Journal of Wind Engineering and Industrial Aerodynamics最新文献

Double-row flexible photovoltaic support is a new type of structure that has excellent site adaptability and cost-effectiveness. However, methods for calculating wind loads of such structures are missing in the current standards or codes. Therefore, it is essential to study the aerodynamic characteristics of double-row flexible photovoltaic (PV) panels. First, a rigid model is designed and fabricated to conduct a wind tunnel test, and the average wind pressure coefficients of the PV panels under various wind directions are obtained. Then, the wind pressure distribution characteristics on the PV panels were analysed, further revealing the unevenness of the wind pressure distribution on different panels. Additionally, the computational fluid dynamics (CFD) method was used to supplement the conditions under which wind tunnel tests cannot be carried out. The results indicate that the wind direction and inclination angle of PV panels significantly impact the wind pressure distribution. The maximum wind pressure coefficient and uneven wind pressure coefficient are −1.572 and 2.105, respectively, appearing at the top left corner of zone A with the 300° wind direction. In addition, the overall wind pressure coefficient in the leeward direction is greater than that in the windward direction. When the inclination angle exceeds 25°, the wind pressure coefficient of the PV panel fluctuates significantly, potentially resulting in adverse effects of wind on the overall structure. The research results can provide a positive reference for the wind resistance design of double-row flexible PV supports.

Synoptic extreme winds are traditionally mapped at the lower bound of the countrywide macroscale resolution (hundreds of km) on the basis of time series measured at land anemometric stations, while the assessment of the design wind speed at the construction site is entrusted to the designer within the so-called return criterion. Coarse, uneven distribution of the stations, uncertainties in their setup, measurement errors, challenging subjective evaluation of the exposure roughness, inconsistencies among national wind provisions are some of the critical issues affecting the in force map-and-return approach. This study is intended to test an alternative approach to directly assess the wind hazard at the lower bound of the meso-$\gamma$ scale resolution (about 2 km) around a construction site. The approach is grounded on data issued from a weather forecast computational model, its reanalysis by means of assimilated remote sensing observations, and possibly its downscaling. Three different reanalysis/downscaling models are adopted. The resulting wind maps over the Italian Country are critically compared with measurements at 21 stations. The errors made by each model are assessed for current and extreme wind speed with different return periods. Finally, a reanalysis-based engineering approach to design wind speed is presented by proposing model correction factors.

Wind-excited torsional oscillation of photovoltaic single-axis solar trackers constitutes a class of complex fluid-structure interaction phenomena, involving torsional galloping, torsional divergence, 1DOF flutter, VIV and buffeting. The highest potential for structural damage corresponds to torsional aero-elastic instability, which develops when wind speed exceeds a critical value that, for a given tracker, depends on tilt. Current engineering standards do not offer reliable criteria to yield safe operation conditions, therefore each case requires specific wind tunnel testing. Since data reported in the literature are scarce and scattered, from both industry and academia there is a growing need to define a Benchmark as a reference to compare results and validate methodologies of different studies. This paper proposes a tracker model with 3D aeroelastic characteristics, both torsion and bending, appropriate for wind tunnel testing, including geometry, mounting details, experimental methodology and critical velocity criterion. Tracker units built according to this model were tested in two different wind tunnels (at Polytechnic University of Madrid and University of Oviedo), and the respective measurements show good agreement. The reported results include stability maps with comparison to literature data, an evaluation of the phenomena identified, and the effects of the tracker relative position in a row.

The application of stand-alone permeable screens for the mitigation of vortex shedding problems is a well-known option in wind engineering, usually adopted for bridges. Nevertheless, their employment in buildings is still in its early stages. Porous coverings are employed for aesthetic reasons and, recently, also for their capability to reduce the energetic impact of the building. Within this framework, the Permeable Double Screen Façades (PDSFs) are becoming popular in the architectural trends, but their effects on the building’s aerodynamics are still an open topic. Specifically, it is still unclear which could be the role of the permeable layer on the vortex shedding mechanism, which currently represents one of the main design issues for tall and super tall buildings. The present study proposes an experimental investigation of the role of the PDSF in the vortex-induced vibrations (VIVs) of a prismatic building model with an aspect ratio $B/D=3.33$. A semi-aeroelastic model of the building is tested for different Scruton numbers and a comparison between the PDSF and the solid façade case is proposed. Results highlight that the effectiveness of the PDSF in structural response mitigation appears to be dependent on the Scruton number and a threshold over which the PDSF successfully mitigates the onset of VIV is found.

This experimental study investigates the performance and wake of tandem wind turbines utilising co-rotating and counter-rotating rotor configurations. Measurements for turbine power, tip-speed ratio, and wake velocity were obtained across various arrangements of single and tandem turbines. Conducted at a Reynolds number of $9.6\times 10^4$ based on turbine diameter, the study evaluates in-line configurations with separation distances from 1.25$D_T$ to 8$D_T$, $D_T$ being the turbine diameter, and different tip-speed ratios. Power measurements indicate that the downstream turbine performs better when its rotational direction opposes that of the upstream turbine, showing a 20% increase in performance compared to the co-rotating arrangement at a separation distance of $1.25D_T$. Nevertheless, the results show the tandem wind turbines’ power generation depends on the spacing between the turbines and the upstream turbine’s optimal tip-speed ratio. This indicates that as the distance between the turbines increases, the advantageous impacts of a counter-rotating setup diminish. Velocity measurements behind the downwind turbine reveal negligible effects on the streamwise velocity due to relative rotational directions but a significant impact on turbulent kinetic energy. Specifically, the co-rotating arrangement exhibits 33% higher turbulence levels than the counter-rotating arrangement. These findings hold considerable implications for designing and optimising wind turbine systems in arrays, both onshore and offshore wind farms.

In recent years, high-order vortex-induced vibrations (VIVs) of ultra-long stay cables have been frequently observed on real bridges. However, additional dampers or aerodynamic measures were often designed to suppress wind-rain induced vibrations (RWIVs) of stay cables, which is mainly for the vibrations of low-order modes. This brings new challenges to the vibration reduction of stay cables. In this study, the theoretical models are used to investigate VIV and RWIV characteristics of ultra-long stay cables and verify the validity of installing two viscous dampers at the lower end of stay cables to suppress low-order RWIV and high-order VIV simultaneously. First, an empirical model, the wake oscillator model, is introduced to study VIV characteristics of stay cables subjected to different wind profiles, damping ratio and wind velocity, and the linear wake-structure coupling resonance is also introduced to investigate VIV mechanism of the stay cable. Second, the characteristics of RWIV of ultra-long stay cables based on the existing RWIV model is investigated. Finally, the optimizing parameters of the cable-dampers system is conducted for simultaneous control of RWIV and VIV, and the multimode damping is investigated. Finally, the study compares and analyzes the control effect of the multimode vibration with different measures.

The time-dependent properties of concentration fluctuations in pollutant gas dispersion in urban areas are associated with various environmental and health assessment problems. In this study, we investigated the performance of a large-eddy simulation (LES) in predicting the time-dependent nature of pollutant gas dispersion emitted from a point source near the ground in a realistic urban area representing a highly dense city in Tokyo. A wind tunnel experiment was conducted on the gas dispersion using a fast flame ionization detector for numerical validation. We found that the LES results were qualitatively in good agreement with the experimental results for the mean concentration and higher-order moments. The vertical distributions of the concentration statistics above the main road where the mean plume path from the source was located were similar to those of the open terrain, although there was an approximately vertically constant distribution in the wake region of the high-rise buildings. The LES accuracy was quantitatively evaluated using validation metrics for the concentration statistics. A slightly poorer agreement for higher-order moments was observed despite obtaining good results for the mean concentration.

Although the important role of turbulence intensity (Ti) in wind-induced effects on many civil structures have long been acknowledged, there is a lack of concerns with the Ti influence on high-rise buildings at coastal areas especially under typhoon dominated conditions. Existing results suggest that typhoon wind turbulence may differ from that of conventional wind (e.g., strong monsoon), owing to the existence of complex small-scale eddies/vortexes. Meanwhile, due to the effects of air-sea interaction, marine roughness tends to vary with the strength of upwind wind, and the onshore wind at coastal areas may not be modeled via a single type, e.g., following the way as stipulated in many wind load codes/standards. To this end, this article investigates the Ti-dependence of wind effects toward a super-tall building with curved cross section at a typhoon-prone coastal area, based on combined usage of wind tunnel tests and field measurements. The dependence of Strouhal number, wind pressure, layer force, structural response and equivalent static wind load on Ti in the range from 2.5% to 31.0% is analyzed and further compared with those for circular and square cylinders. The results show that Ti has a significant impact on the wind-induced effects on structures. As Ti increases, the mean and fluctuating pressures on wind structure surfaces keep rising. The frequency of vortex shedding increases with Ti by changing the vortex generation state at shear layer in the wake region. In addition, the global geometric characteristics of cross-section and its local details, especially the location of blunt edges which might lead to flow separation, may play an important role in the effect of Ti on fluid structures around the building. These factors above collectively result in significantly growing fluctuating values of wind loads on the structure as Ti increases. Overall, the structural response of this building gradually increases with the enhance of Ti, although the mean value of layer load may decrease with that.

Aerodynamic drag in sports can be assessed using a multitude of methods such as wind tunnel tests, computational fluid dynamics simulations or field tests. All these methods are able to simulate specific situations in sports. The goal of this study was to describe a measurement system that assesses the aerodynamic properties of textile covered cylinders in a special situation: contrary to wind tunnel measurements, fabric-covered samples were moved in stationary air over a distance of up to 20 m at speeds from 5 to 20 ms⁻¹. The measurement system showed a precision better than 2%. The course of the drag coefficient over speed was very similar to comparison measurements in a wind tunnel, but the drag coefficient was lower by up to 18% with respect to the wind tunnel and the speed at which the drag crisis occurred in the wind tunnel was higher by up to 10 ms⁻¹. Reasons could be a higher turbulence intensity in our measurement setup or, more likely, that the motion of the sample was too short to build up a steady air flow as in wind tunnels. The limited duration of the experiment, however, maybe brings it closer to the reality in situations in sports where the athlete's posture and/or direction of motion change frequently or for some aspects of sports ball aerodynamics.

Large eddy simulations (LES) of “tornado-like” vortices (TLVs) for a range of swirl ratios and surface roughness were conducted. The mean axial velocity distribution was used to identify a region of predominantly horizontal flow. An examination of the boundary layer within this inflow region was conducted with the primary objective of applying the traditional understanding of atmospheric boundary layer (ABL) to TLV boundary layer. A comparison with the boundary layer development over a flat plate revealed that the tornado boundary layer can be divided into a region of zero and favourable pressure gradient. Furthermore, the mean measures of the boundary layer in TLVs like the BL depth, displacement thickness, and momentum thickness were observed to be dependent on the external swirl ratio, ground roughness, and streamwise distance. The turbulent stresses, friction velocity and the aerodynamic roughness length in the TLV boundary layer were also observed to depend on the streamwise distance, indicating a lack of equilibrium due to a short fetch. ESDU predicted turbulence intensities, based on a crude comparison, were observed to be conservative for the lateral and vertical directions but under-conservative for the longitudinal component in regions marked by high aerodynamic roughness length.