Negative Wind Pressure Research Articles

High-resolution flexible iontronic skins for both negative and positive pressure measurement in room temperature wind tunnel applications

Flexible skins that can be laminated on curved surfaces are a desired form for wind pressure measurement. Sensors for such applications need to detect both negative and positive wind pressure with ultrahigh pressure resolution over a wide range up to 600 kPa, whereas existing flexible sensors are unsatisfactory to such demands. Here, we report a flexible skin containing two iontronic pressure sensors for negative pressure and positive pressure sensing, respectively, and show the potential of the skin for pressure measurement in room temperature wind tunnels. We control the contact state of iontronic interface of a sensor to introduce a pre-pressure that enables negative pressure sensing, exhibiting a pressure resolution of −20 Pa (0.025%) within a broad pressure regime (from −100 kPa to −10 Pa). The other sensor for positive pressure sensing exhibits a pressure-resolution of 100 Pa (0.025%) over 600 kPa, in addition to a wide frequency bandwidth up to 400 Hz. The skin with the two types of sensors can be attached on curved surfaces of wing surface for pressure measurement at various free stream velocities and angles of attack. This study provides a promising technology of using flexible skins for pressure measurement in aviation applications.

Average surface wind pressure surrounding tall buildings with cruciform shapes

Abstract Building shape affects wind pressure on building surfaces, while limited studies have examined how building shape affects the wind pressure on cruciform-shaped tall buildings. This article investigated the variation of the average wind pressure coefficient (AWPC) on cruciform-shaped tall buildings with the height–width ratio (HWR) and height–thickness ratio (HTR). The results demonstrated the occurrence of building blockage, wind separation, wind re-circulation, and wind re-attachment on building surfaces. The frontal surface of the main building was always the windward surface with positive wind pressure. At 2/3 of the building height (H), the peak AWPCs in all scenarios were ~0.70. However, in the case with an HWR of 3.66, the side surfaces of the main building and the frontal surfaces of the branch building, wind pressure was all negative. With the HWR reduction by building width increase, wind pressure on these surfaces became positive, where the AWPCs in the HWR = 1.41 case were 0.60–0.63 and 0.64–0.69 on side and frontal surface, respectively. With the HWR decrease, both positive and negative wind pressure intensified. Along the central axis (M1) in the vertical direction, wider buildings had stronger positive wind pressure on the frontal surfaces below 0.10H, while narrower buildings had stronger positive wind pressure above 0.82H. In comparison, HTR made limited differences to the wind pressure on the frontal surface. Overall, vertical results showed that scenarios with smaller HWR underwent stronger positive and negative wind pressures. On the HTR cases, wind pressure on top surfaces showed complicated results, while thicker buildings had weaker negative wind pressure on the back surface. Overall, this study is important to understand the characteristics of wind load on cruciform-shaped tall buildings and generate implications for wind resistance, natural ventilation design, and wind electricity generation over tall buildings.

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.

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.

Wind Tunnel Experiments on Interference Effects of a High-Rise Building on the Surrounding Low-Rise Buildings in an Urban Block

High-rise buildings cause accelerated winds around them. However, the interference effects of high-rise buildings on the surrounding low-rise buildings in urban blocks have not been evaluated. This study investigated the wind pressure coefficients on the roofs and walls of low-rise buildings surrounding a high-rise building through wind tunnel experiments. Seventy-two wind directions were considered from 0° to 355° in 5° increments, and the influence of the wind direction on the wind pressure coefficients of surrounding buildings was evaluated. At a 30° wind direction angle, the positive and negative peak wind pressure coefficients occurred in a low-rise building at the leeward side of the high-rise building. The positive peak pressure, approximately 1.4 times that without a nearby high-rise building, occurred at the windward corner on the front wall of a low-rise building. The negative peak value, approximately three times that without a nearby high-rise building, was observed at the windward edge on the roof of a low-rise building. Thus, accelerated winds caused by high-rise buildings may result in unexpected damage to the surrounding low-rise buildings.

Effects of Vertical Rib Arrangements on the Wind Pressure and Aerodynamic Force of a High-Rise Building

Façade appurtenances such as vertical ribs are increasingly used on high-rise buildings to enhance the architectural appearance. These attached ribs may modify the wind pressure acting on a building by changing the local flow pattern around the building. This study investigated the effect of the extensional depth of the vertical rib on the wind pressures of a high-rise building with a square cross-section. The wind pressure distribution on different surfaces, layer force coefficient, base shear coefficient, and base bending moment coefficient were analyzed under various rib extensional depths. Moreover, the measured layer force coefficients along the heights were compared with those provided by the current codes. This study’s results show that when the building is under normal approaching flow, the negative pressure area on the front surface increases with the rib extensional depth (b). This may be induced by the local recirculation at the outermost vertical ribs, which enhances the flow separation around the building. The negative wind pressures on the leeward surface show a slight increase with the increase in the rib extensional depth. Compared to the test results, the resultant layer force coefficients provided by EN 1991-1-4:2015 and GB 50009-2012 are conservative while those from the wind effect code of Hong Kong 2019 result in an underestimated evaluation. Increasing the extensional depth of the attached vertical rib may significantly reduce the positive layer wind pressure on the windward surface by 28% but increase the negative layer wind pressure on the leeward surface by 17%. The installation of vertical ribs with a small external depth (e.g., b is less than 2% of the building width) may exert limited effects on the overall base shear and bending moment, but the maximum base shear and bending moment will be reduced by 8.8% and 7.4%, respectively, when b increases to 4% of the building width.

Numerical Simulation and Wind Tunnel Test on the Wind-Induced Response of Three Typical Types of Greenhouse Main Structures

Investigating the wind-induced vibration response of the greenhouse structure, and the wind pressure distribution on its surface takes on a critical significance when the main structure is under large wind loads. A computational fluid dynamics-based study was conducted, and wind tunnel tests were performed to study the wind pressure distribution on the surface of the greenhouse structure. First, three types of greenhouses, including Venlo, Round-arch, and Saw-tooth type greenhouses, were selected as the design models for the study. In addition, the double-span, four-room structure model was built to explore the wind pressure distribution and the extreme wind pressure coefficient on the greenhouse surface for 13 (0°–180°, every 15°) directions of the wind direction to obtain the wind load characteristics in the greenhouse surface under different conditions. The results of the wind tunnel tests were consistent with those of the simulations, with the maximum wind pressure in the X-direction occurring at 30°-wind and the maximum wind pressure in the Y-direction at 75°-wind. The maximum negative wind pressure acting locally on the roof of the greenhouse was twice the maximum positive pressure acting on the windward side of the greenhouse. Accordingly, it is necessary to strengthen the structure in regions sensitive to wind direction with significant response to wind.

Numerical study on aeroelastic behavior of spoiler on low-rise building based on fluid-structure interaction method

Technical mitigation devices have been demonstrated to be efficient for decreasing the peak and mean wind pressures on the roof systems of low-rise buildings through disrupting vortex formation. Previous investigations have regarded mitigation devices as rigid bodies and neglected aeroelastic behavior. However, the relatively large uplift force induces small-stiffness mitigation devices vibration and introduces a considerable aeroelastic effect. These effects might result in an increase in negative wind pressure on the building roof and the aeroelastic instability problems of mitigation devices. Therefore, the current study conducted two-way fluid-structure interaction (FSI) numerical simulation for a low-rise flat-roof building with mitigation devices (metal and polymer spoilers) to investigate the influence of the aeroelastic effect of spoiler on the wind pressure on the building roof. The large eddy simulation (LES) method and the finite element analysis (FEA) model are used to solve the flow field and the structural responses of the spoiler, respectively. The computational model and method are verified by comparing the calculation results with previous experimental results and benchmark computational tests. The dynamic response of spoiler, the flow instabilities and the wind pressure on the building roof are analyzed. The influence mechanism of the spoiler vibration on the flow field over the building, the wind pressure on the building roof and the uplift force on the spoiler were revealed considering the influencing factors, including the vibrational amplitude of spoiler and the wind direction. The results show that the aeroelastic effect of spoiler increases the negative wind pressure on the roof, and the larger the vibrational amplitude of spoiler is, the more the negative wind pressure increases. The negative wind pressure on the eave also increases with increasing wind direction angle. The main reason for this phenomenon is that the spoiler vibration increases the degree of flow separation over the building roof.

RESEARCH ON WIND PRESSURE DISTRIBUTION OF PLASTIC GREENHOUSES IN VALLEY TOPOGRAPHY

As the wind pressure distribution on plastic greenhouses in valley areas is different from that of greenhouses on plains, it is necessary to find out the variation trend of the wind pressure coefficient on greenhouses in the valley areas. Based on the ‘Realizable k-e turbulence’ model, the wind pressure characteristics on plastic greenhouses located in valley and plain areas are studied by using the verified numerical simulation method. The wind pressures on greenhouses and the corresponding fitting formula are obtained for different distances between the greenhouse and the foot of the mountain with a 0-degree wind angle. The results show that, with an increase of distance to the mountain, the positive wind pressure on the windward side of a plastic greenhouse increases and the negative wind pressure on the leeward side, roof surface and crosswind sides of the greenhouse decreases. The results from the proposed formulae are very close to those derived from the numerical simulation method, and the relative errors are all within 10%. The influence of canyon wind on the wind pressure distribution on plastic greenhouses should be considered in the design. This research can provide a reference for the wind resistance design of plastic greenhouses built in valley areas.

Effects of Interference on Local Peak Pressures Between Two Buildings with an Elliptical Cross-Section

Abstract The interference effects on the distribution of external wind pressure coefficient between two high-rise buildings with an elliptical cross section were studied experimentally at the Boundary Layer Wind Tunnel (BLWT) at the Faculty of Civil Engineering STU in Bratislava, Slovakia. Various arrangements of models, which were derived from the breadth ratio, were investigated. The peak value of the external wind pressure coefficient for a stand-alone model was measured and compared with the peak value in the case of interference. The measurements showed that the wind loads on buildings in a close vicinity are considerably different from those on a stand-alone building. The interference effects significantly affect negative pressure zones. The optimal and critical arrangements of buildings were evaluated. The elimination of peak negative external wind pressure coefficients can be reduced by half. On the other hand, the interference effects had a strong impact on increasing the peak value of the negative external wind pressure coefficient, which can be more than roughly double compared to an isolated building.

Study of Interference Effect of Wind Pressure on Roof of Multi-storey Residential Buildings

In this paper, a series of wind tunnel experiments were carried out on the rigid model of 5-6 storey residential buildings to study the influence of the location, spacing and wind direction of the buildings on the roof wind pressure of multi-storey residential buildings. The test results show that the maximum average wind pressure and extreme negative wind pressure of a single building occur in the roof ridge area at the corner and both ends of the roof, taking a multi-storey building with length × width × height of 60m×12m×20m as an example. For the buildings with three rows and three columns, when the building is located at the corner, the most unfavorable wind direction is 30°, 210°, and 330°. The most unfavorable extreme value of negative wind pressure is -8.72. The negative wind pressure coefficient of the most unfavorable extreme value of the building roof at the corner position and the middle position of the first row decreased with the length-width ratio and the spacing increased. The negative wind pressure coefficient of the most unfavorable extreme value of the building roof at the edge and middle of the second row did not change significantly with the increase of length-width ratio but increased with the increase of space. In the corner area of the roof, the interference factor of the corner position and the middle position of the first row decreased with the space, while the interference factor of the edge position and the middle position of the second row increased with the space. The variation trend of the middle area of the roof is the same as that of the corner area, but the interference factor is generally small. The interference factor of the wall area is always greater than 1.0.

Experimental studies on column foot connections of novel fully enclosed noise barriers

This paper investigates the static and fatigue behaviors of the column foot connection of a new fully enclosed noise barrier before it can be put into practice. This barrier was designed for freight railway bridges passing through city ecological areas to satisfy the high environmental assessment requirements in China. Because the height of the noise barrier reaches over two times the normal size, the column foot is tentatively connected with four high-strength U-bolts embedded in a concrete block located at the flange end of the railway box-girder bridge. A segmental full-scale static model test was performed to inspect the overall resistance of the connection. Then a fatigue test focusing on an interception column foot connection model considering the positive and negative pulsating wind pressure generated by the train was performed. The equivalent fatigue amplitude was determined by the internal force spectrum of a passing train at the column base. The results were compared with different scales of detailed FE models and discussed based on the given specifications. Instead of fatigue or strength damage, the column base bolts are more likely to become slightly loose when subjected to a period of large fatigue loads. Thus, such types of bolt connections should be inspected regularly for strict control of the tightening torque.

Load carrying capacity of greenhouse covering films under wind action: Optimising the supporting systems of greenhouse films

The load carrying capacity of a typical greenhouse film used as covering for a Gothic-type greenhouse was investigated under negative wind pressure. The film was simulated as a membrane through appropriate shell elements and analysed with the finite element method (FEM). The design wind pressures were calculated based on the provisions of Eurocode 1 and EN13031. The FEM model boundary conditions corresponded to the real film supporting conditions of an industrial type greenhouse structure. The film was pre-tensioned at its initial state in the longitudinal direction, and then subjected to uniform negative wind pressure. The nonlinear elastic analysis with large deformations results showed that, as the wind pressure increases, the principal tensile stress in the film increases and gradually reaches the material stress at yield value. Plastic deformation is expected to take place and the film loses its capacity to return to its initial undeformed state. Consequently, the plastically deformed film loses its prestress state and its proper elastic behaviour. Depending on the final wind pressure intensity and the degradation condition of the film, premature failure may therefore occur. The analysis revealed that the film failure is due to insufficient supporting of the film on the steel structure. This behaviour was verified by examining a real greenhouse film failure case. Various supporting systems of the greenhouse covering films with additional intermediate supports were analysed and optimal design solutions are proposed. The proposed optimised supporting systems of greenhouse films covers a gap in the current European standard for greenhouse design.

Assessment of the Wind and Temperature Loads Influence on the PVC Windows Deformation

The PVC windows application experience in various climatic conditions shows that at their operation the windows profile deformations can be observed. One of the reasons for these deformations is the climatic loads influence on the windows – wind pressure, solar radiation, negative outside temperatures. The profile elements deformations affect the window tightness and the normal window hardware operation. The calculated loads combinations on windows in winter and summer were analyzed. For window as external element of building is more critical winter loads combination – the combined effect of wind pressure and negative temperature. The work was done the analysis of the effect of negative temperatures and wind pressure on the PVC window deformation. The studies were performed in laboratory conditions on the basis of two testing centers. Three PVC Windows with different profile thickness were tested. The temperature deformation of the casements and mullions profiles of this windows were analyzed. These deformations have to take into account in the static calculations. But the engineering methods creation for calculating windows for the wind and temperature loads effect requires additional research. They are associated with the study of the joint work of the windows constituent elements (profiles, insulating glass units, hardware).

Influence Of Sashes Stiffness On PVC Windows Resistance To Wind Load

Nowadays, the calculation of wind load on PVC window units is carried out according to a simplified method, without taking into account the stiffness of PVC profile elements and the joint actions of their load-bearing elements (imposts) and sashes. The introduction of a refined methodology for the calculation of PVC window units, concerning the above factors, will reduce specific consumption of materials and the cost of products. In this work, we do research about this issue. Laboratory tests were conducted on typical designs of PVC window units to test the effect of wind loads. Various configurations of PVC window units (with different types of reinforcing profiles of sashes and imposts, fixed window, etc.) were examined under different wind pressures. The test results were compared with the theoretical calculations. It is established that the effect of the sash on the deflection of the calculated elements of the window unit is significant, and the theoretical calculations do not coincide with the test results. The model of the PVC window unit operation is described under the action of positive and negative wind pressure, taking into account its components - PVC profiles, reinforcing profiles, insulating glass units, etc. The directions of further research of this issue are suggested.

Wind Pressure Mitigation on Gable Roofs for Low-Rise Buildings Using Spoilers

AbstractPrevious wind disaster investigations have indicated that the roof systems of low-rise buildings often suffer severe damage under the negative wind pressure caused by the sharp corners betw...

Sensitivity analysis of wind pressure coefficients on CAARC standard tall buildings in CFD simulations

Constructing tall buildings has been a common trend for many cities due to rapid increase of population, therefore, it is essential to analyze wind pressure around and over these tall buildings. CFD simulation is an effective approach to realize this, in which CAARC (Commonwealth Advisory Aeronautical Research Council) standard tall building has been a well-acknowledged model to validate and calibrate tall building models. Nevertheless, less work has been conducted to study sensitivity of wind pressures over CAARC standard tall building to geometric and computational parameters in CFD simulation. This paper is therefore designed to fill this gap by analysing impacts of various parameters like turbulence model, approaching-flow speed and grid type on wind pressure coefficients over CAARC buildings. In this paper, wind pressure coefficients over CAARC models subjected to four wind directions were numerically analyzed for validating the correctness and effectiveness of numerical model. Sensitivity of wind pressures to geometric and computational parameters was analyzed through comparisons of deviation and absolute deviation. Results indicated that various phenomena such as fluid separation, vortex, wake effect and reattachment were sensitive to wind direction, resulting in great variations in wind pressure. Maximum positive wind pressure coefficients emerged around 0.8–0.85H of windward surface, while maximum negative one occurred at foreside of top surface. Furthermore, turbulence model had significant influences on the accuracy of numerical results, where Realizable k-ε and SST were the most accurate turbulence models, and standard k-ε and RNG k-ε models were the second accurate ones, but BSL was not recommended for wind resistance design. Approaching-flow speed and grid type exerted insignificant influences on pressure coefficient distribution, while grid resolution had significant effects on negative wind pressure distribution. In general, conclusions obtained in this study can assist structural engineers to select practical geometric and computational parameters in predicting wind pressure distribution against tall buildings.

Interference effect and the working mechanism of wind loads in super-large cooling towers under typical four-tower arrangements

Group tower-related interference is one of the major causes of wind-induced damage of large cooling towers. The four-tower arrangements are the most common forms of the layout of group towers. In engineering practice, five arrangements are generally used, namely, single row, rectangular, rhombic, L-shaped, and oblique L-shaped. We performed wind tunnel tests on the rigid body to study the static, dynamic and extreme interference effects under these five arrangements. Then the computation formulas of interference factor that accounted for the wind directions under the five arrangements were proposed. The effects of four-tower arrangement on the distribution patterns of mean and pulsating wind pressures were discussed. The wind pressure signals at the typical measurement points of the cooling towers were subjected to decomposition and joint time-frequency analysis using mathematical statistics technique and Hilbert-Huang transform (HHT). The study shows that the maximum interference factors under the five arrangements were all higher than those under the layout of two towers. It is reasonable to use the extreme interference factor as the measure of the interference effects. The maximum positive pressure of the cooling towers was less affected by the interference effects related to four-towers, and the mean wind pressure were affected greatly in the regions of minimum negative wind pressure and leeward regions. The distribution patterns and values of pulsating wind pressures at the bottom and top of the cooling towers were significantly affected by the five arrangements of the cooling towers. Finally, based on comprehensive assessment of the interference effects of overall wind loads, arranging the four towers in a row was the best scheme, which was followed by the arrangements in oblique L-shaped pattern, L-shaped pattern, rhombic pattern and rectangular pattern successively.

Investigation on wind tunnel tests of the Kilometer skyscraper

Wind tunnel tests were carried out to investigate the wind pressure distribution of a super high-rise building with a height of 1040m in China. The huge model size led to several technical difficulties, including simulation of large scale wind flow fields, correction of distortion effects caused by tubing systems and synchronization correction for data in batches. To simulate the wind field with an elevation of one kilometer above the ground, custom designed grid and roughness elements were adopted as flow-adjustment passive devices. According to the matrix transfer method, a set of transfer functions for tubing systems with different lengths were established to eliminate the effect of distortion on fluctuating pressure measurement. A correction method based on Generalized Regression Neural Network (GRNN) was proposed to get time-synchronized data of the whole building. After solving these problems, the mean and extreme pressure coefficients were studied for the distribution of wind-induced pressure. For this model with triaxial symmetry, the distribution of wind pressure shows good symmetry. With the increase of height, largest peak positive wind pressure coefficients increase, while smallest peak negative wind pressure coefficients decrease. The solutions to technical problems and the outcome of wind pressure distribution are expected to be useful to engineers and researchers involved in this field.

Numerical study of lift and drag coefficients on a ground-mounted photo-voltaic solar panel

A comprehensive numerical study has been carried out for the wind effects on a standalone ground-mounted solar photo voltaic (PV) panel in various wind directions. PV panels are vulnerable to wind loading and extensive damages have been reported the world over, due to high wind. No wind-related design guidelines and codal provision are available, for the design of PV panels. Computational Fluid Dynamics (CFD) techniques using Reynolds-Averaged Navier-Stokes equations (RANS), has been used to predict the drag and lift coefficients on the inclined PV panel subjected to the wind incident angle of 0° to 90° for the turbulent wind flow.The drag and lift, in x and y directions respectively, are found to be maximum when the wind is flowing normally to the PV panel, whereas the lift in the z-direction is maximum when the wind incident angle is 60°. The maximum positive and negative wind pressure coefficient on the windward side of the PV panel has been found as 1.120 and -0.716 at the wind incident angle of 60° and 90° respectively. Whereas, the maximum positive and negative wind pressure coefficient on the leeward side of the PV panel has been found as 0.020 and -4.914 at the wind incident angle of 0° and 45° respectively. The results can be concluded that the PV panel is subjected to significant lift and drag force under wind loading, which may cause damage to the PV panel if it is not designed properly.