CFD simulation and validation of wind-driven rain on a building facade with an Eulerian multiphase model

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