Parameters affecting the intensity of wind-driven rain on the front face of a building

Abstract

In the weathertightness design of building envelope, it is important to know the amount of rain water impinging on the faces of a building. Wind-driven rain around buildings is a complex phenomenon, and the intensity of wind-driven rain on a building face is affected by many parameters. The characteristics of the approaching wind and rain are important parameters. The interactions between wind, rain and the building are also expected to have strong effect on the wind-driven rain intensity. This paper identifies the parameters affecting the intensity of wind-driven rain impinging onto the front face of a building and investigates how the intensity is affected. It examines each phase of the process and their governing parameters which can be grouped into the following areas. They are (a) rainfall characteristics (drop size distribution, intensity), (b) wind speed, (c) building geometry and (d) statistics of the co-ocurrence of wind and rain. A computational fluid dynamics model is set up and the wind flow pattern around a building, the raindrop trajectories and the wind-driven rain intensity on the front face of a building are calculated. This model is used for the evaluation of the effects on the wind-driven rain intensity due to the various parameters. The findings indicated that while wind speed, rainfall intensity and building geometry all play a part in effecting the wind-driven rain intensity, the design intensity is governed by the statistics of the co-occurrence of wind and rain.