Wind-tunnel modelling of the Silsoe Cube

Abstract

1:40 scale wind-tunnel modelling of the Silsoe 6 m Cube at the University of Auckland is reported. In such situations, it is very difficult to model the full turbulence spectra, and so only the high-frequency end of each spectrum was matched. It is this small-scale turbulence that can directly interact with the local flow field and modify flow behaviour. This is illustrated by studying data from tests conducted in a range of European wind tunnels. It is recommended that spectral comparisons should be carried out by using turbulence-independent normalising parameter, such as plotting fS( f)/ U 2 against reduced frequency f= nz/ U. Using parameters such as the variance and integral length scale can easily mask major differences. It is noted that it is the size of the tunnel that limits the low-frequency end of the spectra, and so the longitudinal and transverse turbulence intensities were lower than in full scale. In spite of this similar pressure distributions are obtained. Some differences are observed and these are partially attributed to the reduced standard deviation of wind directions, which affects both the observed mean and peak pressures by reducing the band of wind directions occurring during a run centred on a particular mean direction. The reduced turbulence intensities also affect the peak-to-mean dynamic pressure ratio. However, since the missing turbulence is at low frequencies, the peak pressures appear to reduce in proportion. By expressing the peak pressure coefficient as the ratio of the extreme surface pressures to the peak dynamic pressure observed during the run, reasonable agreement is obtained. It is argued that this peak–peak ratio is also less sensitive to measurement system characteristics or analysis method, provided the measurement and analysis of the reference dynamic pressure is comparable with that used for the surface pressures.