Wind Pressure Coefficients Research Articles

Effects of wind barriers on the aerodynamic characteristics of twin-separated parallel decks for a long-span rail-cum-road bridge

The aerodynamic characteristics of twin-separated parallel decks for long-span rail-cum-road bridges with various wind barriers clamped at railway girder are more complicated because of aerodynamic interference. Experimental investigations on aerodynamic coefficient and wind pressure coefficients of twin girders under different incoming flow directions were conducted using wind tunnel tests. Three different heights ( H) varying from 2 m to 4 m and four different ventilation ratios ( R) varying from 20% to 50% for wind barriers were examined. Results indicated that the aerodynamic coefficients were affected significantly by the incoming wind direction, which must be considered, and the railway wind barrier affected the aerodynamic characteristics of the railway girder when it is located both upstream and downstream, but the laws are not the same. Due to the aerodynamic interference effect of the twin parallel girders, the aerodynamic characteristics of the adjacent highway girders were also affected by the wind barrier along the railway girder, especially when the highway girders were located downstream. While, the highway girders were less affected when located upstream. The influence of wind barrier height and ventilation ratios on the adjacent highway girders was completely different. Most importantly, the parameters optimization of wind barriers clamped at railway girders should be determined after a comprehensive evaluation of the aerodynamic characteristic of both the railway and highway girders.

Effect of void space arrangement on wind power potential and pressure coefficient distributions for high-rise void buildings

High-rise void building complexes can augment the permeation of airflows over buildings, and thereby strengthen urban wind energy harvesting for realization of the sustainable development goals (SDGs). This paper considers the wind over a typical 2×2 compact high-rise building array with the openings to analyze the wind power potential at varying void sizes, locations of voids, and direction of incoming wind. The predicted mean wind speeds and turbulence intensities are compared against the measured data with 4 generic high-rise building models having voids in an atmospheric boundary layer wind tunnel for validation of the computational model. Based on the comparative results from four common Reynolds-averaged Navier-Stokes (RANS) turbulence models including the standard, realizable, renormalization group (RNG) k-ε, and shear-stress transport (SST) k-ω models as well as the Reynolds stress model (RSM), the RSM approach can provide the most accurate predictions of streamwise mean velocity and turbulence intensity. The present study then conducts CFD simulations to explore the effects of opening configuration and wind direction on the wind field around high-rise void buildings. Considering the variations of void sizes of 10 × 10 m2, 12.5 × 12.5 m2, 15 × 15 m2, void heights of z/H = 0.25, 0.5, 0.75 and wind directions of 0°, 45°, respectively, the simulated results indicate elevated wind power densities with acceptable turbulence intensities over the upstream gap passage and void channels to achieve prospective urban wind power harvest and mitigate wind load on structures of high-rise void buildings.

Aerodynamic characteristics of a streamlined box girder under shear flow considering oncoming turbulence

Non-synoptic winds, such as typhoons and downbursts, are frequently characterized by shear flow associated with turbulence, which affects the aerodynamic performance of long-span bridges. To reveal the aerodynamic characteristics of streamlined box girders under non-synoptic winds, multi-fan wind tunnel (MFWT) tests were used to investigate the aerodynamic effect around a streamlined box girder considering the action of shear flow with different velocity gradients, turbulence intensities, and integral scales. In the MFWT tests, the high shear rate and large turbulence intensity were observed to magnify the mean wind pressure coefficient, whereas the variation in the turbulence integral scale had a slight effect on the mean wind pressure coefficient distribution. An increase in the shear rate was observed to be beneficial in reducing the drag and moment coefficients, as well as in increasing the lift coefficient. The empirical aerodynamic prediction relationships revealed that the influence of turbulence intensity on the aerodynamic coefficient is non-linear, whereas that of the turbulence integral scale and shear rate on the aerodynamic coefficient is linear. Additionally, the large eddy simulation (LES) method was used to study the vortex-shedding behaviors and aerodynamic spectrum characteristics of the streamlined box girder under shear flow. The LES results showed that larger shear parameters amplify the amplitudes of high-frequency aerodynamic forces. The vortex frequently begins from the low-velocity side of the streamlined box girder, which induces a suction effect on the low-velocity side that is greater than that on the high-velocity side.

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.

The Dependence of the Location and Pressure Variations of the Martian Magnetic Pileup Boundary on the Interplanetary Magnetic Field: An MHD Simulation Study

Abstract In this paper, using a three-dimensional multispecies MHD model, we study the effect of the interplanetary magnetic field (IMF) intensity and orientation on the subsolar standoff distance of the Martian magnetic pileup boundary (r 0) and the pressure balance across it. The results show that: (1) with the increasing magnitude of the Y- or Z-component of the IMF, B Y or B Z , r 0 increases, while the radial IMF component, B X , has little effect. With the increasing magnitude of B Y or B Z , the compression degree of the magnetic field (f) increases, while the solar wind pressure coefficient (k) remains unchanged, resulting in the enhancement of r 0. (2) Under the same IMF intensity, B t , the impact of the IMF cone angle on r 0 and f is controlled by the ratio of the IMF Y- and Z-components to B t , B Y 2 + B Z 2 / B t . When the ratio is enhanced, both r 0 and f increase, while k generally remains unchanged. Compared with the IMF cone angle, the influence of the IMF clock angle is relatively less. We suggest that the stronger magnetic pileup process controlled by the perpendicular IMFs (B Y or B Z ) causes the larger r 0, while the weaker magnetic pileup under the radial IMF leads to the smaller r 0. The difference in the IMF effect on the size of the Martian magnetic pileup boundary and the terrestrial magnetopause reveals different solar wind interactions with a magnetized and unmagnetized planet. Last, the location of the intense crustal field can also affect r 0 and the pressure balance condition, and the specific impact needs to be further studied.

Numerical and Experimental Study on Flow Field around Slab-Type High-Rise Residential Buildings

High-rise residential buildings often adopt rectangular cross-sections with large depth-to-width ratios. Moreover, the cross-sections have many grooves and chamfers for better ventilation and lighting. However, related research is lacking. This study performed wind tunnel tests and large eddy simulations (LES) on two typical buildings to analyze the surface wind pressures and flow fields around the buildings. The base moment spectra, along with the wind pressure coefficients, demonstrate that numerical simulation is capable of accurately representing the magnitudes and variations in wind loads along the height of the building. Furthermore, numerical simulation effectively captures the dominant energy distribution characteristics of fluctuating wind loads in the frequency domain. The shear layer separations, vortex shedding and reattachment phenomenon were observed. It was found that in the middle and lower parts of the buildings, the shear layer separation changed dramatically. Buildings with depth-to-width ratios close to 2 are minimally affected by changes in wind direction. However, for buildings with larger depth-to-width ratios, especially when the short side faces the wind, the reattachment of the shear layer and the shedding of wake vortices become crucial factors in generating fluctuating cross-wind loads. This emphasizes the significant impact of wind direction and plan dimensions on flow characteristics and aerodynamic behavior. When the building contained corners and grooves, the low-wind-speed area induced by the shear layer separation shrank and the reattachment point shifted closer to the windward facade.

Aerodynamic loads of tapered tall buildings: Insights from wind tunnel test and CFD

Tapered modifications have been widely utilized for tall buildings to reduce their wind effects in practical engineering. However, the flow mechanisms caused by tapering and relevant empirical models for wind loads estimations of tapered tall buildings are still unknown. In this study, both wind tunnel test and CFD were used to study the aerodynamic performance of tapered tall buildings. Taken the CAARC standard tall building model as the benchmark model, another four modified models with taper ratio of 0.05, 0.10, 0.15 and 0.20 were designed and tested by pressure measurements and large eddy simulation (LES). The variations of wind pressure coefficients, local wind force coefficients, base moment coefficients, wind load power spectrum and vertical coherence function of five models with different taper ratios were discussed and compared. Also, the streamline of mean and fluctuating velocity around tapered tall building models are provided for better understanding of the flow mechanisms. The results showed that aerodynamic performance of the tapered tall buildings has been improved effectively, especial for across-wind effects. This study aims to provide reference for aerodynamic optimization design of tapered tall buildings.

Reliability assessment and performance improvement of long-span roof structure subjected to coupled wind-snow multi-hazard

Sensitivity to wind and snow loads has been the focus of reliability analysis and safety design of long-span roof structures in cold regions. In this study, the reliability assessment and performance improvement of a long-span roof structure subjected to coupled wind-snow multi-hazard are addressed. To this end, the average wind pressure coefficients of roof surface are first derived from wind tunnel tests, and the two-dimensional wind velocity field simulation is carried out by using the refined spectral representation scheme based on joint wavenumber-frequency power spectrum and stochastic harmonic function. The snow pressure coefficients of structural roof considering wind-induced snow drift effects are obtained by conducting computational fluid dynamics simulation. Then the global reliability of the structure subjected to coupled wind-snow multi-hazard with 100-yr return period is assessed using the probability density evolution method (PDEM). To improve structural performance, a control scheme of distributed tuned mass dampers (d-TMDs) is designed according to the structural dynamics of their deployment positions. Numerical results show that the fluctuating wind is a critical factor resulting in deformation failure of the long-span roof structure, and the proposed control scheme has sound effectiveness and robustness to mitigate the fluctuating wind effect and thus improve the structural performance.

Wind tunnel experiment of wind-induced single-sided ventilation under generic sheltered urban area

Natural ventilation is an important ventilation method due to its potential to improve indoor air quality and provide an acceptable thermal environment without energy consumption. In the urban area, the ventilation performance of the natural ventilation is very sensitive to surrounding building density. This paper presents a wind tunnel experiment to assess the influence of urban density on the ventilation rate of single-sided ventilation. Spacing density, wind direction, and the number of openings were factors that were investigated in this experiment. The ventilation rate is evaluated by a continuous dose method of the tracer gas technique. The wind pressure coefficient at openings of the sealed model without openings was measured by pressure transducers. The streamwise velocity at the street canyon was measured by a split-film probe with a constant temperature anemometer unit. The ventilation rate, wind pressure coefficient fluctuations and velocity of an isolated building are compared to those of a building with two layers of surrounding buildings with the spacing of 0.5H (H is building height), 1H and 1.5H. A higher building density decreases the ventilation performance of windward opening cases and increases the ventilation performance of the leeward opening cases. The simplified ventilation rate prediction methods for wind-induced ventilation are presented.

Aerodynamic stability and vibration mechanism of long-span flat roofs with various span to eaves-height ratios

Computational fluid dynamics (CFD) based on large eddy simulation (LES) is used to investigate the aerodynamic stability of long-span flat roofs with various span/eaves-height ratios (L/H) in this study. Forced vibration tests, where vibrations are induced in the first antisymmetric mode with various frequencies, are conducted on vibrating as well as rigid roofs with L/H = 3, 6, and 9 to obtain distributions of the wind pressure coefficients. The primary focus is the effect of L/H and that of the approach flow turbulence on the aerodynamic stability of the roof, which is quantified using energy consumption. The work done by the unsteady aerodynamic forces on the vibrating roof during the period of vibration was computed using the time histories of the wind pressures at various points on the roof. Furthermore, fluctuating wind pressures and energy consumption are characterized using complex proper orthogonal decomposition (CPOD) analysis. Finally, the vibration mechanism is discussed based on the energy consumption and convection of the wind pressures obtained from CPOD analysis. The results indicate that smooth flow has a higher probability of inducing aerodynamically unstable vibration than turbulent flow because of the phase excitation.

Numerical Investigations of Wind Impacts on Chinese Ancient Architectural Roof Surfaces with Ridges and Semi-Cylindrical Tiles

ABSTRACT This study aims to evaluate the impacts of roof ridges and semi-cylindrical tiles on the wind loading on traditional single-eave hip roofs. To the best of the authors’ knowledge, the semi-cylindrical tiles have been considered in the simulation of ancient Chinese architecture for the first time. Several roof models with various ridges and semi-cylindrical tiles are simulated by solving the Reynolds-averaged Navier-Stokes equations (RANS) using the computational fluid dynamics (CFD) technique. The results reveal that the addition of roof ridges and semi-cylindrical tiles has a considerable structural protection effect, which can significantly reduce the suctions, as well as the turbulence fluctuation, on both the windward and leeward sides: the average of negative mean wind pressure coefficients is reduced by 33% on the leeward surface, and approximately 48% on the windward surface one. When the number of protruding ridges and semi-cylindrical tiles increases (decreasing the diameter of them by 40%), the average of area mean wind pressure coefficient for all the wind directions decreases by about 30% on the windward side and about 50% on the leeward side. The average of maximum spatial wind pressure coefficient decreases by about 25% on the windward side and about 40% on the leeward side.

Evaluation of a Measurement Turbulence Model of the Wind Pressure on the Ruin of a Fortified Tower

Abstract An analysis of the external pressure coefficient on the surface of a ruin in different flow directions is presented. The ruin has almost cube-like proportions with an open roof plane and a destroyed corner. Flow simulations were performed using 3D Time Steady RANS and compared with experimental results from the boundary layer wind tunnel at the Slovak University of Technology in Bratislava. The optimal turbulence model and internal mesh settings were selected based on their statistical evaluation. For an evaluation of the critical directions of the wind flow around the ruin, the values of the external wind pressure coefficient were obtained from the selected calculation model and settings.

Wind tunnel test study on the wind load variation law of a point focus solar furnace

This work studied the wind load acting on a point focus solar furnace composed of a 110 m2 heliostat and a 77 m2 concentrator through wind tunnel testing. Based on wind tunnel test data under 305 different working conditions, the variation laws of the wind pressure coefficient, power spectral density, and wind load coefficient of the heliostat and concentrator were analyzed. The results showed that due to the interaction between the concentrator and heliostat, the wind speed near the heliostat and concentrator decreased but the turbulence intensity increased, which caused the peak wind load coefficient to rise slightly. The results suggested that a safety factor of 1.1–1.2 should be considered for structural design and optimization of solar furnaces.

Prediction of Wind-Pressure Coefficients on Circular Elevated-Tanks Through the Novel CFD-ANN Model for Various Building-Interference Circumstances

ABSTRACT The authors have studied the wind-shielding effect on circular elevated tanks with computational fluid dynamics (CFD) analyses, caused by rectangular plan-shaped buildings, which alter wind load significantly. Velocity- streamlines have been observed to understand the effect of wind flow on the pressure due to building interference. The present CFD model has been validated with experimental literature. Supervised learning is done for different percentages of CFD data (33%, 55%, 66% and 88%) using various artificial neural network (ANN) architectures, among which the performances of three combinations (one, two and three hidden layers) are provided. Input variables are spacing between structures, interference height, wind angle and peripheral angle. Output parameters are time-average and fluctuating coefficients of wind pressure, distributed circumferentially around tankwall. Data ≥55% are sufficient for precise ANN training. The proposed ANN model efficiently predicts mean and fluctuating circumferential wind pressure coefficients on tank-wall for building-interference, in very little time, with 98.15% and 98.43% accuracy, respectively, benefitting structural designers.

An enhanced k-[formula omitted] SST model to predict airflows around isolated and urban buildings

The goal of this research is to improve and validate a Reynolds Averaged Navier–Stokes (RANS) turbulence model to perform accurate Computational Fluid Dynamics (CFD) simulations of the urban wind flow. The k-ω SST model is selected for calibration since its blended formulation holds remarkable optimization potential and has increased relevancy in recent studies in the field. A simulation-based optimization approach recalibrates the model closure constants by minimizing the prediction error of wind pressure coefficients on an isolated cubical building because this scenario contains many salient features observed in the flow in actual urban areas. The optimization procedure ensures both the coherence of calibrated model constants involved in the wall function formulations and the relationship between them to satisfy the flow horizontal homogeneity of the atmospheric boundary layer. The tuned closure coefficients increase momentum diffusion in the wake, resulting in shorter and more accurate predictions of the reattachment lengths. Validation case studies with wind tunnel measurement data from various urban scenarios were addressed to comprehensively assess the adaptability of the optimal set of coefficients reached. The results confirm that CFD predictions with the optimized model are consistently in closer agreement with experimental data than the standard version of k-ω SST. The root mean square errors are reduced by about 75% in pressure, 40% in velocity, and 20% in turbulent kinetic energy.

Wind effect on scallop domes with negative amplitude and prominence using Experimental and Numerical Study

This study investigates the wind effect on hexa-sectored scallop domes using Computational Fluid Dynamics (CFD) and wind tunnel tests. Similar to the shape of a seashell, the scallop dome is one of the most common domes used to cover large spans. The scallop dome has an additional curvature equal to its sectors compared to a base dome (spherical). Hence, it has better structural efficiency compared to a spherical dome under the same condition. The curvatures on the scallop dome create alternate “ridges” and “grooves” on it. According to the computations of the article, the grooves created on this dome in the sector, as well as their position angle to the wind direction significantly affect pressure coefficient value. Due to these differences, wind pressure on scallop domes significantly differs from wind pressure on spherical domes. The results indicate that the ridges cause negative wind pressure coefficients whose magnitude reaches a maximum of −2.0 for an angle of alignment of 30°. The analyses have been conducted through Ansys-Fluent. This study presents the equation of wind pressure coefficient in the most critical of dome groove positions. The arch created between the grooves of a scallop dome is another effective parameter on maximum negative pressure. In the case study scallop dome, if the wind effect angle is considered α = 15, the maximum deformation in the structure will be created, which is 20% higher than that of α = 0.

Large-span M-shaped greenhouse with superior wind resistance and ventilation performance

In order to reduce wind-caused disasters and reduce the cost of production in summer, the large-span M-shaped greenhouse with superior wind resistance and cooling performance is proposed. This paper carries out a research on the optimization with the V-angle of M-shaped greenhouse, and the wind effect and ventilation performance of the optimized M-shaped greenhouse and ordinary large-span arch greenhouse (ordinary arch greenhouse) are studied and comparatively analyzed. It is obtained that the wind resistance of M-shaped greenhouse is optimal at a V-angle of 95°. For the four cases of relatively large net wind pressure coefficients of opening windward side vent, leeward side vent, side vents and top vents, the maximum net wind pressure coefficients of M-shaped greenhouse are lower than those of ordinary arch greenhouse. M-shaped greenhouse has higher ventilation efficiency and slightly lower temperature than ordinary arch greenhouse. It can be seen that M-shaped greenhouse has excellent wind resistance in both closed and open states, and has good ventilation and cooling effect in summer. It can be widely used in agricultural production as new wind-resistant cooling plastic greenhouses.

The study of wind-interference effect on an elevated RC circular tank due to an adjacent building

Elevated water tanks are constructed to store and supply the water to a building (residential, official, commercial, institutional, etc.) or community, as per demand. Elevated tanks are vulnerable under wind loading, especially when empty. Due to the unavailability of proper and adequate literature on the effect of wind loading on reinforced concrete (RC) circular elevated tank, the present authors have taken up this issue for study. The effect of interference of wind on an elevated RC water tank with circular cross-section, caused by a building adjacent to that water tank, has been studied by performing fluid structure interaction (FSI) analyses. The along and across wind flow cases have been considered to understand the effect of wind directionality. The spacing between the elevated tank and the building, along with the height of interfering building have been varied. The wind pressure coefficient distribution and the deformation contour of the empty elevated tank for isolated and building-interference conditions have been calculated and compared. The concentration of wind-pressure (which is positive in nature) at windward region of principal elevated tank decreases with the decrease in proximity between the tank and the interfering building, for along wind flow condition. Due to the proximity of the interfering building, high deformation zone has been observed at the side region of the elevated principal tank, under the excitation of along wind flow. Also, the magnitude of the deformation of the elevated tank decreases with the decrease in the proximity of the interfering building from the tank, considering the along wind flow. In case of across wind flow, the high deformation zone can be observed at the windward region of the elevated principal tank. The elevated tank columns are observed to exhibit sway under the transverse effect of wind loading.

Physics-informed few-shot learning for wind pressure prediction of low-rise buildings

This research proposes a physics-informed few-shot learning model to predict the wind pressures on full-scale specimens based on scaled wind tunnel experiments. Existing machine learning approaches in the wind engineering domain are incapable of accurately extrapolating the prediction from scaled data to full-scale data. The model presented in this research, on the other hand, is capable of extrapolating prediction from large-scale or small-scale models to full-scale measurements. The proposed ML model combines a few-shot learning model with the existing physical knowledges in the design standards related to the zonal information. This physical information helps in clustering the few-shot learning model and improves prediction performance. Using the proposed techniques, the scaling issue observed in wind tunnel tests can be partially resolved. A low mean-squared error, mean absolute error, and a high coefficient of determination were observed when predicting the mean and standard deviation wind pressure coefficients of the full-scale dataset. In addition, the benefit of incorporating physical knowledge is verified by comparing the results with a baseline few-shot learning model. This method is the first of its type as it is the first time to extrapolate in wind performance prediction by combining prior physical knowledge with a few-shot learning model in the field of wind engineering. With the benefit of the few-shot learning model, only a low-resolution of the measuring tap configuration is required, and the reliance on physical wind tunnel experiments can be reduced. The physics-informed few-shot learning model is an efficient, robust, and accurate alternate solution to predicting wind pressures on full-scale structures based on various modeled scale experiments.

Experimental study on fluctuating aerodynamic force and wind pressure distribution characteristics of three circular cylinders arranged inline

The fluctuating aerodynamic force and wind pressure distribution characteristics of three equally spaced circular cylinders arranged inline at different incidence angles and spacing ratios were studied via rigid model pressure measurement wind tunnel tests. The results were compared with those of a single cylinder. The Reynolds number is 6.4 × 104. The range of incidence angle α and spacing ratio L/D (the ratio of the center distance between adjacent cylinders to the diameter of the cylinder) are 0°∼90° and 1.2 ∼ 4.0, respectively. The spacing ratio and incidence angle greatly influence the fluctuating aerodynamic force coefficients and wind pressure coefficients. According to the spacing ratio, the fluctuating aerodynamic characteristics can be roughly divided into three states: small spacing ratios (1.2 ≤ L/D ≤ 2.0), medium spacing ratios (2.0 < L/D < 3.5), and large spacing ratios (3.5 ≤ L/D ≤ 4.0). The interference effect in the fluctuating aerodynamic force and wind pressure coefficients in the three states is discussed. At small spacing ratios, the fluctuating aerodynamic force and wind pressure coefficients mainly experience a significant reduction effect. At medium and large spacing ratios, the interference effect is closely related to the incidence angle and spacing ratio.