Leeward Face 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.

Simultaneous measurement of the distributed longitudinal strain and velocity field for a cantilevered cylinder exposed to turbulent cross flow

The structural response of a cantilevered cylinder under free-stream conditions both with low and high turbulence intensity generated by turbulence-generating grids is analysed with concurrent measurements of the velocity field and the distributed strain. The thin-walled cylinder, with a diameter (D) of 50 mm, is mounted in a water flume as a cantilevered beam supported at one end, with 95% of its body submerged and exposed to cross flow yielding a Reynolds number of Re = 25000. We employ a novel combination of simultaneous particle image velocimetry and distributed strain measurements using Rayleigh backscattering fibre optic sensors. These sensors are embedded onto the surface of the cylinder to measure the experienced strain (ε\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varepsilon $$\\end{document}) of the structure along its spanwise direction, covering both the windward and leeward faces of the cylinder. The sensors fine spatial resolution allows us to discern the influence of the flow on the structural response of the cylinder in two distinct regions of the structure: upstream and downstream of the mean separation location. This differentiation allows us to isolate the local effects introduced by the free-stream conditions on the loading events over the body from the global force generated by the vortex shedding and other coherent motions present within the flow. Distinguishing between these direct and indirect effects helps determine which is more relevant for fatigue-life cycle analysis. The cross power spectral density between the fluctuating velocity field and the strain reveals that the load is dominated by the vortex shedding, and this relationship is intensified with the introduction of free-stream turbulence. It also helps to discern the different dynamics imposed by the two free-stream turbulence conditions.

Vortex core regions of nebkhas and their implications on shadow dune formation

Shadow dunes develop at the lee side of obstacles and are scale-dependent on the obstacle size. However, our recent field investigations showed that the lengths of shadow dunes are not always proportional to the size of obstacles. In this work, field investigations and computational fluid dynamics (CFD) simulations were conducted to study the effects of the scale and vortex of nebkhas on shadow dune development. Results show that although the shadow dune lengths are proportionate to the width (W) and height (H) of nebkhas, the increment rate decreased massively when the W and H of nebkhas are larger than 6 and 2 m, respectively. The CFD simulations suggest that the vortex core regions of the paired symmetrical reversing flow gradually move to the upwind region as the aspect ratio (H/W) of the nebkhas decreases. The size of the paired symmetrical reversing flows is reduced, and the merging of the reversing flows is prevented, potentially entraining the sediments far from the wake region. The sediments could rotate and deposit on both sides of the leeward face of the nebkhas and therefore contribute to the occurrence of short, tongue-like shadow dunes, which are particularly notable when H/W < 1. The vortex core region always occurs at the foot of the lee side of nebkhas with the same H/W regardless of the scale of the nebkhas or the incident wind speed.

Predicting Wildfire Ember Hot-Spots on Gable Roofs via Deep Learning

Ember accumulation on and around homes can lead to spot fires and home ignition. Post wildland fire assessments suggest that this mechanism is one of the leading causes of home destruction in wildland urban interface (WUI) fires. However, the process of ember deposition and accumulation on and around houses remains poorly understood. Herein, we develop a deep learning (DL) model to analyze data from a series of ember-related wind tunnel experiments for a range of wind conditions and roof slopes. The developed model is designed to identify building roof regions where embers will remain in contact with the rooftop. Our results show that the DL model is capable of accurately predicting the position and fraction of the roof on which embers remain in place as a function of the wind speed, wind direction, roof slope, and location on the windward and leeward faces of the rooftop. The DL model was augmented with explainable AI (XAI) measures to examine the extent of the influence of these parameters on the rooftop ember coverage and potential ignition.

Wind Effects on Re-Entrant Wing Faces of Plus Plan-Shaped Building

The wind flow patterns and pressure distribution around a plus-shaped building are significantly influenced by re-entrant corner dimensions and building height. The present study aims to find the wind effects and study the pressure distribution with different flow patterns. The building has a plan area of approximately 300 square meters and a height of 50 m, maintaining equal lengths for the re-entrant corners. The research study is performed using the ANSYS CFX academic version. The study employs diverse visualizations, featuring the pressure coefficient (CPe), vertical and specific surface streamlines, and pressure contours. Wind incidence angles for the study are varied from 0° to 90° at an interval of 15°. Building dimensions are scaled down as per the ASCE wind tunnel test manual, and the length scale is kept at 1:100 for CFD investigation. This approach yields crucial insights into the circulation of wind patterns and the distribution of pressure across a wide range of wind incidence angles. The influence of streamlines in the bottom portion of the building model is relatively minimal. In contrast to the upper portion, the bottom exhibits robust vortices, particularly for the wind angles varying from 0° to 30°. Positive pressure is observed on the windward face, and the leeward face and side face exhibit negative pressure. This study furnishes valuable insights into flow patterns and pressure distribution across a wide range of wind incidence angles from 0° to 90° at an interval of 15°. These findings contribute significantly to a thorough comprehension of the wind flow patterns and pressure distribution around the plus-shaped building model.

Pore-scale hydrodynamics of non-Newtonian power-law fluids across a partially blocked porous medium in a confined channel

Transport of non-Newtonian fluids in porous media is pervasive in many natural and industrial applications. However, capturing the rheological behaviors of fluids by direct experimental techniques is challenging at the pore-scale. This paper outlines the pore-scale hydrodynamic interactions of non-Newtonian power-law fluids across a partially blocked porous medium in the laminar flow regime by computational fluid dynamics. The porous medium consists of an array of uniformly arranged square pillars. We explore the complex interplay of power-law rheology and Reynolds number on the microscopic flow field at the pore-scale. We capture the momentum transfer at the permeable interface between the porous and non-porous regions through stream-wise and span-wise velocity components and average volumetric flow rates at each pore-throat. Our results unveil a significant augmentation in stream-wise momentum by shear-thinning behavior and a diminution in momentum by shear-thickening behavior of the fluid through the porous medium. Further, the flow-leakage at the top interface purely depends on the combined effects of Reynolds number and power-law index. The channel pressure drop between the windward and leeward faces of the porous medium increases with the power-law index at low Reynolds number, while it decreases at high Reynolds number. Moreover, we provide a simple numerical framework to comprehend how the power-law behavior of the fluid dynamically regulates the flow field at the pore-scale.

Evaluating the impact of wind effects on tall buildings with various plan shapes

Tall building is playing important role in the growth of urbanization and has resulted in developing to the vertical rise of the structure. The data available for the designing of the tall building is not sufficient or need some modification up to very limited extent in the present scenario. In this study a rectangular shape having L: B ratio as 1.15 and octagonal plan shape are selected to investigate the wind loads on building. The area of both models is nearly equal for the comparison of the results. Pressure effects are the main concern of considered building model. When it comes to predicting wind-related events on buildings or other structures, computational fluid dynamics (CFD) is a reliable and quicker option. CFD analysis is carried out using a software program called (ANSYS-CFX). This paper presents pressure contours that are calculated at the front, back & adjacent sides of the individual tall buildings. The results clearly show that based upon the building shape, the pressures generated can be either positive pressure or negative which can be either beneficial or can have adverse effects. The result on both the building model shows that the pressure on wind ward face is more or less the same and it does not depend on the shape of the building. In the case of a symmetrical building, the leeward face will always be subjected to the suction effect, while the side faces will always exhibit an equal pressure distribution.

Firebrand deposition on cubic structures in tandem and parallel arrangements

Spot fires created by wind–carrying firebrands are common in wildland–urban interface (WUI) fires. Firebrand deposition over cubic blocks in tandem and parallel arrangements representing simplified nearby small structures in WUI was studied. The flow turbulence was modeled by large eddy simulation, and the firebrands were simulated in the Lagrangian framework. Both translational and rotational motions, and the thermal degradation of firebrands were accounted for. Various separation distances between blocks and wind speeds were considered. Simulations revealed that the blocks shielded their immediate leeward areas on the ground from firebrand deposition. These areas were distinguished by having no deposited firebrands, and were hence called safe zones, which were nearly in the shape of an isosceles trapezoid. The longer base of the trapezoid coincided with the bottom edge of the block’s leeward face, and the shorter base and the legs of the trapezoid constituted the borderlines of the safe zone. The safe zone length (i.e. the trapezoid height) in the wind direction increased with the wind speeds without a significant sensitivity to the block position in either arrangement. For the blocks in the tandem arrangement with a smaller separation distance and/or higher wind speeds, the safe zone encroaches on the windward face of the downwind block. Therefore, an upwind block also shielded the lower part of the windward face of the downwind block from firebrand deposition in these cases. In none of the simulations, firebrands were deposited on the leeward faces. In all simulations, the firebrands deposited on the lateral faces that were parallel to the wind direction were much less than those on the windward faces.

Bistability in the wake of a circular cylinder with passive control using two leeward rods

This paper presents an experimental investigation on the flow around a circular cylinder controlled by a pair of rods placed close to the separated shear layers from the leeward face of the cylinder. Past research of Cicolin et al. (2021) has shown that one control rod, placed at specific positions, induces a late flow separation on the main cylinder’s surface in a typical occurrence of the Coandă effect. As a result the control rod reduced the mean drag acting on the cylinder but also produced a net mean lift force. We now present an extension of the aforementioned study to consideration of a pair of symmetrically arranged control rods, aimed at eliminating the mean lift force whilst maintaining a drag reduction. The experiments were carried out at a Reynolds number Re=20,000 based on the diameter of the main cylinder D, with the diameter of the control rods being ten times smaller than that of the cylinder. The centre-to-centre distances between each control rod and the cylinder was 0.7D, and the angular position of the rods varied from θ=120∘ to 125∘, where θ is measured from the front stagnation point. Time-resolved PIV velocity fields and hydrodynamic forces were measured for the different setups. Results show that the mean flow is asymmetric in spite of the symmetry of the geometric model and position of the rods. The pair of control rods induces a bistable flow, induced by the imbalance of two colliding jets in the near wake. The dynamics were found to be random, with the average switching time between stable states depending on the position of the rods. The mean drag force was reduced by up to 15%, and the mean lift force was reduced by 80% compared to the cases with a single control rod. It was also observed that the control rod can induce two different types of flow separation from the main cylinder, one in which the flow separates from the main cylinder only once and one in which a small separation bubble forms in proximity to the control rod before reattaching and then permanently separating. These distinct features play an important role in the dynamics of the bistability and hint at a possible extension of the total drag reduction to 30% if the bistability is suppressed.

Modeling of heat transfer in a narrow rectangular channel with partial swelling blockage

In plate-fuel-assembly reactor cores, owing to the cladding swelling caused by irradiation damage under high burnup conditions, narrow rectangular channels may be partially blocked. The partial blockage will alter the flow channel shape and affect the heat transfer characteristics. Thus, it is important to focus on the flow and heat transfer characteristics under partial blockage conditions. Accordingly, in this study, the heat transfer at the entrance region of a narrow rectangular channel with protrusions is numerically investigated. Further, variations in the local Nusselt number and fluid field distribution are studied. Results reveal that the protrusions lead to a wake effect that influences the local heat transfer in the blockage region and wake zones. At the upwind face of the protrusions, the local heat transfer increases to a crest value over the hydraulic diameter. A low-speed recirculation region is also formed over a short distance at the intermediate leeward face of the protrusion, resulting in local deterioration of the heat transfer. Moreover, in the wake zone, heat transfer is enhanced owing to the disturbance of the flow streams with different velocities. The effects of the blockage ratio, number, and interval of protrusions on the local heat transfer are also analyzed. This augmentation of the heat transfer decreases with an increase in the Reynolds number, whereas it increases with the height ratio of the protrusions. Additionally, a multiple regression analysis method is employed to analyze the numerical simulation data. Based on these numerical investigations, dimensionless correlations are proposed to estimate the local Nusselt number for rectangular channels with and without partial swelling blockages. The predicted results are in good agreement with the experimental data and reference correlations. For Eqs. (20) and (22), the major points are located within the relative deviation limit of ± 15%, while for Eq. (21), all the data points fall within the relative deviation limit of ± 20%. Comparison results indicate that the correlations can be used to understand the heat transfer upstream and downstream of partial blockages. Furthermore, numerical investigations and qualitative analyses of the effect of spare protrusions on the local heat transfer in the wake area are performed. These spare protrusions lead to local heat transfer deterioration in the wake zone; notably, the spacing between these protrusions does not have a significant influence on the augmentation of the heat transfer downstream.

CFD simulations for evaluating the wind effects on high-rise buildings having varying cross-sectional shape

PurposeIn this study the comparison is presented for the variation in cross-sectional shape along the height of the building model. For this purpose Model B and Model C are having the considerable variation and Model A result can be easily predicted on the basis of the result of Model B and C while Model X is considered for the validation purposes only and it is well established that the results are within the allowable limit. This paper aims to discuss these wind generated effects in the tall building model.Design/methodology/approachComputational Fluid Dynamics (CFD) in ANSYS: CFX is used to investigate the wind effects on varying cross-sectional shape along the height of the building model.FindingsFrom pressure contours, it was observed that shape and size of the face is independent of the pressure distribution. It is also observed that pressure distribution for the windward face (A) was less than the magnitude of the leeward face for both models. The leeward face and lateral faces had similar pressure distribution. Also slight changes in pressure distribution were observed at the periphery of the models.Originality/valueThis study has been performed to analyse and compare the wind effect on tall buildings having varying cross sections with variation of different cross sections along the height. Most of the studies done in the field of tall buildings are concentrated to one particular cross-sectional shape while the present study investigates wind effects for combination of two types of cross sections along the height. This analysis is performed for wind incidence angles ranging from 0° to 90° at an interval of 30°. Analysis of wind flow characteristics of two models, Models B and C will be computed using CFD. These two models are the variation of Model A which is a combination of two types of cross section that is square and plus. Square and plus cross-sectional heights for Model B are 48 m and 144 m, respectively. Similarly, square and plus cross-sectional heights for Model C are 144 m and 48 m, respectively. The results are interpreted using pressure contours and streamlines, and comparative graphs of drag and lift forces are presented.

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.

Influence of Refined Wind Load Parameters and Wind-Loading Mode on Wind-Induced Responses of a Long Cross-Arm Angle-Steel Transmission Tower

This study aims to investigate refined wind load parameters on main rods and the influence of wind-loading mode on wind-induced responses of the angle-steel transmission tower. The wind load parameters discussed in this study include drag coefficients, wind load distribution factors and skewed wind load factors. To achieve the aim, wind tunnel tests were conducted to explore aerodynamic loads for integrated frame, single frame, and main rod models of cross-arm and tower body. The wind load parameters of the different models were investigated. In addition, a series of wind-induced vibration simulation was applied to examine the wind-induced responses of an ultra-high voltage (UHV) transmission tower with a long cross-arm under concentrated and distributed wind loads. The simulated results under the two types of wind loads were compared. The results show that the longitudinal drag coefficients of the main rods are smaller than the values of the integrated frame, and equivalent on average to the values of the single frame. The experimental shielding factor of the cross-arm is larger than those in different standards due to the joint drag effects of leeward, upper, and lower faces of the cross-arm in the wind tunnel test. The experimented shielding factor of the tower body is in line with those referring to the Chinese and AS/NZS standards, and slightly larger than those based on the British and JEC standards. The skewed wind load factors of the main rod models are quite different from other models for cross-arm and tower body. The wind-induced vibration simulation suggests that, the wind-loading mode has limited impact on the displacements, accelerations, and gust factors of the transmission tower, but significantly influences the maximum normal stresses (MNSs) of the rods’ cross-sections. The MNSs caused by the distributed wind loads are obviously greater than those caused by concentrated wind loads, especially for the rods at the two ends of the cross-arm.

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.

Numerical Study of Wind Loads on Y Plan-Shaped Tall Building Using CFD

The increase in the population is at an exponential rate, and the available land is in the form of irregular shapes. That is why irregular shapes are very commonly built. Wind load increases with respect to height, so wind load evolution is necessary for such high-rise structures. Wind forces majorly depend on the plan's cross-sectional shape. Therefore, for an irregular shape, an investigation is needed for tall buildings. This paper demonstrates a detailed study on velocity stream line, external pressure coefficients, pressure distribution on the surfaces of the building and the turbulence kinetic energy for the Y-shaped plan for tall buildings under wind excitation for wind incidence angles of 0o to 180o. k- turbulence model is utilized to solve the problem using computational fluid dynamics techniques in ANSYS for terrain category II as per IS: 875 (Part3), 2015. Wind ward faces in all building models show positive pressure distribution, while the leeward faces are under the effect of negative pressure distribution. Wind load can be reduced on building models by modifying the corners, such as chamfering, rounding, and double recessed. The variation of pressure distribution on different faces of a "Y" plan shaped tall building for 0° and 180° is investigated using ANSYS CFX, and the pressure contours are plotted for all the faces of different "Y" shaped buildings to compute the effect of corner modification on pressure distribution. In this research, it was found that building models with rounded corners are highly efficient in resisting the wind load. Doi: 10.28991/CEJ-2022-08-02-06 Full Text: PDF

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.

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.