APPRAISAL OF A SEMI-EMPIRICAL MODEL FOR THE PRESSURE FIELD BENEATH ROOF CORNER VORTICES

Abstract

In 1990 Cook described a semi-empirical model for predicting the pressure field beneath roof corner vortices. He proposed that the flow can be considered as a conical vortex “growth region” near the roof corner, and as a cylindrical vortex “mature region” further away from the corner, and derived an equation for surface pressure based on the supposed mechanics of a Rankine vortex with a number of variable parameters. The work described in this paper sets out to investigate the adequacy of this model. Firstly, three extensive data sets are used to determine the ranges of building geometry and wind direction for which the model is valid, and to determine the model parameters. It is found that the growth region model is a good descriptor of the pressure field for corners of included angle 60° or more, with wind directions between ±15°, approximately, to the corner bisector. No mature region in the form suggested by Cook was found, although for low height/length ratio buildings a change in flow pattern near the rear of the building was apparent, but not in the form suggested by Cook. The model parameters derived for the growth region were on the whole consistent, and provided useful insights into the mechanics of the vortex system. These parameters were used to predict the measured pressure distributions of a further independent data set and reasonable agreement was found. Future developments and applications of the model are discussed.