Windward Face Research Articles

Study of wind loads on rectangular plan tall building under interference condition

The change in distribution of wind pressure due to alteration of wind flow pattern caused by the existence of an interfering building is explored in this study on a principal tall building having cross-section of rectangular shape. Interfering building having same cross-sectional shape as the principal building but a variation in height is placed in-front of the principal building, with across-wind lengths of two buildings being in-line with each other. Keeping the principal building fixed in position, the spacing between two buildings is varied by changing the position of interfering building, so as to understand the effect of spacing and height variation upon the wind loads and pressures. Two independent type of measurements are undertaken for varying interfering building height: (1). Force Measurement (2). Pressure Measurement. For purpose of validation, the results obtained from two independent measurements mentioned are compared later. The results obtained from force measurements are expressed in the form of two-dimensional X-Y plots, while that for pressure measurement are depicted in the form of mean and RMS wind pressure coefficient (CP and CP') contour plots on all vertical faces of the principal building. Force measurement results show that the interference effect subsides as the interfering building height is reduced and spacing is increased. However, from pressure contours it is evident that when the interfering building is close to principal building pressure force on the windward face reduces while the suction on the leeward face increases with the reduction in interfering building height. Negative drag is also observed for few of the cases.

Drag reduction of a square-back bluff body under constant cross-wind conditions using asymmetric shear layer forcing

Highly resolved computations using Delayed Detached Eddy Simulations (DDES) of a canonical Windsor body are carried out. The flow around the car model, which is investigated imposing different yaw angles (up to 10°), is perturbed via a small square cylinder. This control element, whose length covers the whole height of the car model, is positioned at different streamwise locations on the windward face of the model. Depending on the location of the cylinder and the initial yaw angle of the model, drag increase or decrease up to 8% are observed. This sensitivity of the drag to the streamwise location of the cylinder is connected with the relative position of the flow reattachment on the side of the model after separation, which is caused by the cylinder. In the drag-optimal case where the flow reattachment occurs just at the streamwise location of the base, the asymmetry of the wake is reduced and the pressure in the wake is globally recovered. The flow mechanisms by which the drag reduction occur are twofold: (i) the flow is deviated inwards by the in-wash induced by the flow reattachment at the trailing-edge, thus acting as an inward-oriented flap, and (ii) the windward shear layer is forced by the turbulent field developing along the separated region of the perturbing cylinder.

Suppression of Wind Waves in the Presence of Swell: A Physical Modeling Study

AbstractLaboratory measurements of the interaction between high‐frequency (HF) wind‐waves and low frequency (LF) paddle waves are presented. The measurements were made in a wind‐wave flume with wind and paddle waves propagating in the same direction. The primary objective is to examine the physical mechanisms proposed to explain the suppression of wind‐waves due to presence of swell (here paddle waves). For this purpose, the precise time scale of the temporal transition from wind‐only to wind‐plus‐paddle conditions is examined. The results reveal that the majority of wind‐wave suppression occurs too quickly to have been caused by reduced wind‐input, instead indicating that enhanced HF wave dissipation is the primary suppression mechanism. The spatial variation in HF wave energy along the LF wave phase indicates that HF suppression mainly occurs on the LF wave crest, and high on the windward face, which are the locations that experience the highest wind velocities. This observation also suggests that the reduced wind‐input is not the primary suppression mechanism. Quantification of HF wave suppression versus a broad range of wind velocities, paddle wave conditions and fetch did not reveal any critical dependence of suppression on LF wave breaking or wind separation at LF wave crests. It is concluded that suppression occurs primarily due to enhanced dissipation of HF waves near LF wave crests. This mechanism is proposed to be coupled to the wind velocity, where an increased wind velocity near LF wave crests exceeds the level of forcing that HF waves of low C/u* can withstand without breaking.

Effect of Interference Between Twin Tall Buildings with Recessed Corners on Wind-Induced Pressure

This paper investigates the results of wind tunnel model testing on pressure distribution and proximity effects between twin tall buildings with large recessed corners in an open circuit boundary layer wind tunnel. Experiments were carried out for isolated and for full, half and no blockage interference conditions. Three interference conditions were created by placing the building of identical shape and size at different locations on the windward side of the principal building under consideration. Based on the experimental results, mean and Root Mean Square (RMS) wind pressure coefficients and interference factors are presented and discussed for all cases. Mean wind pressure coefficients and interference factors at all faces of the building model are plotted in the form of contours and also plotted along the height of the building at all faces. Pressure coefficients and interference factors for three interference conditions are also compared with the results of isolated condition to bestow comprehensive evaluation of the effects of the interference on changing of wind loads. Results show that pressure coefficients variation greatly depends on the position of the interfering building. Oblique configuration produces more severe interference effects on windward surfaces. The re-entrant corners present in the model also affect the pressure distribution because of flow stagnation in these corners. The interference effects in no blockage condition are significant and unfavorable at windward faces near recessed corners towards the interfering building, where the mean interference factor of more than 13 is observed.

Wind Loads on Solar Panels Mounted on Facade of High-Rise Residential Building

Wind effects on solar panels mounted on façade of high-rise residential building are studied through wind tunnel test. The model with scale ratio of 1:80 is adopted. Results show that the top floor panel is dominated by the upward negative wind load, and the panel at the mid height floor suffers the downward positive wind load, when the panels are mounted on the windward face. The influence of different inclination angles on force coefficient of the panel is also studied. It is found that positive peak force coefficient increases with the increase of panel’s inclination angle, most unfavorable extreme wind suction decreases with increase of panel’s inclination angle. Results show that the location of panels has significant effect on the design wind load. The peak force coefficient values of [Formula: see text] and [Formula: see text] can be used as the recommended values for design wind coefficients of the top floor panels. Peak force coefficient values of [Formula: see text] and [Formula: see text] can be used as the recommended values for design wind coefficients of the mid floor panels. The correlations between wind loads on different panels are also examined to check the flow mechanism around the panel. Different trends can be clearly checked from the results for different incident wind directions, suggesting the complex flow condition near panels. The greater the panel inclination is, the higher the correlation of net force coefficient between two adjacent panels is.

Effects of facade rib arrangement on aerodynamic characteristics and flow structure of a square cylinder

Ribs on building façade can reduce wind loads acting on high-rise buildings and modify the corresponding flow structures. The present study investigates the effect of vertical ribs with different arrangements on the flow field and aerodynamic characteristics of a square cylinder under uniform flow by using LES. The results show that the windward face ribs and downstream ribs of sidewall can obviously affect the behavior of the separated shear layer by introducing the local recirculation. The upstream ribs of sidewall and leeward face ribs, however, show insignificant effect on the flow filed and aerodynamic force. The multi-location combination of ribs generally exhibits better aerodynamic performance than the single-location ribs. The optimal combination can significantly modify the shear layer flow, and reduce the surface pressure, mean drag force and fluctuating lift force. The four-face-ribs arrangement is the most practical arrangement with considering real application. By using this arrangement, the mean drag and fluctuating lift force can be reduced up to 38% and 70%, respectively. The near-façade flow becomes more complicated with more local re-circulations when model is equipped with densely arranged ribs. Correspondingly, the wake vortex is obviously shortened accompanying with increase of wind force. The space in between the ribs is also found to be an essential factor for modifying the flow structure and wind load acting on the structure.

WIND INTERFERENCE ON A HEXAGONAL SHAPED HIGHRISE BUILDINGS WITH DIFFERENT OPENINGS

The wind load and pressure on a tall hexagonal structure altered as the apertures changed in this study. In various conditions, wind angles ranging from 0 to 90 degrees with a 30-degree gap are being used. The distance between the interference building and the model building was gradually raised from 50mm to 200mm at 50mm intervals. At a scale of 1:500, the main building model was studied. The ANSYS CFX package's validity was also tested using a rigid model with dimensions of 100mm x 100mm and a height of 700mm. The k-ε-turbulence model was utilised in the investigation, which was conducted using Computational Fluid Dynamics (CFD) and the ANSYS CFX software package. According to the analysis, changing the percentage of opening area has an influence on building stability because it affects the pressure on the leeward and windward faces. Contours and vortex formation were used to highlight the relationship between different scenarios. As the distance between the interference and model buildings expands, so does the pressure coefficient of the faces. The effects of apertures on the model building were also investigated, with 5-40% openings provided.

WIND INTERFERENCE ON A HEXAGONAL SHAPED HIGHRISE BUILDINGS WITH DIFFERENT OPENINGS

The wind load and pressure on a tall hexagonal structure altered as the apertures changed in this study. In various conditions, wind angles ranging from 0 to 90 degrees with a 30-degree gap are being used. The distance between the interference building and the model building was gradually raised from 50mm to 200mm at 50mm intervals. At a scale of 1:500, the main building model was studied. The ANSYS CFX package's validity was also tested using a rigid model with dimensions of 100mm x 100mm and a height of 700mm. The k-ε-turbulence model was utilised in the investigation, which was conducted using Computational Fluid Dynamics (CFD) and the ANSYS CFX software package. According to the analysis, changing the percentage of opening area has an influence on building stability because it affects the pressure on the leeward and windward faces. Contours and vortex formation were used to highlight the relationship between different scenarios. As the distance between the interference and model buildings expands, so does the pressure coefficient of the faces. The effects of apertures on the model building were also investigated, with 5-40% openings provided.

Analysis of the wind flow and fire spread dynamics over a sloped–ridgeline hill

This paper presents results from a computational and laboratory investigation of wind flow and fire spread over an isolated sloped-ridgeline laboratory-scale hill under various slopes with the wind blowing perpendicularly to the ridgeline. The results show two situations of unexpected or unusual fire behaviour; one is a lateral spread of the fire front over the windward face into a down-ridge direction resulting from a strong near-surface flow component parallel to the ridgeline. The other behaviour is a lateral enlargement of the fire front near the ridgeline over the leeward face in an up-ridge direction resulting from a flow parallel to the ridgeline. Comparison with reference fire spread rates and wind flow observations highlight the importance of the interaction between terrain-modified flow mechanisms and the fire in which they result in accelerated flows that drive the indicated unexpected behaviour.

Experimental investigations of interference effects on wind pressures of tall buildings

The interference effects between two tall buildings on building surface wind pressures are studied by using wind tunnel experiments. Different breadth ratios ( B r = B interfering/ Bprincipal), depth ratios ( D r = D interfering/ Dprincipal), and relative locations of the two buildings are tested. The results show that the interference effects on mean wind pressures on the windward face and the right face are more considerable than those on the other two faces. The windward face mainly shows the shielding effect, while the right face exhibits the amplification effect. The surface interference factors ( SIF) of windward and right faces under different breadth ratios and depth ratios have clear correlation with the reference values ( B r = D r = 1.0), and a series of correlation formulas are obtained. The SIF values of the windward face in tandem arrangement and the maximum and minimum interference factors of the right face in parallel arrangement are formulated. The most prominent local peak pressure under different cases mainly concentrates in the side edge and upper edge of the windward face, the left upper corner, left lower corner, and the upper-middle part of the right face.

Proximity effects between two plus-plan shaped high-rise buildings on mean and RMS pressure coefficients

Wind-induced interference effects may result in a significant increase or decrease in the wind loads on the buildings constructed in groups due to modifying wind flow around, depending on the shape and relative location of the buildings. Experimental study of wind-induced interference effects on mean and root mean square (RMS) pressure coefficients between two tall buildings are investigated in detail for various interference conditions in this study. The Interference effects on mean and RMS pressure coefficients are presented as interference factors i.e. mean interference factor (MIF) and RMS interference factor (RIF). Results show that the interference effects on local wind pressure are significantly higher on the windward side's faces near the recessed corner. The full blockage condition generates suction on walls facing the gap. The half blockage and no blockage conditions create a more severe interference effect than the full blockage. The maximum value of MIF is 4, 9 and 13 in full, half and no blockage condition, respectively. Interference effects result in reduced wind load on side faces and faces at the leeward side. Suction at side faces reduced approximately by 65% in full blockage condition. RIF’s values less than unity are observed for all interference cases.

Multipoint Synchronous Monitoring of Cladding Pressures on a 600-m-High Skyscraper during Super Typhoon Mangkhut 2018

This paper analyzes the wind pressures on the claddings of a 600-m-high skyscraper in Shenzhen, China, during Super Typhoon Mangkhut on September 16, 2018. A synchronous monitoring system that included 48 pressure transducers was implemented to measure the cladding pressures of the skyscraper during the typhoon event. Based on field measurements, the mean, root-mean-square fluctuating, peak (maximum and minimum) pressure coefficients are presented and discussed. Then the mean and peak pressure coefficients are used to validate the design values stipulated in the design code of China. Comparative study finds that the design values of the peak pressure coefficients on the windward and leeward faces of the skyscraper are conservative, while those on the side faces are nonconservative. As for the mean pressure coefficients, the design values are conservative for all faces. Moreover, the non-Gaussian characteristics, power spectral densities, coherences, and correlations of the measured cladding pressures are analyzed to explore the mechanisms of pressure fluctuations on the four sides of the skyscraper. This paper aims to enhance understanding of cladding pressures of high-rise buildings under extreme wind conditions and, therefore, to provide useful information for future designs of wind-resistant skyscrapers in tropical cyclone–prone regions.

Deposition Characteristics of Firebrands on and Around Rectangular Cubic Structures

The focus of the present work is on the deposition of firebrands in a flow over a rectangular cubic block representative of a structure in wildland-urban interface (WUI). The study was carried out by physics based modeling where the wind flow turbulence was dealt with by large eddy simulation (LES) and firebrands were treated by Lagrangian tracking. The Lagrangian equations coupled with the flow solver, accounted for both translational and rotational motions as well as thermochemical degradation of firebrands, assumed to be cylindrical. The dimensions of the structure were varied from 3 to 9 m in the simulations for a parametric study. The simulations were carried out by tracking many firebrands randomly released with a uniform distribution from a horizontal plane 35 m above the ground into the computational domain. The coordinates of the deposited firebrands were used to calculate their normalized number density (number of landed firebrands per unit surface area) to quantify their deposition pattern. On the leewardside of the block, an area, referred to as the safe zone, was identified right behind the structure where firebrands never deposit. The size of the safe zone in the direction perpendicular to the wind was nearly identical to the width of the structure. The length of the safe zone in the wind direction was proportional to the height of the structure. The leeward face of the blocks was never hit by a firebrand. The windward face was hit by many more firebrands than the lateral faces but much less than the top face. The distribution of the number density of the deposited firebrands on the top face was found to be correlated with the flow separation and reattachment on this face.

Direct numerical simulation of turbulent heat transfer in a square duct with transverse ribs mounted on one wall

Turbulent heat transfer in a ribbed square duct of three different blockage ratios are investigated using direct numerical simulation (DNS). The results of ribbed duct cases are compared with those of a heated smooth duct flow. It is observed that owing to the existence of the ribs and confinement of the duct, organized secondary flows appear as large streamwise-elongated vortices, which intensely interact with the rib elements and four sidewalls and have profound influences on the transport of momentum and thermal energy. This study also shows that the drag and heat transfer coefficients are highly sensitive to the rib height. It is observed that as the rib height increases, the impinging effect of the flow on the windward face of the rib strengthens, leading to enhanced rates of turbulent mixing and heat transfer. The influence of sidewalls and rib height on the turbulence structures associated with temperature fluctuations are analyzed based on multiple tools such as vortex swirling strengths, temporal auto-correlations, spatial two-point cross-correlations, joint probability density functions (JPDF) between the temperature and velocity fluctuations, statistical moments of different orders, and temperature spectra.

Flow around surface-mounted permeable cubes on solid and deformable surfaces

A wind tunnel experiment was carried out to characterize the flow surrounding rectangular prisms of varying permeability, each set mounted on a stationary plane-bed surface and subsequently on an erodible bed. Laser-Doppler anemometer measurements of the horizontal and vertical velocity components were obtained in a grid that included an area adjacent to the windward face, enveloped the free end of the form, and extended ≈6.5 element heights downwind of the rear wall. From these component measurements, the total velocity (Tuw), turbulence intensity (TI), Reynold Stress (RS) and the turbulence kinetic energy (TKE) were calculated throughout the sampling array. As compared to an impermeable same-sized cube, the near-surface TKE and RS were substantially reduced within the wake flow behind the permeable elements. In the plane-bed experiments, TI generally increased downwind of the permeable cubes, opposite to the trend for the impermeable form. The distinction in TI was less pronounced, however, when the bed morphology developed scour marks. The impermeable cube had the largest amount of erosion relative to its volume, in response to strong downwash along its windward face and the development of an energetic horseshoe vortex. This coherent flow structure was not detected for all permeable forms and the amount of scour was orders of magnitude less. This study would suggest that for restricting erosion, the efficiency of a surface-mounted element can be improved by making the walls of the form permeable rather than solid, thereby increasing energy dissipation in the wake flow while reducing vortex impingement and bed shear stress.

Air flow and scour patterns around erosion control elements

Abstract A series of wind tunnel experiments was carried out using isolated, surface-mounted elements of varied idealized geometric form to evaluate the relative efficacy of these in wind erosion control. The topography of the bed surface was scanned in high resolution, before and after each wind erosion event, giving the net volume change. The perturbed airflow structure was sampled via laser Doppler anemometry. The volume of erosion initiated by the flow perturbation relative to that of the roughness element was greatest for a rectangular prism in either orientation (face-on 2.5; edge-on 4.0), minimal for a hemisphere (0.2), and below detection for a reference (streamlined) form. Roughness elements that trigger strong downwelling in the perturbed flow and vortex impingement on the bed surface appear to initiate particle motion. Consequently, they are less desirable for wind erosion control, even though they usually have large form drag and demonstrate substantial kinetic energy (KE) dissipation in the wake flow. Hemispheres, with generalized upwelling along both the windward and leeward faces and strong turbulent KE dissipation associated with flow separation along the sidewalls, may present an optimal solution with minimal bed scour.

On aerodynamic droplet breakup

Abstract

Dynamic simulation on high-temperature corrosion behaviour of tube surface with fouling in utility boiler fired by high-chlorine coal

A dynamic model on high-temperature corrosion with fouling-type ash deposition was established to predict the thickness distribution of corrosion layer and the outer/inner layer of ash deposit. It provides an observation on variation of heat transfer characteristics of the alloy test probe over time. This model involves the combustion characteristics of high-chlorine coal, the process of formation, migration, and deposition of fly ash particles, and the corrosion of alloy test probe. In this study, the dynamic model has been integrated into the numerical simulation of high-chlorine coal combustion in a 50 kW long-period corrosion test furnace. The prediction results show that the amount of fly ash deposition on the windward surface is the most while the least amount appears on the side surface. There is a great correlation between the corrosion layer and the inner layer of ash deposit. Because the inner layer of ash deposit and the alloy substrate are spatially adjacent, the high temperature corrosion process is greatly affected by the growth and property of fly ash deposit layer. The simulation results show that the heat flux of probe surface beneath ash deposit is 2.5 kW/m2 which is 50% of the clean surface (5 kW/m2). The changing pattern of thermal resistance versus time at different positions of the alloy surface is consistent with the variation of thickness of the corrosion layer and ash deposit layer. The windward face has the highest thermal resistance and the least heat flux due to the highest thickness of the corrosion layer and ash deposit layer. With the increase of probe wall temperature, the ratio of thermal resistance of corrosion layer to total heat transfer resistance increases, and the ratio at the side face is larger than that at other locations. And the proportion of the corrosion layer in thermal resistance for alloy TP347H reaches 8% at the probe wall temperature of 973 K.

Flow around Surface-Mounted Permeable Cubes on Solid Surfaces

A wind tunnel experiment was administered to characterize the flow surrounding rectangular prisms of varying permeability, each set mounted on a stationary plane-bed surface and subsequently on an erodible bed. Laser-Doppler anemometer measurements of the horizontal and vertical velocity components were obtained during a grid that included a neighbourhood adjacent to the windward face, enveloped the free end of the shape, and extended ≈6.5 element heights downwind of the rear wall. From these component measurements, the entire velocity (Tuw), turbulence intensity (TI), Reynold Stress (RS) and therefore the turbulence K.E. (TKE) were calculated throughout the sampling array. As compared to an impermeable same-sized cube, the near-surface TKE and RS were substantially reduced within the wake flow behind the permeable elements. Within the plane-bed experiments, TI generally increased downwind of the permeable cubes, opposite to the trend for the impermeable form. The excellence in TI was less pronounced, however, when the bed morphology developed scour marks. The impermeable cube had the most important amount of abrasion relative to its volume, in response to strong downwash along its windward face and therefore the development of an active horseshoe vortex. This coherent flow structure wasn't detected for all permeable forms and therefore the amount of scour was orders of magnitude less. This study would suggest that for restricting erosion, the efficiency of a surface-mounted element are often improved by making the walls of the shape permeable instead of solid, thereby increasing energy dissipation within the wake flow while reducing vortex impingement and bed shear stress. The study of the flow around surface-mounted, sharp-edged obstacles placed in a channel is fundamental to the understanding of the flow mechanisms for complex two- and three dimensional geometries. There exists a considerable amount of published data for flows over two-dimensional geometries such as ribs and fences. However, there are markedly fewer studies in the literature concerned with the flow around three dimensional obstacles. Of these, most are limited to the study of a single parameter, for example, the reattachment length. It is therefore the aim of this study to provide a general description of the flow around three-dimensional obstacles. Based on the flow visualization experiments performed for obstacles of different aspect ratio (width-to-height), the changes in the flow patterns as a function of aspect ratio are discussed qualitatively. Additionally, large-scale parameters such as the reattachment and separation lengths are discussed quantitatively. The flow around single, surface-mounted, prismatic obstacles submerged in a boundary layer at high Reynolds numbers depends on a large number of parameters.

Roof slope effects on the aerodynamic characteristics of tall buildings

Roof shape of a building placed in a wind flow has particularly significant effects on this flow, in its wake, immediately at the vicinity and far from the structure. This influence is given by an experimental study, undertaken on rectangular models of reduced scale skyscrapers (1:1000), in a subsonic wind tunnel that enabled us to measure the exerted force by wind flow on windward face of the buildings, as well as the pressure distribution according to the longitudinal and the transverse building directions. The drag force acting on the models windward face is very affected by the building slope roof; these results are available for a normal and inclined wind direction. A numerical simulation is carried out to reproduce complex flow developed around the different building models, using Fluent software. We obtain the parietal pressure distribution on the various building faces and we compare the numerical values to the experimental data obtained in the wind tunnel, both are in good agreement with those provided by the international ASCE code. The numerical simulation indicates that complex structure vortices are developed at the buildings wake and allows us a better understanding of the flow phenomena. Analysis of the numerical results reveals a distinct evolution of pressure and velocity fields, the induced downstream flow is particularly complex. The presence of a roof deforms swirling zones: the zone of recirculation in buildings wake is stretched and the flow diagram is modified, which has direct effects on the measured wind force and the pressure distribution.