Impact, absorption and evaporation of raindrops on building facades

In this paper, the impact, absorption and evaporation of raindrops on building facades is investigated by experimental and numerical means. Laboratory experiments were carried out to study the impact of water drops with different diameters, impact speeds and impact angles on a porous building material surface (ceramic brick). The measurements showed that large drops with high impact speeds splash, and that drops with high impact speeds and small impact angles bounce. The measurements, furthermore, allowed measuring the maximum spreading length and width of the drops as a function of drop diameter, impact speed and impact angle. Then, a numerical analysis was performed to study the distribution of impact speed and angle for raindrops hitting the facade of a 4×4×10 m3 tower building. The results demonstrated typical and important tendencies of impact angle and speed across the facade. Finally, the experimental and numerical data were used in a more precise three-dimensional simulation of impact, absorption and evaporation of random and discrete wind-driven raindrops. This was compared with the common one-dimensional simulation of absorption and evaporation at the facade considering a continuous uniform rain load as boundary condition, and significant differences between the two approaches were observed.