New Developments in Understanding Wind-driven Rain Deposition on Building Envelopes and its Consequences

Wind-driven rain (WDR) refers to rain droplets, driven by the wind, impacting on surfaces in the built environment, leading to wetting and dryingprocesses affecting buildings and the urban microclimate. The proper understanding and management of WDR in the built environment as water source isrequired since evaporative cooling from wetted urban surfaces is a future avenue for mitigating urban heat island effects and heat waves, expected toincrease due to climate change. A second reason is that WDR is a main agent of deterioration of building materials and, when climate change leads tomore extreme weather events such as heavy rain, it is expected that building damage risks will increase in the coming decades.The proposed methodology allows a better understanding and modeling of the different physical processes involved in WDR deposition on building. Wehave developed an Eulerian Multiphase CFD model for WDR prediction in complex urban environment. This model was validated with field rainmeasurements on multiple buildings and wind tunnel air flow measurements.Studying rain deposition on facades, modulations such as roof overhang and balconies are shown to be effective at sheltering the facade from WDR, butare themselves exposed to higher amount of WDR compared to a flat façade. As the wind speed increases, the sheltering provided by roof overhang andbalconies decreases as the raindrops move more horizontally. Windows sills are very effective at decreasing catch ratio and droplet impact speed. Contoursof catch ratio on the ground show a high WDR intensity region around the building resembling a horse-shoe shape for wind direction perpendicular to themain façade. The study of driving rain can inform designers and building scientists. For this, we provide a tutorial on starting up with WDR simulationwithin the OpenFOAM environment.