended for applications on cables with no inclination and inclined cable at yaw angle β = 0°.

Aerodynamic characteristics of the train under the stationary thunderstorm downburst wind

The aerodynamic characteristics of the train under the stationary thunderstorm downburst wind were studied. The thunderstorm downburst wind test device was employed to simulate the thunderstorm downburst wind field. Based on the rigid model pressure measurement tests, analyses were conducted on the influence of radial distance on the pressure coefficients on the train surface, the aerodynamic load coefficients of the train section, and the total force coefficients of the middle and head cars. On this basis, combined with the computational fluid dynamics model, further exploration was conducted on the characteristics of the mean pressure on the train surface and the flow field around the train at different radial distances under the stationary thunderstorm downburst wind. The research results show that the train's total aerodynamic coefficients fluctuate with the train's position. The non-uniform distribution of the lateral force coefficient for each train section is primarily caused by variations in the wind yaw angle along the train's longitudinal axis. Variations in the wind attack angle at different radial distances cause the total lateral force coefficient to change accordingly. When the radial distance r/Dj = 0.5, there is no significant vortex-shedding phenomenon in the flow field around the train. However, when radial distance r/Dj = 1 and 1.5, the leeward surface exhibits a regular vortex-shedding phenomenon. Vortex shedding starts at the junction of the leeward surface and the top surface, extending from the middle car along the train's longitudinal axis toward the front and rear.

Dynamic Response Analysis of Moving Trains Passing Through the Stationary Thunderstorm Downburst Wind

The safety of the high-speed train traveling through the stationary thunderstorm downburst wind was studied. First, a thunderstorm wind test device was used to simulate the stationary thunderstorm downburst wind. Based on the rigid model pressure measurement tests, the aerodynamic forces of the train traveling along different paths through the stationary thunderstorm downburst wind were measured. The influence of the radial distance of the crossing path on the aerodynamic force coefficients of the train was investigated. On this basis, an unsteady aerodynamic model of the high-speed train crossing through the stationary thunderstorm downburst wind was established, and dynamic response analysis was carried out using the SIMPACK multibody dynamics simulation software to explore further the safety of the high-speed train crossing through the stationary thunderstorm downburst wind. The research showed that the stationary thunderstorm downburst wind field has significant spatial variation characteristics compared with the atmospheric boundary layer wind field. When the train passes through the thunderstorm downburst wind, the radial wind speed and wind yaw angle experienced by the train constantly change, and the change curve shows a symmetrical distribution. The aerodynamic force of the train will undergo sudden loading and unloading processes, and the lateral force coefficient of the train on different paths shows a “pulse-type” variation. Moreover, the lateral force coefficient increases with the increase of wind yaw angle. Under the influence of the thunderstorm downburst wind, the variation trend of the aerodynamic force coefficients of the train is consistent with that under crosswind. However, there are significant differences in the numerical values. Therefore, it is impossible to simply use the formula for calculating the aerodynamic force coefficients of the train under crosswinds to predict the aerodynamic force coefficients of the train under the thunderstorm downburst wind. While passing through the thunderstorm downburst wind, the overturning coefficient index plays a decisive role in the safety of train operations. Train rollover is the main form of train safety accidents, while derailment accidents are not easy. The numerical results obtained in this study are significant for evaluating the operational safety while moving trains traversing the stationary thunderstorm downburst wind.

Dynamic individual pitch control for wake mitigation: Why does the helix handedness in the wake matter?

Wind farm flow control aims at mitigating wake effects in order to maximize power production in wind farms. This work mostly focuses on the Helix strategy, which relies on individual pitch control to radially offset the application point of the thrust force from the rotor center and to dynamically change its azimuthal position. Previous studies have shown that power gains for a downstream turbine are higher for a counter-clockwise (CCW) rotation of the application point than for a clockwise (CW) one. In the CCW case, the wake develops as a right-handed helix, while in the CW case, a left-handed helix is observed. Using Large Eddy Simulations, this paper shows that the helix handedness in the wake matters due to its interaction with the wake swirl. Results of the CCW and CW helix first highlight the formation of streamwise vorticity in the near wake, which is transformed into strong coherent vortices in the far wake. Those vortex structures, to some extent similar to the counter-rotating vortex pair in the wake of yawed wind turbines, are responsible for (i) displacing the wake thanks to their induced velocities and (ii) deforming the shape of the wake.

A new analytical wind turbine wake model considering the effects of coriolis force and yawed conditions

Wind turbine wakes significantly affect power production and impose higher loads on downstream turbines. Therefore, the development of accurate and efficient wake models is important for optimizing wind farm layouts and predicting wind turbine performance. This study introduces a novel analytical wake model for yawed wind turbines that incorporates the effects of the Coriolis force. The wake deflection in the far wake region is derived through the application of the principles of mass and momentum conservation. In the near wake, the deflection is assumed to be linear with distance. A Gaussian distribution is assumed for the velocity deficit within the wind turbine wake. Two approaches have been proposed to estimate the onset of the far wake region. While the first approach employs a simplified empirical formula, the second approach utilizes an iteration-based method. The proposed analytical wake model has been validated against computational fluid dynamics (CFD) results. Subsequently, the effects of several important parameters on the wake deflection have been systematically investigated. Overall, the simulation results showed a satisfactory agreement between the CFD results and those obtained from the proposed model. Furthermore, the study concluded that the Coriolis force can exert significant effects on wake deflection, particularly in the far wake region, confirming previous findings from numerical simulations. Due to its simplicity and computational efficiency, the proposed model can be readily used in several applications, including wind farm layout optimization, control and risk assessment.

Buffeting characteristics of cable-stayed box beam bridge based on pressure measurement test of full bridge aeroelastic model

The aim of this study is to explore the buffeting characteristics of cable-stayed box beam bridge based on pressure measurement test of full bridge aeroelastic model. The study includes the influence of turbulence integral length scale and wind yaw angle on the magnitude of buffeting force, spatial distribution of buffeting force, and buffeting displacement response. Under larger turbulence integral length scale, the buffeting force of the box beam and it’s spanwise correlation are larger, which verifies the three-dimensional effect of the buffeting force. It is worth mentioning that, unlike traditional section models, there are differences in the pressure values of the pressure strips in the aeroelastic model at the flow separation point, which may be influenced by the cables. The experimental results of different wind yaw angles show that there is little difference in the buffeting force of the box beam section under the condition of 0°∼15° wind yaw angle, indicating that the maximum buffeting response will occur in the range of 0°∼15° wind yaw angle, which is consistent with the displacement results measured by the aeroelastic model. In addition, by fixing the model with a steel wire, the static and vibration states of the model were achieved. However, due to the high stiffness of the model, it can only generate small buffeting displacement, and the self-excited force component can be almost ignored. There is no significant difference in the results between the static and vibration states.

Wake measurement of wind turbine under yawed conditions using UAV anemometry system

This study employs a UAV anemometry system to assess the wind field around a yawed wind turbine, particularly focusing on its wake during operational conditions. The research findings reveal that the evolution of wind turbine wakes follows distinct patterns at various downstream distances. Turbulence intensity notably amplifies within regions characterized by significant fluctuations in mean wind speed. Specifically, in yawed conditions, the areas with the highest turbulence generated by the rotor coincide with zones exhibiting pronounced variations in mean wind speed. The heightened turbulence within the wake region to some extent constrains the safety and economic viability of wind farms. Turbulence intensity increases significantly in the region where the average wind speed changes greatly, that is, under the yaw state of the wind turbine, this region is characterized with the strongest turbulence generated by the rotor. The UAV anemometry system's wind speed assessment closely matches predictions from the Y-3DJGF model, accounting for wake experience coefficient adjustments. Furthermore, in yaw conditions, the wind turbine's wake trajectory exhibits some deviation from the incident flow's direction, with an initial increase in slope followed by gradual stabilization. As the downstream distance increases, the trajectory will eventually establish a consistent trend with the incident flow. The cost-effective and flexible UAV anemometry system enhances wind field measurements, offering an innovative approach for wind energy sector research and engineering.

Time-domain fatigue damage assessment for wind turbine tower bolts under yaw optimization control at offshore wind farm

Yaw optimization control is recognized as the most effective active wake control strategy for enhancing the overall power generation of wind farms. However, the potential adverse effects of yaw optimization control on the fatigue life of wind turbines remain unclear. This study examined the effect of yaw optimization control on the fatigue life of offshore wind turbines using tower bolts. Initially, the yaw misalignment of the wind turbines was optimized using the open-source FLORIS package to maximize wind farm power generation. Subsequently, the time-varying load of the wind turbines was obtained through the OpenFAST software, using the optimal yaw misalignment, wind speed, and turbulence intensity at the hub height as inputs. The fatigue life of the wind turbines was then calculated by integrating the Schmidt–Neuper engineering stress algorithm, rain flow counting method, and Miner-Palmgren fatigue damage accumulation theory. Finally, a case study of the Horns Rev I large-scale offshore wind farm, comprising 80 wind turbines, revealed that yaw optimization control could significantly enhance the annual power generation of the wind farm by approximately 1.818%. However, optimization comes at the cost of reducing the fatigue life of wind turbine tower bolts by approximately 3–9 years.

Influence of wind gusts on aeroelastic loads of NREL 5MW wind turbine

This study employs blade-resolved computational fluid dynamics simulations to investigate the aero-elastic loads on a yawed NREL 5MW wind turbine subject to full and partial wind gusts. A novel spatial gust representation, tailored towards application to large eddy simulations, is introduced. This methodology permits the injection of gusts with customizable spatial dimensions inside the flow domain. Simulations are conducted with gusts having the same diameter as the turbine rotor, half rotor diameter, and asymmetric impact with respect to the center of rotation of the turbine. Simulations of the turbine under yawed conditions are also considered. The flow characteristics are reported using contours and iso-surfaces of velocity magnitude and Q-criteria. Insights into the load characteristics of the turbine are described using torque, thrust, and root bending moments. This research highlights that partial gust impact contributes to noteworthy load fluctuations and blade tip deformations, stemming from the imbalance in force distribution across the rotor plane.

Full-scale aerodynamic study on the effects of tower wind shields and road-sign gantries on passing high-sided vehicles in the tower region at the Queensferry Crossing

A novel investigation into the impact of the tower road-sign gantry and the tower shielding on double-decker buses and trucks passing by the bridge tower based on a previously validated full-scale CFD model. Two sets of simulations were conducted for comparison of aerodynamic force conditions of vehicles as they pass by the bridge tower: first group of simulations were performed including and excluding the road-sign gantry; and the second group include and exclude the tower shielding. Conditions in different traffic lanes (one on leeward side and two on windward side) considered. The effect of changes in wind yaw angle are also considered. Mechanism exploration on the variation of vehicle aerodynamic force conditions was made based on the numerical visualization of wind velocity field and pressure field. Novel results suggest that the road-sign gantry provides a sheltering effect in some circumstances, but a destabilizing effect in others. In addition, the tower shielding shows significant impact on reducing aerodynamic forces and sudden force changes of the high-sided vehicles while they are passing by the bridge tower.

Wind Speed Spectrum of a Moving Vehicle under Turbulent Crosswinds

Wind loads have become one of the key influencing factors for the running safety of vehicles and comfort of passengers. The investigation of the wind speed spectrum characteristics of a moving vehicle under turbulent crosswinds is of great importance. Expressions of the wind speed spectrum of a moving vehicle were obtained from the von Kármán spectrum, based on Taylor’s frozen flow hypothesis. The influencing factors, including the ratio of the vehicle speed to the wind speed and wind yaw angles, were analyzed. The change rules of the wind speed spectrum peak and its corresponding frequency were also studied. The results show that the wind speed spectrum peak values of the moving vehicle were larger than those of the static vehicle. The wind speed spectrum peak values corresponding to the moving vehicle were first increased and then decreased, as the wind yaw angles increased. Some of the frequencies corresponding to the longitudinal wind speed spectrum values of the moving vehicle were smaller than those of the static vehicle. Therefore, the energy had been transferred to the lower frequency. For the moving vehicle, the frequency values corresponding to the longitudinal wind speed spectrum peak were first increased and then decreased, as the ratio of the vehicle speed to the wind speed and the wind yaw angle increased.

Quantitative assessment on fatigue damage induced by wake effect and yaw misalignment for floating offshore wind turbines

Wake interaction between floating offshore wind turbines (FOWTs) is complex and necessitates a comprehensive assessment, which is a prerequisite for the yaw misalignment control. However, existing research on the influence of the wake effect on fatigue damage still suffers from unreliable conclusions and incomplete analysis. Consequently, we aim to precisely and comprehensively evaluate the influence of the wake effect and yaw misalignment on the fatigue damage of FOWTs. Initially, FAST.Farm is employed to holistically assess the output power, motion response, and dynamic response of two semi-submersible FOWTs arranged in series under varying yaw misalignments and wind speeds. Subsequently, the fatigue damage results of tower welds are calculated and analyzed based on the damage equivalent load and the time-varying stress, respectively. Finally, extensive comparisons and summaries are made between FOWTs under different conditions on power performance, platform motions and fatigue damage. The results indicate that active yaw control of upstream wind turbines reduces their fatigue damage of tower weld while exacerbating that of downstream wind turbines. Moreover, yaw optimization control is crucial in managing the platform motion responses.

Stochastic Dynamical Modeling of Wind Farm Turbulence

Low-fidelity engineering wake models are often combined with linear superposition laws to predict wake velocities across wind farms under steady atmospheric conditions. While convenient for wind farm planning and long-term performance evaluation, such models are unable to capture the time-varying nature of the waked velocity field, as they are agnostic to the complex aerodynamic interactions among wind turbines and the effects of atmospheric boundary layer turbulence. To account for such effects while remaining amenable to conventional system-theoretic tools for flow estimation and control, we propose a new class of data-enhanced physics-based models for the dynamics of wind farm flow fluctuations. Our approach relies on the predictive capability of the stochastically forced linearized Navier–Stokes equations around static base flow profiles provided by conventional engineering wake models. We identify the stochastic forcing into the linearized dynamics via convex optimization to ensure statistical consistency with higher-fidelity models or experimental measurements while preserving model parsimony. We demonstrate the utility of our approach in completing the statistical signature of wake turbulence in accordance with large-eddy simulations of turbulent flow over a cascade of yawed wind turbines. Our numerical experiments provide insight into the significance of spatially distributed field measurements in recovering the statistical signature of wind farm turbulence and training stochastic linear models for short-term wind forecasting.

A data-driven machine learning approach for yaw control applications of wind farms

This study proposes a cost-effective machine-learning based model for predicting velocity and turbulence kinetic energy fields in the wake of wind turbines for yaw control applications. The model consists of an auto-encoder convolutional neural network (ACNN) trained to extract the features of turbine wakes using instantaneous data from large-eddy simulation (LES). The proposed framework is demonstrated by applying it to the Sandia National Laboratory Scaled Wind Farm Technology facility consisting of three 225 kW turbines. LES of this site is performed for different wind speeds and yaw angles to generate datasets for training and validating the proposed ACNN. It is shown that the ACNN accurately predicts turbine wake characteristics for cases with turbine yaw angle and wind speed that were not part of the training process. Specifically, the ACNN is shown to reproduce the wake redirection of the upstream turbine and the secondary wake steering of the downstream turbine accurately. Compared to the brute-force LES, the ACNN developed herein is shown to reduce the overall computational cost required to obtain the steady state first and second-order statistics of the wind farm by about 85%.

Mechanism analysis on wake-induced vibration of parallel hangers near a long-span suspension bridge tower

To reproduce the vibration phenomenon and explore the mechanism of parallel hangers near a suspension bridge tower based on the practical engineering, a pair of hangers in the wake of the bridge tower were taken as the research object. The influences of different wind yaw angles on the flow patterns of the bridge tower and aerodynamic characteristics of parallel hangers were investigated using the computational fluid dynamics (CFD) method. Then, based on the amplitude spectrum results, the relationship between the aerodynamic interference intensities of the tower wake and the displacements of parallel hangers were quantitatively described. Moreover, the coherence between the bridge tower and the parallel hangers were studied. Finally, based on the surface pressure distributions, energy input analysis, and wind speed characteristics, the vibration mechanism of parallel hangers near the bridge tower were explored. The results show that when the wind yaw angle is in the range of 0° ∼ −30°, the tower wake and the vortex shedding from the hangers jointly affect the aerodynamic characteristics of the hangers, which leads to the vibration displacements and movement tracks are observed as a sawtooth shape with multiple frequencies and synchronous skewed ellipses, respectively. The aerodynamic interference intensities of the bridge tower are positively correlated with the displacements of the hangers, and the peak amplitude at the wind yaw angle of −30° with strong aerodynamic interference is 35 mm, which is about 9 times that at the wind yaw angles of ±60° with weak aerodynamic interference. Moreover, at the wind yaw angles with strong aerodynamic interference, the mean wind pressure coefficients of the parallel hangers tend to be negative and their root mean square (RMS) values of wind pressure coefficient exhibit an overall upward trend compared with those at wind yaw angles with weak aerodynamic interference. Based on the analysis of energy input and wind speed characteristics, it is found that the low-frequency vortex shedding from the tower wake is the internal factor that continuously maintain the large vibrations of the parallel hangers.

Study on the buffeting response of a long-span truss arch bridge during construction based on a large-scale full bridge model wind tunnel test

The buffeting response of long-span truss arch bridges has become a key factor in the cantilever construction phase. It is essential to study the wind-resistant performance of arch bridges in typical construction stages. In this study, the buffeting displacements and buffeting forces were investigated based on a 1:40 scaled full bridge model wind tunnel test. Three wind attack angles and seven wind yaw angles were considered in the test. The test results show that the maximum lateral buffeting displacements of the cantilever end and the buckle tower top occur at a wind yaw angle between −15 and 15°. Finite-element analysis was performed to investigate the vibration mitigation measures of the arch bridge during the maximum cantilever construction stage. Finally, we propose some recommendations to alleviate the buffeting response of the buckle tower. The results of our study reveal that setting two symmetric wind resistance cables with an angle >20° between the cable direction and the vertical direction is useful in reducing the transverse buffeting displacement of the buckle tower. This study provides new insights into the buffeting response and vibration reduction of long-span truss arch bridges during cantilever construction.

Analysis of Wind Farms under Different Yaw Angles and Wind Speeds

Wind farm optimization is pivotal in maximizing energy output, reducing costs, and minimizing environmental impact. This study comprehensively explores wind farm behavior under varying wind conditions and yaw angles to achieve these objectives. The primary motivation is to optimize wind farm performance and efficiency through proper yaw adjustment in response to wind speed changes. A computational investigation using a three-by-three wind turbine array was conducted, employing large eddy simulation (LES) to evaluate wind farm performance. Nine LES cases were considered, incorporating three wind speeds (7.3 ms−1, 10.4 ms−1, and 4.3 ms−1) and three yaw angles (30°, 20°, and 0°), with nearly constant turbulence intensity (TI) at 12.0%. The impact of wind speed and yaw angles on wake characteristics and power outputs were analyzed. The findings reveal that wind speed has limited influence on wake characteristics and power outputs, except for lower wind speeds at a yaw angle of 20 degrees. These results contribute to understanding wind farm performance optimization, aiding in developing strategies to enhance energy extraction while minimizing costs and environmental implications.