Wind, rain and the building envelope: studies at the Laboratory of Building Physics, KULeuven

Driving rain is one of the most important moisture sources affecting building envelopes. Until recently, information on driving rain was gathered by employing either an experimental or a semi-empirical approach. As research efforts continued to reveal the inherent complexity of the problem, researchers realized that further achievements were to be found through numerical analyses. In the past decade, Computational Fluid Dynamics (CFD) has made its introduction in the area. Choi (1993; 1994a; 1994b) developed a numerical simulation technique to determine the distribution of driving rain on buildings under steady-state conditions of wind and rain. A numerical method for estimating transient driving rain loads was introduced by Blocken and Carmeliet (2000a; 2000b). Van Mook (1999) and Hangan (1999) provided a first experimental verification of the steady-state simulation technique. Verification efforts for the transient numerical method are reported in Blocken and Carmeliet (2000a; 2002). The current paper is an attempt to illustrate the practical use of the numerical method and to give some further insight in the interaction between wind, rain and the building envelope. First, the catch ratio as a measure for the amount of driving rain falling on building facades is defined. Next, the transient numerical method is briefly outlined. Finally, two case studies that were recently conducted at the Laboratory of Building Physics are described.