Wind-driven rain (WDR) is one of the most important moisture sources with potential negative effects on hygrothermal performance and durability of buildings. The impact of WDR on building facades can be understood in a better way by predicting the surface wetting distribution accurately. Computational Fluid Dynamics (CFD) simulation with the Lagrangian particle tracking (LPT) method has been widely used and validated by several researchers for different isolated building configurations. In this paper, Eulerian Multiphase modeling (EM) for WDR assessment is applied and validated for a monumental tower building (St. Hubertus building in The Netherlands). The LPT and EM models show comparable results and EM is validated by comparison of the calculated catch ratio values with available experimental data on windward facade. The deviations between the experimental and the model results at low rain intensity and wind speed are attributed to the absence of turbulent dispersion in both LPT and EM models. EM has the advantages, first, of less computational complexity and faster pre-processing and post-processing in terms of raindrop trajectories and WDR catch ratios, and second, of allowing the calculation of catch ratios on all surfaces of a complex geometry over the domain at once. The user time spent for the simulation decreases by at least a factor of 10 using EM instead of LPT for a single building. Additionally, the EM is expected to provide a sound basis for future WDR studies incorporating more accurate calculation of the wind flow field, e.g. by LES and the inclusion of turbulent dispersion.

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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.

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Building materials play an important role in the absorption, transport and storage of heat and moisture in the built environment. A fully-integrated urban microclimate model is proposed, which solves for wind flow and for the transport of heat and moisture in the air and building materials. The model includes long-wave and shortwave radiative exchange between surfaces and the distribution of wind-driven rain intensity. Transport in air and building materials are coupled in such a way that the steady Reynolds-averaged Navier-Stokes (RANS) is solved iteratively with the unsteady heat and moisture transfer in building materials. The proposed approach provides the information required for analyzing different contributions of convective cooling, sensible heat transfer due to rain, evaporation, in addition to the thermal storage throughout the day. This approach is demonstrated with a case study investigating the impact of rain deposition on an isolated three-dimensional street canyon lined with porous building materials. The study shows different rate of evaporation and duration of evaporative cooling for a change in wind speed during a rain event. The distribution of wind-driven rain particularly influences the spatial and temporal distribution of surface and air temperatures. A significant influence of neighboring surfaces is found on the surface temperatures.

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 facades can be understood in a better way by predicting the surface wetting distribution accurately. Computational Fluid Dynamics (CFD) simulations can be used to obtain accurate spatial and temporal information on WDR. In many previous numerical WDR studies, the turbulent dispersion of the raindrops has been neglected. However, it is not clear to what extent this assumption is justified, and to what extent the deviations between the experimental and the numerical results in previous studies can be attributed to the absence of turbulent dispersion in the model. In this paper, an implementation of turbulent dispersion into an Eulerian Multiphase (EM) model for WDR assessment is proposed. First, CFD WDR simulations are performed for a simplified isolated high-rise building, with and without turbulent dispersion. It is shown that the turbulence intensity field in the vicinity of the building, and correspondingly the turbulence kinetic energy field, has a strong influence on the estimated catch ratio values when turbulent dispersion is taken into account. Next, CFD WDR simulations are made for a monumental tower building, for which experimental data are available. It is shown that taking turbulent dispersion into account reduces the average deviation between simulations and measurements from 24% to 15%.

Most studies of wind-driven rain (WDR) reported in the literature focus either on isolated buildings or on a particular building in geometrically complex environments. There is a need for experimental and numerical studies for more generic multi-building geometries. The present study reports detailed field measurements and numerical simulations of WDR that are conducted for an idealized geometry with two parallel wide buildings with different heights, located in Dübendorf, Switzerland. The datasets of rain events and WDR measurements with high spatial and temporal resolution are made available online to download and are intended for model development and validation. Numerical simulations are performed with computational fluid dynamics (CFD) based on the 3D steady Reynolds-averaged Navier-Stokes (RANS) equations and an Eulerian multiphase (EM) model for WDR, including the turbulent dispersion of raindrops. The numerical results are validated by comparing the calculated catch ratio values and cumulative WDR amounts with data from the field measurements. The CFD simulations accurately estimate the WDR intensities at the positions of 18 WDR gauges. The average discrepancies between the numerical and experimental results are found to be 6.9% for the rain event on February 20-21, 2014 and 4.9% for the rain event on August 2-3, 2014. In different building configurations, the influences of recirculation regions, sheltering, wind-blocking effect and acceleration of wind determine the WDR distribution on the downstream building. WDR can increase due to recirculation regions and acceleration of wind, while wind-blocking effect and sheltering decrease WDR.

An urban microclimate model is used to design a smart wetting protocol for multilayer street pavements in order to maximize the evaporative cooling effect as a mitigation measure for thermal discomfort during heat waves. The microclimate model is built upon a computational fluid dynamics (CFD) model for solving the turbulent air, heat and moisture flow in the air domain of a street canyon. The CFD model is coupled to a model for heat and moisture transport in porous urban materials and to a radiative exchange model, determining the net solar and thermal radiation on each urban surface. A two-layer pavement system, previously optimized for maximal evaporative cooling applying the principles of capillary pumping and capillary break, is considered to design a smart wetting protocol answering the questions “when,” “how much,” and “how long” a pavement should be artificially wetted. It was found for the current optimized pavement solutions that a daily amount of 6 mm wetting over 10 min in the morning, preferentially between 8:00 and 10:00, guarantees a maximal evaporative cooling for 24 h during a heat wave.