Wind loadings on the television tower, Hamburg, Germany

To find more detailed information about the flow around circular cylindrical structures at very high Reynolds number (up to 1.8 × 107) wind-pressure measurements were carried out on the tapered reinforced-concrete television tower in Hamburg, West Germany. The tower is situated in the centre of the city, but the surrounding buildings are relatively low (mean height ∼ 20 m). The prevailing wind direction is from the near-by sea (northwest); the country is flat. The static reference pressure was found by using the pressure distribution around the cylindrical tower shaft, with the assumption that the zero angle of the pressure distribution is at φ0 = 34° (depending on Reynolds number). Given the position of the stagnation point and the pressure at this point, it was possible to calculate the instantaneous wind speed and direction. For two years, various records of 20 minutes' duration, at Reynolds numbers between 6 × 106 and 1.8 × 107, were obtained. The pressure distribution was found to have markedly non-stationary behaviour, which leads to very high peaks in the drag and lift coefficients. The power spectra of the instantaneous lift coefficient show a distinct peak at the Strouhal number of S = 0.23, which indicates a regular vortex separation. The relation between gust duration and the time taken for the full drag due to a given gust to develop was deduced. An important effect is caused by the fluctuating wind direction. Because of the inertia of the air stream, the pressure distribution becomes asymmetrical, giving rise to a high lift force and an increase in the drag. For practical use, the dependence of the aerodynamic coefficients on the mean wind velocities is analysed.