An experimental study of the aerodynamic behaviour of high sided lorries in cross winds

Abstract

A recent investigation has shown that in the UK storm of 25/1/90 there were over 400 wind induced accidents of high sided road vehicles that resulted in death or injury, and thus the problems associated with such accidents are becoming of increasing concern. Now over recent years methods have been derived for predicting the wind speeds at which such accidents occur, but these methods depend upon information concerning the aerodynamic forces and moments on such vehicles in cross winds. The experimental work described in this paper set out to obtain a systematic set of such data and to attempt to gain a basic understanding of the flow mechanisms involved. Wind tunnel tests were carried out on a 1 50 th scale articulated lorry model on a bridge deck, in an environmental wind tunnel, with and without a simulation of atmospheric turbulence. Extensive oil flow visualisation tests were carried out and mean and fluctuating values of the aerodynamic force and moment coefficients and surface pressure coefficients were measured. This data enabled spectra, aerodynamic admittances and extreme values of these parameters to be measured. It was shown that the major flow mechanism is a pair of conical vortices over the roof of the trailer similar to those found on the roof of low rise buildings. The nature of these vortices is fairly sensitive to the level of turbulence in the flow, and variations in the surface pressure coefficients and force coefficients with turbulence level are directly related to the changes in these vortices. The unsteady flow measurements indicated that side force oscillations were largely caused by turbulence buffetting, whilst lift force oscillations were dominated by large scale unsteadiness caused by wake vortex shedding.