TURBULENCE STRUCTURE IN INTERMEDIATE WAKE OF A CIRCULAR CYLINDER

Abstract

Turbulence structure in the intermediate wake of a circular cylinder was studied by a conditional-sampling technique. The measurements were made at a section 8 diameters downstream of the centre of the cylinder. Lateral velocity fluctuations at each position of measurement were found to a proper reference signal to make the conditional sampling if they were combined with longitudinal velocity fluctuations along the wake axis. Velocity fluctuations were decomposed into those produced by large-scale coherent structures and those associated with small-scale structures. Maps of streamlines, vorticity, velocity vectors and correlation of velocity fluctuations were presented in the large-scale structures. Intensity, correlation and intermittency of the small-scale fluctuations were also presented and discussed in relation to the flow field in and around the large-scale structures. A mechanism of entrainment by the large-scale structures and diffusion of their vorticity was suggested on the basis of the above results.