Journal of Wind Engineering and Industrial Aerodynamics最新文献

An accurate assessment of the driving comfort and safety of road vehicles moving on a long-span bridge subjected to vortex-induced vibration (VIV) is essential for bridge administrators to decide whether the bridge should be closed to traffic. However, previous assessments often ignore the aerodynamic interference between the road vehicles and the bridge deck subjected to VIV. In this study, a specific wind tunnel model is developed to explore the aerodynamic interference between road vehicles and twin-box bridge deck during VIV. The vortex-induced force (VIF) and vortex-induced response (VIR) of the twin-box bridge deck and the aerodynamic forces on the vehicle were simultaneously measured. The influence of the vehicles on the VIV of the deck was investigated, and the influence of the deck vibration on the aerodynamic forces of the vehicle was also explored. The results show that the VIR and VIF of the bridge deck were generally reduced, depending on the type, position, and number of vehicles. The aerodynamic forces of vehicles could be amplified due to the deck vibration. These findings supplement the database of vehicle aerodynamic coefficients for assessing the driving comfort and safety of road vehicles moving on a long-span bridge subjected to VIV.

In this article, an arc-length continuation process is presented as an alternative to the classical p-k method to determine the pre-flutter modal properties of an aeroelastic system. The algorithm is based on a reformulation of the generalized eigenvalue problem into a set of nonhomogeneous algebraic equations and on the addition of a continuation equation. The reformulated system is then solved with several nonlinear solvers, and the performance of the resulting algorithms is compared to that of the p-k method on three examples. The analysis is performed mode-by-mode, initiated from wind-off conditions and gradually progressing until aeroelastic instability. The research findings highlight the efficiency of continuation methods, thanks to their ability to refine the wind speed mesh where the system experiences local variations related to rapid aeroelastic changes. The various versions of the proposed algorithm show faster convergence than the direct approach, but also excellent stability performance even in critical regimes. Finally, the mode-by-mode solution allows the use of a custom wind speed mesh for each mode separately and prevents mode swapping.

Research in cycling aerodynamics is performed using mannequins of different geometries, which are usually not shared, thus hampering the advancement of our understanding of the flow around a rider on the bike. The primary outcome of this work is to introduce and openly share two anthropometrically realistic generic cyclist models, one in time-trial and one in sprint position. These two models are obtained by averaging the scans of 14 male elite cyclists. The average cyclist geometries are published and openly accessible, making them unique in the field of cycling aerodynamic research. The second objective of this work is to better understand how the difference between the sprint and time-trial position affects the velocity and vortex topology in the wake of a cyclist and, in turn, the aerodynamic drag. Robotic volumetric particle image velocimetry measures the time-average velocity for each mannequin within a wind tunnel. One meter downstream of the lower back, the wakes of the two mannequins are dominated by strong hip/thigh streamwise counter-rotating vortices, which induce a downwash behind the riders’ backs. The strength of these vortices downstream of the sprint model is significantly larger than that of the vortices of the mannequin in the time-trial position. The same holds for a secondary vortex pair that originates from the upper arms and hips. In addition to the vortex strength, the aerodynamic drag area of the sprint model exceeds that of the time-trial model. Hence, it is presumed that stronger vortices relate to higher aerodynamic drag. In contrast to the drag area, the drag coefficient of the two models is the same. Further research is necessary to understand the relation between the cyclist position, the flow topology and the drag coefficient. Finally, the flow around the time-trial model is described in further detail to understand the origin of the different vortex structures. Through comparison to the literature, a vortex topology classification is postulated for the mid-wake and upper-wake. The arm spacing and shoulder width play a critical role in the development of this vortex system.

A 1:5 scale realistic car model of the original Twingo GT but presenting a flat underbody and no exhaust line is tested in a wind tunnel at Reynolds numbers $Re=2.15\times 10^5$ to $4.3\times 10^5$. A range of underbody flow characteristic velocities $U_b=\left(0.5-0.72\right)U_{\infty }$ ($U_{\infty }$ the free-stream velocity) is obtained by two techniques: flow obstruction and low momentum injection. Force balance, pressure measurements and Particle Image Velocimetry are used to characterize the aerodynamics of the model while changing the underbody flow velocity. A very sharp transition in the wake is found at a critical underbody velocity $U_b=0.65U_{\infty }$. It corresponds to a sudden wake reversal with a bistable behavior between 2 equilibrium states, N or P depending on the vertical base pressure gradient or the wake orientation. The drag of the N state is larger than that of the P state. The control of the wake state by reducing the underbody flow velocity leads to beneficial increase of the base suction of approximately 20% when selecting the P state compared to the N state. The low momentum injection technique reduces drag by 10% but is ineffective at yaws 5° and 10°, while the obstruction technique consistently increases base suction but induces additional drag.

The understanding of wake recovery mechanisms is crucial for the design of efficient wind farm layouts and the development of accurate wake models. Recently, placing two vertical-axis wind turbines (VAWTs) in close proximity has demonstrated potential for increased power output. In this study, wind tunnel experiments were conducted to investigate the wake replenishment mechanisms behind paired VAWTs. The experimental campaign included testing an isolated VAWT and paired counter-rotating VAWTs. By combining qualitative observations of key flow field variables with a quantitative analysis based on momentum conservation, this study aims to enhance our understanding of the mixing mechanisms supporting the reintroduction of streamwise momentum into the wake of paired VAWTs. This research also involves a comparison of these mechanisms with those observed in the wake of a standalone VAWT. The results show that the differences between isolated and paired VAWTs in overall wake characteristics are minimal. The increased lateral advection within the wake of the isolated VAWT is offset by the enhanced vertical advection in the paired configuration, as a result of the change in the direction of cross-stream velocity within the gap between the paired VAWTs, which promotes a shift towards vertical flow rather than lateral flow.

The long jump is a track and field event in which the athlete sprints down a runway and tries to leap as far as possible from a take-off line. To the best of our knowledge, there are no published studies on the aerodynamic impact of jump style, hairstyle and clothing on the long jump distance. This paper presents a numerical-physical model of the long jump flight. It allows to predict flight distance and the impact of jump style, hairstyle and clothing. It consists of five submodels: an existing model of the sprint before take-off, a computational fluid dynamics (CFD) model of different body postures in flight, a set of physical wind tunnel models for CFD validation, a full-scale wind tunnel manikin with different hairstyles and clothing and a numerical model of the flight trajectory. Jump style only impacts flight distance by 1 cm or less. Hairstyle and clothing however can cause drag to vary by more than 25% and flight distance by more than 10 cm, mostly by impacting the take-off speed. In the long term, long jump events might see the introduction of hair caps and low-drag clothing to reduce aerodynamic resistance and level the playing field.

Vertical Axis Wind Turbines (VAWTs) have attracted considerable attention in recent years due to their potential for harvesting wind energy in urban areas and low wind speed environments. However, they suffer from inherent aerodynamic limitations such as low power coefficient and poor self-starting capabilities. To address these challenges, numerous flow control techniques have been proposed and investigated. The purpose of this review paper is to provide an overview of the various flow control techniques, including passive and active methods, that have been employed to improve the performance of Darrieus VAWTs. The concept of each flow control technique to suppress/delay separation and increase the lift-to-drag ratio is described. In addition, the effectiveness of each method is assessed based on its impact on key performance parameters. Moreover, the limitations of each technique are critically discussed and areas for further research and development are identified. Overall, this review provides valuable insights into different flow control techniques for improving Darrieus VAWTs and serves as a guide for future research in this area.

The cross-wind response generally follows an un-skewed hardening non-Gaussian distribution around vortex-resonance wind speed, a great amount of samples are required to ensure the accuracy of the peak factor. This study aims to propose a robust methodology for estimating the peak factor, even when dealing with limited samples. The accurate description of the probability distribution for cross-wind response is essential to achieve a reliable peak factor. Since both the harmonic self-excited and Gaussian buffeting components contribute to the non-Gaussianity of the cross-wind response, this study explicates the probability density function (PDF) of the composite process combining the harmonic and Gaussian elements. Subsequently, the PDF of displacement is ascertained by the energy ratio between self-excited vibration and random buffeting, also a kurtosis-based function that can be derived from limited samples. Then the cumulative distribution function (CDF) of the extreme is derived based on the displacement PDF, and a closed-form solution determined by kurtosis for peak factor is derived. Finally, the validity of the proposed method is verified through both Monte Carlo simulations and field measurements. This method offers a practical mean to estimate the extreme values of hardening non-Gaussian responses in highly flexible structures using a limited number of samples.

A series of sectional model testing were conducted to investigate the vortex-induced vibration (VIV) characteristics of parallel Π-shaped composite girders under different spacing ratios and wind attack angles. To enhance the understanding of the aerodynamic interference effects on the VIV, particular attention is devoted to the vibration amplitude, lock-in wind speed, phase difference, and spectrum characteristics of the upstream and downstream girders. Results showed that the aerodynamic interference has significant effects on the downstream girder, resulting in the VIV amplitude amplified obviously. Nevertheless, the upstream girder is less affected, with its amplitude slightly smaller or almost equivalent to that of a single-Π-shaped girder. The lock-in range and vortex shedding frequency of the upstream and downstream girders are almost unaffected by aerodynamic interference. The phase difference ϕ between the vibrations of upstream and downstream girders diminishes in a nearly linear manner as wind speed rises in the lock-in region for all spacing ratios investigated, except at the end of the lock-in region. Additionally, the initial phase difference is directly related to the spacing ratio. In addition, the fluid mechanism of VIV was analyzed by computational fluid dynamics (CFD) technique. It was found that the downstream girder experiences the alternating flow fields ' ℧ ' and ' Ω ′ generated by the upstream wake vortices, leading to VIV amplitude amplification of downstream girder.

Structural health monitoring (SHM) technology can provide useful data for the assessment of the wind-resistant capacity of a transmission tower. However, most studies on wind-induced fragility assessment are based on a significant number of simulations. In this context, a wind-induced fragility assessment framework for a transmission tower is proposed based on multi-source monitoring data and deep learning methods. The framework consists of three main steps. First, methods for processing missing data and denoising the monitoring data are developed. Subsequently, a surrogate model of structural dynamic response under wind field data input is established using long short-term memory (LSTM) networks, and the optimal model hyperparameters are obtained by Bayesian optimization. Finally, wind field data with a uniform distribution of wind speed intensities are generated, and the structural dynamic responses are supplemented by surrogate model prediction. Fragility curves are generated under a variety of wind directions. The proposed framework was validated, and its applicability and efficiency were demonstrated using monitoring data from a real transmission tower. The results indicated that wind direction has a significant influence on fragility curves. The proposed framework is capable of efficiently expanding the database of wind-induced dynamic responses and realizing more reliable and rapid fragility assessments.