Mean Pressure Coefficients Research Articles

Aerodynamic characteristics of tall building with wind turbines at corners

This study experimentally investigates the impact of a pair of vertical-axis wind turbines at the leading corners of a tall building on its aerodynamic characteristics. These wind turbines have the potential to serve dual purposes: harnessing wind energy under normal wind conditions and mitigating wind loading of the building under strong wind conditions. The wind tunnel testing results in this study indicate when the tip speed ratio of the turbines is 0.34, with the wind turbines rotating toward downstream, the standard deviation of lift coefficient of the building decreases by 30.9%. Meanwhile, the mean pressure coefficient and the standard deviation of pressure coefficient on both the side face and leeward face of the building also exhibit a certain degree of reduction. The peak value of the power spectral density of lift coefficient of the building is also significantly decreased. This study clearly demonstrates that the wind turbines at the leading corners of tall buildings have the potential to effectively reduce wind loading of the buildings.

Characterization of tornado-induced wind pressures on a multi-span light steel industrial building

This study presents the characteristics of external wind pressures of a multi-span light steel industrial building through wind pressure measurements conducted in a tornado simulator. The test model is designed as a three-span low-rise building with gable roofs according to the practical measured sizes and shapes of the light steel industrial building destroyed in the Shengze tornado, China (2021). The distance from the tornado-like vortex center to the building, building orientation, roof angle, and swirl ratio are considered as experimental parameters. The effects of the parameters on the most unfavorable peak and mean pressure coefficients of each surface are analyzed. The roof zoning specified in ASCE 7–16 was re-analyzed based on the characteristics of wind pressure coefficients, and the tornado design pressure coefficients were calculated. The results of the analysis illustrate that the wind-ward roof surface at a distance of around one vortex core radius from the center experience the most severe pressure coefficient under tornado, the most unfavorable zone of the pressure coefficients on the building roof changes with the building orientation, the model with a smaller roof angle has smoother pressure coefficient contours than that with a larger roof angle because of the cutting effect of the ridge, and the simulated tornado with the lower swirl ratio generate higher external pressure coefficients on the building model. Moreover, the roof zoning in ASCE 7–16 for the boundary layer wind is not precise for tornado, thus an updated roof zoning for the tornado design pressure coefficients is defined.

Interference effect on super large twin cooling towers exposed to stationary tornado-like vortices

A comprehensive investigation was conducted aiming at the interference effects on wind pressure distribution, aerodynamics characteristics, structural stability and reinforcement areas of super large twin cooling towers exposed to tornado-like vortices, and the effects of swirl ratios of tornados, grouped tower layouts, and relative central distances between the towers and the tornado were analysed based on a tornado-like vortex simulator. Two types of rigid model wind tunnel experiments were constructed for base forces and wind pressure distribution measurements. The experimental results demonstrate that the interference effects on base forces and local wind pressures are significantly influenced by the swirl ratios, central distances, and grouped tower layouts, etc. Moreover, the layout with a tornado located on the side of tandem twin cooling towers (along with the tornado translation direction being perpendicular to the central axis of the tandem combined twin cooling towers) is the most unfavourable, resulting in obvious amplification effects on base forces and local wind pressures compared with an isolated tower, and the maximum of interference factors (IFs) is 1.68 and 1.41 for the along-wind total wind force coefficient and minimal net mean pressure coefficient respectively. Subsequently, local stability indices and time-variant dynamic reinforcement envelopes were selected as the other evaluation criteria for estimating the interference effects on the cooling towers exposed to the tornado-like vortices, and the interference effects result in enlargements of the structural responses with the maximal IF of 1.36 for the inside meridional reinforcement. Finally, the various interference criteria at aerodynamic loading and structural reinforcement aspects were contrastive analysed, showing that the criterion of time-variant dynamic reinforcement area envelopes is a more reasonable criterion for evaluating the interference effects on the super large cooling towers exposed to the tornado-like vortices. This investigation aims to contribute to a better understanding of the wind-related effects of the cooling towers exposed to extreme non-synoptic winds, particularly tornadic vortex impacts.

Wind-induced interference effect of complex building clusters on long-span roof structures

The presence of complex buildings introduces interference effects and complicates the wind field around the long-span roof structure. The complexity of the problem makes it challenging to predict wind load of long-span roof structures, resulting in a scarcity of design data available to engineers and designers. Thus, the influence of interference effect on mean and peak pressure coefficients of a long-span tri-centered cylindrical roof structure was investigated through wind tunnel tests conducted in an atmospheric boundary layer wind tunnel. The study focused on the interference effects caused by two cooling towers, chimney, and some low-rise buildings, considering all wind directions. The results show that the interference effects are the result of a combination of amplification effects from the adjacent cooling towers and chimney and shielding effects from the surrounding low-rise buildings. Due to the shielding effect of low-rise buildings, the wind suction on the roof is mitigated compared to that of a single building, while at the end of the roof, wind suction is amplified by cooling tower effects. The interference effect of the building clusters, however, amplifies the fluctuating wind pressure coefficient and the peak pressure coefficient on the roof. To accurately estimate the wind load of building components and envelopes, furthermore, this study investigates the influence mechanism of interference effect on non-Gaussian characteristics of wind pressure combining with fluctuating wind pressure spectrum, spatial correlation of fluctuating wind pressure, and probability distribution characteristics of standardized wind pressure coefficient. The spatial correlation of wind pressure in the roof interference area exhibits a strong association, and the probability density distribution characteristics of the standardized wind pressure coefficient significantly deviate from the Gaussian curve, with a peak factor exceeding 3.5. Thus, it can be concluded that the wind pressure within this region demonstrates significant non-Gaussian characteristics. Hence, the zone values of peak pressure coefficients are determined using the peak factor approach to inform the wind resistance design of the envelope structure.

Convolutional neural network-based wind pressure prediction on low-rise buildings

A new model of wind pressure prediction for low-rise buildings is built based on deep convolutional neural network (CNN), and the model is trained and tested by the aerodynamic data from international open database. The prediction accuracy is compared with that of the literature, and then comprehensive error analysis on all 335 predicted taps under 3 untrained wind directions are carried out for mean and RMS pressure coefficients by various error metrics. The study shows that the distributions of mean and RMS coefficients predicted by the CNN model are closer to the experimental results in comparison with those predicted by the traditional artificial neural network (ANN) model and the common deep neural network (DNN) model without the convolution and pooling layers. The relative error on the corner tap is 13.5%, 4.3% and 0.1% by the ANN, DNN, and CNN models respectively. The mean-square-error (MSE) of the corner bay and the whole roof are also eminently reduced by the CNN model. By introducing the convolutional and pooling layers, more prediction errors are confined within 5% and basically no errors exceed 20%. Consequently, the CNN algorithm can be applied in solving various wind pressure prediction problems on buildings in the future work.

Experimental and numerical study on the local crosswind environment of a wide streamlined bridge deck equipped with wind barriers at different angles of attack

In this study, the effects of wind barriers on the crosswind environment of vehicle safety on a long-span bridge with a streamlined bridge deck were investigated at different angles of attack (AOA). The profiles of the mean and the root mean square (RMS) of the wind pressure coefficients above different traffic lanes were obtained through synchronous pressure measurements. The mean pressure fields around the bridge decks were investigated by computational fluid dynamics (CFD) simulations. The crosswind environment of vehicle safety between the deck with railings and the deck with wind barriers was compared and analyzed in detail at different AOA. The results showed that the wind barriers produce a thicker separation shear layer above the bridge deck and result in a larger negative pressure region in comparison with the case with railings. This leads to a notable reduction in the mean wind pressure coefficients above the deck. The increase in the AOA enhances the above-mentioned reduction effect. It was also found that the wind barriers significantly increase the RMS of the wind pressure coefficients above the deck compared with the railings. The increase in the AOA inhibits this enhancement effect. The results of the equivalent mean pressure coefficients show that the wind barriers reduce the vehicle sideslipping risk more effectively than the vehicle overturning risk. It was also found that the effect of the wind barriers on the reduction of the overturning risk is more sensitive to the change in AOA than the effect on the reduction of the vehicle sideslipping risk.

Experimental study on wind load characteristics of rooftop canopies of low and medium rise buildings

Rooftop canopy is popular in buildings, and it is prone to wind induced damage due to its light weight and slender configuration. However, investigation on the wind load on this kind of structure has not been conducted, leading to a wind resistant design without a firm basis. This study measures the wind pressure acting on the rooftop canopy considering 4 different underneath building heights, whose prototype vary from 6m to 24m. The mean, fluctuating, and extreme wind pressure coefficients are examined. The correlation coefficients between the pressures at different positions are also checked. Results show that the underneath building height has significant effect on the wind load coefficients of the canopy. The correlation between wind pressures on both the upper and lower surfaces decreases gradually with the increase of the building height. The most unfavorable height of building found in this study is 12m, with the largest uplift net pressure coefficient of the canopy close to −7.0. Comparison with the design values for claddings of free roof in ASCE 7–22 shows that the rooftop canopy can practically have much larger uplift (negative) net pressure in the edge region.

Numerical study on influence of surface vegetation on aerodynamics of high-rise buildings

Vegetation on the surface of buildings is becoming popular in modern society. Besides their environmental and visual effect, vegetation can also affect the flow around them. In this study, the impact of surface planted trees on the aerodynamics of high-rise buildings under atmospheric boundary flow is investigated. Large eddy simulation is employed for the quantitative study. The results indicate that fluctuating lift force of building with both continuous ribs and fully planted trees can be 15.3% lower than that with ribs only. A closer examination on the model's surface pressure indicates that trees primarily decrease the mean and fluctuating wind pressures on the model's sidewalls by up to 20% and 26%, respectively. The mean flow field shows the separation bubble of the models with trees are significantly compressed and pushed away from the side face. Such flow structure contributes to the reduction of mean pressure coefficient at the vortex core of the separation bubble and side faces comparing to the reference model. Additionally, results also show that trees can significantly reduce flow fluctuations near the side faces of model, which is responsible of reduction of the fluctuating wind pressure coefficients on the model surfaces.

Toward the Usage of Deep Learning Surrogate Models in Ground Vehicle Aerodynamics

This study introduces a deep learning surrogate model designed to predict the evolution of the mean pressure coefficient on the back face of a Windsor body across a range of yaw angles from 2.5∘ to 10∘. Utilizing a variational autoencoder (VAE), the model effectively compresses snapshots of back pressure taken at yaw angles of 2.5∘, 5∘, and 10∘ into two latent vectors. These snapshots are derived from wall-modeled large eddy simulations (WMLESs) conducted at a Reynolds number of ReL=2.9×106. The frequencies that dominate the latent vectors correspond closely with those observed in both the drag’s temporal evolution and the dynamic mode decomposition. The projection of the mean pressure coefficient to the latent space yields an increasing linear evolution of the two latent variables with the yaw angle. The mean pressure coefficient distribution at a yaw angle of 7.5∘ is predicted with a mean error of e¯=3.13% when compared to the WMLESs results after obtaining the values of the latent space with linear interpolation.

Wind induced peak pressures on low-rise building roofs via dynamic terrain computational methodology

Computational Wind Engineering is expanding rapidly in the last decade and is expected to be introduced as a design tool for wind-induced loads in future code provisions and standards worldwide. The paper discusses the current CWE shortcomings of the state-of-the-art and proposes a methodology that targets to close the current research gaps, from a practical point of view. Monitoring wind tunnel experiments, significant deviations of instantaneous velocity profiles due to high turbulence intensity are expected to be critical for design pressures. This inspired the novel modeling technique - named Dynamic Terrain - that reformulates the turbulence characteristics and assumes that each instantaneous profile is produced by changing the corresponding terrain conditions. Successively derived profiles from the wind tunnel are introduced as inlet conditions in coarse LES computational domain and propagate inside the domain to interact with the building. The incident flow is successfully modelled, in terms of mean, turbulence intensity and spectral content. Mean, standard deviations and peak pressure coefficients correlate well with experimental results and the procedure is advantageous compared to similar computational techniques. The target accuracy is achieved, benefits and limitations of the method are discussed, and conclusions based on experimental and computational observations are drawn.

Study on VIV Behavior of Two 5:1 Rectangular Cylinders in Tandem Based on Correlation Analysis

To investigate the vortex-induced vibration (VIV) characteristics of two rectangular cylinders with a width-to-depth ratio of 5:1 in a tandem arrangement, sectional model wind tunnel tests that measure vibration responses and pressure distributions simultaneously were adopted. The ratio of the spacing between the cylinders to its width is 1.2. The analyses were performed considering VIV responses as well as the distribution characteristics of mean and rms pressure coefficients. Additionally, the time-frequency domain statistical parameters like correlation and contribution coefficients, phase lags between distributed and general vortex excited forces (VEFs), and amplitudes of VEF coefficients at predominant frequencies were calculated to analyze the physical VIV mechanism of two 5:1 rectangular cylinders in tandem. This study indicates that the influence of incidence angles on the dynamic responses is notable; the contribution of the distributed VEFs acting on the trailing surface of the upstream cylinder and the leading surface of the downstream one is significant to VIVs of the cylinders from wind pressure distribution characteristics and correlation analyses.

Flow-induced vibration and heat transfer in arrays of cylinders: Effects of transverse spacing and cylinder diameter

This two-dimensional numerical study investigates flow-induced vibration (FIV) and heat transfer in 3 × 3 arrays of nine heated circular cylinders of equal and unequal diameter configurations at a constant Re = 100. Six out of the nine cylinders are stationary, while three are elastically supported in the vertical direction. The computations are carried out using the commercial software ANSYS Fluent loaded with user-defined function (UDF). The effects of transverse spacing ratio (G* = 2, 3, and 4), diameter (D) and reduced velocity (2 ≤ Ur ≤ 20) on time histories of cylinder displacements, vorticity contours, oscillation amplitudes, mean pressure coefficient and Nusselt number (Nu) are investigated by considering forced convection heat transfer. Results show that lower oscillation amplitudes of elastically supported cylinders are noticed in arrays of cylinders when all cylinders are placed closely, i.e., at G* = 2. Furthermore, as G* increases, the oscillation amplitudes also increase due to the formation of vortex shedding. A better heat transfer performance is observed for arrays of cylinders with varying diameters at G* = 2 compared to those with the same diameter. For G* = 4, arrays of cylinders with the same diameter possess better heat transfer for all Ur. FIVs affect the Nu of elastically supported cylinders as well as stationary cylinders.

Anticipating Surface Mean Pressure Coefficient on Inner Surface of C-Shaped Irregular Buildings Using Artificial Intelligence Methodology

Anticipating Surface Mean Pressure Coefficient on Inner Surface of C-Shaped Irregular Buildings Using Artificial Intelligence Methodology

NUMERICAL MODELLING OF WIND LOADS ON WINDOWS. VALIDATION FOR A HIGH-RISE SQUARE PLAN BUILDING

This paper presents the results of numerical and experimental modelling of mean and peak pressure coefficients for window assemblies on a rectangular building. The applicability of the SST and GEKO k-ω turbulence models implemented in ANSYS Fluent is investigated. A simple steady-state method for determining the peak wind pressures, which utilizes the turbulence kinetic energy calculation, is shown to be sufficient for practical purposes. A comparative analysis with the values of pressure coefficients given in the Russian building code is carried out. The obtained results can be used in the design of window assemblies of typical buildings.

Effects of Cornices on Wind Loads of Solar Panels Mounted on Gable Roof Building

The effects of various parameters of the solar panel and surrounding structure on wind loads acting on solar panels have been extensively investigated in prior studies. However, the parameter of cornice length has not been considered. With varying lengths of cornices, solar panels can be positioned either near or far away from the roof corner and edge, which are the locations where the largest wind-induced suction forces are likely to occur. To examine the effects of cornices, a wind tunnel test was conducted to measure the wind pressures on a solar module installed on a residential gable roof building. The cornice lengths varied from 0 m to 1.6 m, with an interval of 0.4 m. The results show that when wind blows perpendicular to the roof ridge, cornice can reduce the mean, STD, and peak pressure coefficients on the upper and lower surfaces and resulting net values. However, it should be noted that the most unfavorable area-averaged minimum peaks in the middle and trailing zones exhibit a gradual increase with the growing cornice length. Considering the potential risk of solar module failure resulting from high wind-induced suction forces, more caution is needed when installing solar modules on roofs with larger cornices.

Shape optimization of a corner‐recessed square tall building to reduce mean wind pressure using a multi‐objective genetic algorithm

SummaryThe current study aims to determine how the corner recession affects tall buildings with square plans. A series of numerical simulations have been conducted to find the parametric models' wind pressure. Visualization tools, such as contour plots and streamlines, present the wind flow near the buildings. Numerical simulations are conducted using RANS k‐ℇ turbulence models considering a length scale of 1:300. Subsequently, a shape optimization study has been carried out to propose a suitable percentage of corner recession, which should minimize the wind pressure on different faces of the building. As design factors, the amount of corner recession (S) and the wind incidence angle (Ø) are taken, along with the mean pressure coefficients (Cp) on the various building faces. Due to the eight axes symmetry of the building configuration, the random sampling technique is used for the Design of Experiment while accounting for the 0°–45° wind angle of attack. The Response Surface Approximation (RSA) is used to construct surrogate models of the objective functions. The RSA models are validated with wind tunnel test results presented in previously published articles. The optimization study is carried out using the multi‐objective genetic algorithm technique.

Association between serum 25-hydroxyvitamin D concentrations and hypertension among adults in North Sudan: a community-based cross-sectional study

BackgroundGlobally, hypertension represents a major public health problem. The association between 25-hydroxyvitamin D (25[OH]D) levels and hypertension remains unclear. The current study aimed to investigate the association between serum 25(OH)D levels and hypertension among adults in Sudan.MethodsA community-based cross-sectional study was conducted among adults in North Sudan. Sociodemographic and clinical data were collected using a questionnaire and face-to-face interviews. Serum 25(OH)D was measured using an enzyme-linked immunosorbent assay. Multivariate logistic regression and multiple linear regression analyses were performed.ResultsOf the total of 391 participants, 202 (51.7%) were females. The median (interquartile range [IQR]) of participants’ ages was 45(32–55) years. Of the total, 219(56.0%) had hypertension. The median (IQR) of serum25(OH)D was 13.3(9.9–19.7) ng/mL, and 295 (75.4%) participants had vitamin D deficiency (< 20 ng/mL). In multivariable logistic regression, the adjusted odds ratio (AOR) for age = 1.05, 95% confidence interval (CI)1.03‒1.061, the AOR for being female = 2.02, 95% CI, 1.12‒3.66, and body mass index was AOR = 1.09, 95% CI, 1.05‒1.14, all of which were significantly associated with hypertension. However, serum 25(OH)D levels were not associated with hypertension (AOR = 1.01, 95% CI 0.99‒1.05, P = 0.317). In multiple linear regression, while systolic blood pressure was negatively associated with 25(OH)D (coefficient = − 0.28, P = 0.017), there was no significant association between serum 25(OH)D level and diastolic blood pressure (coefficient = − 0.10, P = 0.272) or mean blood pressure (coefficient =–0.03, P = 0.686).ConclusionThe current study revealed a negative association between vitamin D and systolic blood pressure. The mechanism of such an association needs further study.

Exploring the impact of vertically separated flows on wind loads of multi-level structures

The complex dynamics of vertically separated flows pose a significant challenge when it comes to assessing the wind loads on multi-level structures, demanding a nuanced understanding of the intricate interplay between atmospheric conditions and architectural designs. Previous studies and wind loading standards provide insufficient guidance for designing wind pressures on multi-level buildings. The behavior of wind around perpendicularly attached surfaces is not quite similar to that of individual flat roofs or walls. When a body is composed of several surfaces with right or oblique angles, the separated flow from surfaces and their interactions will cause complex flow patterns around each surface. A wind tunnel experimental study was carried out on bluff bodies with attached flat plates and other adjacent bluff bodies with different heights to examine the wind-induced pressures on such complex shapes. Mean and peak pressure coefficients were measured to determine the flow interaction patterns and location of localized peak pressures. The results were compared to the Tokyo Polytechnic University Aerodynamic Database of isolated low-rise buildings without eaves. The research findings indicated that there was a noteworthy disparity between the minimum and maximum values and locations of peak pressures on both the wall and roof surfaces of the models used in this study, as compared to the results obtained by the Tokyo Polytechnic University. Moreover, the study conceivably pointed to the difference between the peak negative and positive pressure coefficient locations with the ASCE 7-22 wind loading zones. The peak suction zones were affected by the combined flows at perpendicular faces, and as a result, different wind load zones were obtained dissimilar to those introduced by ASCE 7-22. Wind loading standards may need to be modified to account for the wind pressures on complex building structures with an emphasis on the location of the peak negative pressure zones.

Experimental study on distributed aerodynamic forces of parallel box girders with various slot width ratios and aerodynamic countermeasures during vortex-induced vibration

The widespread adoption of parallel box girders in bridge engineering is attributed to their superior traffic-bearing capacity and streamlined construction methodologies. Nevertheless, these structures are confronted with exacerbated vortex-induced vibration (VIV) challenges stemming from aerodynamic interference and intricate vortex shedding phenomena between the girders. In the present study, a series of extensive wind tunnel experiments are conducted to scrutinize the VIV behavior of parallel box girders with diverse slot width ratios, taking into account both sectional model oscillations and surface pressure. The mean pressure coefficient, fluctuating pressure coefficient, time-frequency attributes of the distributed aerodynamic force, and the contribution value of distributed aerodynamic force to vortex-driven force are meticulously analyzed and compared to ascertain the impact of slot width ratio on VIV. Drawing on the empirical findings, we put forth and assess aerodynamic countermeasures aimed at augmenting the VIV performance of parallel box girders. Furthermore, the control mechanism for VIV is studied with respect to alterations in the distributed aerodynamic force. Our investigation reveals significant aerodynamic interference between parallel box girders featuring distinct slot width ratios. The frequency multiplication effect and signature turbulence in the aerodynamic force amidst VIV is observed, although the oscillation characteristics persist primarily at a singular frequency. The VIV of parallel box girders is instigated by the marked fluctuating pressure on the upper surface in proximity to the slot side and the inclined web of the leeward girder, accounting for the heightened severity and intricacy of VIV in these configurations as opposed to single closed-box girders. The synergistic implementation of skirt plates and wind fairings or winglets efficaciously eradicates the root causes of VIV in the original girders and even transmutes the contribution value of the distributed aerodynamic force from positive to negative, thereby suppressing VIV.

Flow-induced forces and vortex transportation characteristics of three circular cylinders at subcritical Reynolds number

Three-dimensional numerical simulation for the three circular cylinders at Re = 3900 is carried out by using the large eddy simulation (LES) in this paper. The present numerical model and parameters are verified by solving single cylinder and two cylinders cases. Then, the parameters consisted of spacing ratio (L/D) and incidence angle (α) are checked in three circular cylinders array. The fluid force and near-wake behavior of the two- and three-cylinder systems are analyzed with emphasis. Under a tight arrangement, there are three flow patterns: reattachment flow pattern, large-incidence-angle flow pattern, and biased flow pattern, corresponding to cases with incidence angles of 0, 45, and 90 degrees, respectively. The Strouhal number (St) of the three cylinders is essentially overlapping at α= 0° and α= 90°, the distinctive secondary peaks can be observed at the small spacing ratio in power spectral density (PSD). The mean pressure coefficient of midstream cylinder (MC) influenced by the number of cylinders is negative in the tandem arrangement at the stagnation point, accompanied by reattachment phenomenon the upstream surface of MC with L/D= 1.5. Placing the third cylinder between the two cylinders in a tandem arrangement significantly suppresses their lift oscillations. The phase difference (φum) between the fluctuating lift of the upstream two cylinders is highly sensitive to the incidence angle of the system.