Organization in a turbulent near-wake

Abstract

The streamwise evolution of the turbulence structure in the near-wake of a cylinder has been quantified using data from an array of eight X-probes in the plane of mean shear. The relative probability of detections of large scale vortical structures on opposite sides of the centreline indicates that the spatial arrangement of these structures can vary in a continuous manner between a dominant alternating (antisymmetric) mode and an opposing (symmetric) code. At a distance of ten diameters from the cylinder, the contributions from the alternating mode to the lateral turbulence intensity v2 and Reynolds shear stress ū are appreciable. These contributions are discussed in the context of the main topological features of this mode. Contributions to 2 and ū from the opposing mode increase with distance from the cylinder. The opposing mode makes a significant contribution to the longitudinal turbulence intensity, especially near the centreline.