On the impact of roof geometry on rain shelter in football stadia

Apart from sports purposes, stadia are also increasingly being used for concerts and other events with large spectator attendance. The main aspect for spectator comfort in open stadia is protection from wind and rain. In the design of many existing stadia, however, rain shelter has insufficiently been taken into account, because most roofs have been designed with vertical rainfall in mind, while no consideration has been given to the possibility of rain being blown onto the stands and spectators by wind (wind-driven rain). Adequate rain shelter should be addressed during the design stage of new sports and football stadia. Currently, almost no information or guidelines on this matter are available. This paper presents an investigation of the impact of roof geometry on rain shelter for stadia that consist of two separate roof-covered stands facing each other. 2D Computational Fluid Dynamics (CFD) simulations and Lagrangian particle tracking are performed to analyze the wind-flow pattern and rainfall distribution for seven generic stadium cross-section configurations and to assess the performance of each roof type. Although most existing stadium roofs are built with a light to medium upward slope towards the field, the analysis indicates that roofs with a downward slope of 13° provide significantly better rain shelter. The reason is not only the well-known trigonometric shielding effect. In addition, this roof type—as opposed to its counterparts—seems to restrict the extent of the primary vortex in the stadium and appears to generate a sufficiently strong counter-rotating secondary vortex below the roof that sweeps the rain away from the stands.