Wind-driven rain on building facades: Some perspectives

In the past 70 years, considerable advances have been made in wind-driven rain (WDR) research in building engineering. Experimental, semi-empirical and numerical simulation methods have been developed and applied to assess the amount of WDR impinging on building facades. Each of these methods has been combined with hygrothermal simulation models to determine the uptake of WDR water by porous building materials, and these models have become standard evaluation tools for building facade performance and durability. Several state-of-the-art rain penetration testing facilities have been developed and applied. In spite of these achievements, considerable challenges remain. Semi-empirical methods are often not accurate enough to capture the complexity of WDR. Numerical simulation based on Computational Fluid Dynamics (CFD) has hardly been explored beyond the case of the isolated building model. Little is known about the contact and surface phenomena that can occur at raindrop impact. More information is also needed on rain penetration mechanisms. At present, research efforts are focusing on at least these four research tracks. The complexity of WDR ensures they will continue to do so for a considerable time in the future.