Printed in Great Britain 269 The distortion of turbulence by a circular cylinder

The flow of grid-generated turbulence past a circular cylinder is investigated using hot-wire anemometry over a Reynolds number range from 4.25 x lo3 to 2.74 x lo4 and a range of intensities from 0.025 to 0.062. Measurements of the mean velocity distribution, and r.m.s. intensities and spectral energy densities of the turbulent velocity fluctuations are presented for various radial and circumferential positions relative t o the cylinder, and for ratios of the cylinder radius a to the scale of the incident turbulence L, ranging from 0.05 to 1-42. The influence of upstream conditions on the flow in the cylinder wake and its associated induced velocity fluctuations is discussed. For all measurements, detailed comparison is ma,de with the theoretical predictions of Hunt (1973). We conclude the following. (i) The amplification and reduction of the three components of turbulence (which occur in different senses for the different components) can be explained qualitatively in terms of the distortion by the mean flow of the turbulent vorticity and the ‘blocking’ or ‘ source ’ effect caused by turbulence impinging on the cylinder surface. The relative importance of the first effect over the second increases as alLz increases or the distance from the cylinder surface increases. (ii) Over certain ranges of the variables involved, the measurements are in quanti-tative agreement with the predictions of the asymptotic theory when alL, 4 1, a /Lz 9 1 or lkla (iii) The incident turbulence affects the gross properties of the flow in the cylinder wake, but the associated velocity fluctuations are probably statistically independent of those in the incident flow. (iv) The dissipation of turbulent energy is greater in the straining flow near the cylinder than in the approach flow. Some estimates for this effect are proposed. 1