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Accurate estimation of wind-driven rain (WDR) load on building facades is of paramount importance for the assessment of moisture-induced damage risks. The response of the facade depends on the used meteorological data, which can show significant variation over time, especially considering climate change. In this study, a statistical approach based on a Latin Hypercube Sampling (LHS) is used to generate reduced samples, which accurately represent long-term meteorological conditions for WDR. Based on cumulative distribution functions, the generated samples with LHS are a subset of actual measured data, independent of the temporal information, and are clustered around values of highest frequency. Computational fluid dynamics (CFD) simulations of WDR are performed on a historical building located in Victoria, BC, Canada based on a previously validated methodology, determining the parts of facade receiving the highest WDR load. The sensitivity study shows that a sample size of 200 with LHS, corresponding to around 0.2% of the total measured data and 4.1% of the data during rainfall, is sufficient to replicate successfully the spatial distribution of WDR with a maximum discrepancy of 7%. The reduced samples can be easily modified to model various scenarios with respect to the climate change. The change in WDR load is presented for different scenarios in terms of rainfall intensity and wind speed as predicted by future climatic conditions. The results indicate that the future WDR load depends highly on the wind speed conditions, even when wind speed is kept constant and only rainfall intensity is varied. • Long-term representative data are generated with Latin Hypercube Sampling. • The generated reduced samples successfully replicate wind-driven rain load. • 4% of measured rain data is enough to replicate wind rose and driving-rain index. • Largest impact on future wind-driven rain load is when the wind velocity changes. • Change in catch ratio at increased future rainfall intensity depends on wind speed. [ABSTRACT FROM AUTHOR]

Abstract: Wind-driven rain (WDR) is one of the most important moisture sources with potential negative effects on the hygrothermal performance and durability of building facades. The impact of WDR on building envelopes can be understood in a better way when the WDR intensity distribution can be accurately predicted. Most field experiments of WDR reported in the literature focused on either stand-alone buildings or on buildings in geometrically complex environments. There is a need for high-resolution measurements in more generic and idealized multi-building configurations. The present study reports WDR measurements that were conducted with high spatial and temporal resolution in a test setup consisting of an array of 9 low-rise cubic building models, located in Dübendorf, Switzerland. Detailed descriptions are provided of the building models, the surroundings, the measuring instruments, the measurements of WDR, wind speed, wind direction, horizontal rainfall intensity and air temperature during three selected rain events, as well as error estimates for the WDR measurements. The datasets of rain events and WDR measurement results are made available online to download and are intended for WDR model development and validation. [Copyright &y& Elsevier]

Abstract: In the past, different calculation models for wind-driven rain (WDR) have been developed and progressively improved. Today, the models that are most advanced and most frequently used are the semi-empirical model in the ISO Standard for WDR (ISO), the semi-empirical model by Straube and Burnett (SB) and the CFD model by Choi, extended by Blocken and Carmeliet. Each of these models is quite different, and to the knowledge of the authors, no comparison of these models has yet been performed. This paper first presents a detailed overview of the three models, including new insights in similarities between these models and relations with recent research results. Based on this overview, it provides a comparison focused on the extent to which the different influencing parameters of WDR are implemented in the models. It shows that the implementation of the influencing parameters is most pronounced for the CFD model, less pronounced for the ISO model and least pronounced for the SB model. It is also shown that in the two semi-empirical models, the values of the wall factor W (for ISO) and the rain admittance function RAF (for SB), which have the same definition in both models, can differ more than a factor 2 from each other. The two models can therefore provide very different results. They also require differently defined reference wind speed values as input. The overview and the comparison in this paper provide the basis for future comparison studies and future improvements of the semi-empirical models. [Copyright &y& Elsevier]

The Venturi effect refers to the increase in fluid speed due to a decrease of the flow section in confined flows. The wind speed conditions in converging and diverging passages between perpendicular buildings are studied with computational fluid dynamics to investigate the extent to which the so-called Venturi effect is present in the passages. Model validation is performed by comparing the numerical results with wind tunnel measurements. The validated model is employed for a detailed investigation of the wind speed and the flow rate in the passages for a wide range of passage widths. The simulations show an increase in wind speed near ground level, but a decrease of horizontal wind speed in the upper part of the converging passages. The reason is the wind-blocking effect, which causes a large part of the oncoming wind to flow over and around the buildings, rather than being forced through the passage. Due to this effect, the flow rates through the converging passages are consistently lower than the free-field flow rate, implying that the term Venturi effect is less applicable for such building configurations. [ABSTRACT FROM AUTHOR]

This paper presents wind tunnel measurements of pedestrian wind conditions in passages between various configurations of two long narrow perpendicular buildings in open country exposure. The investigated parameters are passage width, building height and wind direction. The measurements were made along the passage centerline. The aim of this paper is to provide more insight in the pedestrian wind conditions in these basic building configurations, to address some contradictory statements reported in the literature and to provide detailed experimental data for computational fluid dynamics (CFD) validation. The results show that the wind speed amplification factors in diverging passages are generally larger than in converging passages. It is also shown that the maximum wind speed amplification factors increase monotonically with decreasing passage width, contrary to some general building design guidelines proposed in the past for such building configurations. Significant issues concerning the use of the experimental data for CFD validation are also discussed. [ABSTRACT FROM AUTHOR]

As cities are densified, the presence of high-rise buildings can deteriorate wind-comfort conditions in urban neighborhoods with low-rise buildings. The present study aims to determine critical heights above which the pedestrian wind comfort deteriorates. Wind-flow patterns around high-rise buildings are investigated in different idealized configurations based on a systematic parametric study using computational fluid dynamics (CFD) simulations. The impact of trees around high-rise buildings is quantified as a potential measure to reduce wind speed. As a further step, amplification factors obtained from CFD simulations are combined with available city-wide statistical data to obtain wind-comfort prediction maps. The results show that pedestrian wind comfort can worsen severely with a high-rise building exceeding two times the height of surrounding buildings. Above four times the height, any arrangement of surrounding buildings yields similar conditions in areas in close proximity to the high-rise building. However, the arrangement of buildings defines the overall wind-flow pattern. In staggered arrangement, in case of very tall buildings, critical corner streams are observed around neighboring buildings downstream. Large trees can reduce average wind speed, but they have only limited impact on the accelerated flow around the corners due to downflow from the high-rise building. [Display omitted] • Buildings exceeding twice the height of surroundings worsen pedestrian wind comfort. • Above four times the height, urban morphology has negligible impact on wind comfort. • Very tall high-rise buildings can create critical corner streams in the neighborhood. • Wind-amplification factors are upscaled to obtain city-wide wind comfort maps. • Trees do not weaken corner streams significantly but lower wind speed at street level. [ABSTRACT FROM AUTHOR]

Abstract: We introduce the ventilation potential (VP) as a statistical, climate-dependent measure to assess the removal of scalars, such as heat and pollutants, from courtyards or urban street canyons. The VP is obtained following a three-step approach. First, the magnitude of the flux through a horizontal surface situated at the top of the courtyard or canyon is determined by means of computational fluid dynamics (CFD) simulations for various courtyard geometries and ambient wind directions. Then, this exchange flux is normalized with the free-stream wind speed and subsequently parameterized as a function of the courtyard’s length-to-width ratio and the incidence angle of the wind flow. Finally, the combination of the parameterization with site-specific wind data yields the VP. This study reveals that the normalized exchange flux is maximal when the angle between the prevailing flow direction and the main courtyard axis is about 15–30°, regardless of the courtyard length. The normalized exchange flux increases with increasing courtyard length, and approaches the optimum for courtyards with a length-to-height ratio of ten. Longer courtyards behave as urban street canyons. Unsteady (LES) simulations lead to a much higher VP and thus favor scalar removal when compared with steady (RANS) simulations. These observations can have a decisive impact on urban planning, human comfort and health. [Copyright &y& Elsevier]

Knowledge of the convective heat transfer coefficient (CHTC) for external building surfaces is essential for analysis of building heat gains and losses and hygrothermal analysis of building components. The CHTC is influenced by a wide range of parameters. Previous studies analysed the influence of position on the building facade, roughness, wind speed, wind direction, local airflow pattern and surface-to-air temperature differences. Among methods, Computational Fluid Dynamics (CFD) is a useful tool to determine the distribution of the CHTC across building facades as a function of the governing parameters . However, to the best of our knowledge, research on the influence of building size and geometry on the CHTC is very limited . Therefore this paper presents high-resolution 3D steady Reynolds-averaged Navier-Stokes (RANS) CFD simulations of forced convective heat transfer at the windward facade of 22 buildings of different geometry. First, a CFD validation study focused on CHTC is performed based on wind-tunnel measurements of surface temperature for a reduced-scale wall-mounted cubic obstacle. Next, the influence of building geometry on the CHTC distribution is investigated at different reference wind speeds, U 10 , for three groups: buildings with H ≥ W , buildings with H ≤ W and buildings with H = W . The results show that CHTC / ( U 10 0.84 ) is relatively insensitive to the reference wind speed. For W =10 m and by increasing H from 10 m to 80 m, the surface-averaged CHTC / ( U 10 0.84 ) on the windward facade increases by about 20%. However, for H =10 m, increasing the building width from 10 to 80 m has the opposite impact on the surface-averaged CHTC / ( U 10 0.84 ) , which decreases by more than 33%. For buildings with H = W , it decreases by more than 10% as H and W increase from 10 to 40 m, and remains approximately constant for higher values of H (= W ). The reason for these trends are explained. [ABSTRACT FROM AUTHOR]

Abstract: Wind-driven rain (WDR) deposition on a two-building configuration is studied with Computational Fluid Dynamics (CFD). The configuration consists of a high-rise building screened by a low-rise building. Validation of the wind-flow simulations is performed with Particle Image Velocimetry (PIV) measurements in a wind tunnel. Raindrop motion is simulated by Lagrangian particle tracking in the mean wind-flow pattern with a reference wind speed U 10=10m/s. Horizontal rainfall intensities R h=5 and 30mm/h are considered. Simulations of WDR are performed for the two-building configuration and for each building separately, to analyse the mutual influence of the buildings on their WDR deposition pattern. The simulation results indicate that this influence is very pronounced and that it is to some extent opposite to what might be expected. The low-rise building influences the deposition on the high-rise building (downstream disturbance), not by partly shielding it from wind and WDR, but by increasing the strength of the standing vortex between the two buildings. This locally increases WDR intensities on the high-rise building facade by more than a factor 2 for both R h=5 and 30mm/h. On the other hand, the high-rise building influences deposition on the low-rise building facade (upstream disturbance) by the wind-blocking effect. This effect yields a reduction in WDR deposition on the low-rise building facade by up to about 25% for both R h=5 and 30mm/h. In the European standard draft for WDR assessment, the mutual influence can only be taken into account by a simplified reduction factor, called the obstruction factor. It only considers downstream disturbances, and does not consider the possibility of increased WDR deposition due to neighbouring buildings. Care should therefore be exercised when using the current version of the obstruction factor to determine WDR exposure. [Copyright &y& Elsevier]