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Abstract

Wind tunnel tests were conducted in a simulated atmospheric boundary layer on a model of a circular, single-cell building possessing a dominant circular wall opening. The roof of the model was either rigid or made from a flexible membrane material with a variable tension and the internal volume of the model was also adjustable in discrete increments. A total of one hundred and fifty model configurations were investigated; five different roof tensions, three cavity volumes, two windspeeds and five opening azimuth angles.

The local mean external pressure distribution around the model was insensitive to changes in Reynolds number over the range 1,4xl05 < Re < 2.5xl05, whereas, the mean internal pressure distributions were self-similar for Reynolds numbers above 1.8xl05. Reynolds numbers were based upon the diameter of the model and the mean windspeed at roof height and for Reynolds numbers above 1.8xl05 the mean internal pressures were equal to those measured on the external walls.

Attention was focussed on the steady-state dynamic response of the cavity pressure within the model and its sensitivity to changes in the flexibility of the roof. It was shown that turbulent buffetting present on the external wall pressure spectra was transmitted to the internal pressure fluctuations and that the phenomenon of Helmholtz oscillation, due to resonance of the air contained within the dominant opening, occurred for all the configurations tested.

Increased damping of the Helmholtz mode was effected by increasing the flexibility of the roof, increasing the mean windspeed, increasing the cavity volume and rotating the opening away from the line of the approach flow. Indeed, differences in the magnitudes of the internal and external root-mean-square pressures were attributed to changes in the magnitude of the resonant peak due to Helmholtz oscillation. An apparently universal relationship between the magnitude of the measured spectral response at the Helmholtz frequency and cavity volume scaling was determined.

Comparisons between the measured and predicted magnitudes of the ratio of internal to external pressure fluctuations, using the theoretical approach of Vickery & Bloxham (1992), were satisfactory when the opening was oriented to windward whilst at other azimuth angles the theory overestimated the root-mean-square cavity pressure. However, it was concluded that accurate determination of the empirical loss and inertia coefficients may improve these comparisons.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology > TA Engineering (General). Civil engineering (General)
Departments:	School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses School of Science & Technology > Engineering

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