Unsteady wind loading on a wall

This paper presents an extensive analysis of unsteady wind loading data on a 18 m long and 2 m high wall in a rural environment, with the wind at a range of angles to the wall nor mal. The data is firstly analyzed using standard statistical techniques (moments of probability distributions, auto- and crosscorrelations, auto- and cross-spectra etc.). The analysis is taken further using a variety of less conventional methods - conditional. sampling, proper orthogonal decomposition and wavelet analysis. It is shown that, even though the geometry is simple, the nature of the unsteady flow is surprisingly complex. The fluctuating pressures on the front face of the wall are to a great extent caused by the turbulent fluctuations in the upstream flow, and reflect the oncoming flow structures. The results further suggest that there are distinct structures in the oncoming flow with a variety of scales, and that the second order quasi-steady approach can predict the pressure fluctuations quite well. The fluctuating pressures on the rear face are also influenced by the fluctuations in the oncoming turbulence, but also by unsteady fluctuations due to wake unsteadiness. These fluctuations have a greater temporal and spatial coherence than on the front face and the quasi-steady method over-predicts the extent of these fluctuations. Finally the results are used to check some assumptions made in the current UK wind loading code of practice.