Response of Cylinder Wake to Large-Scale Turbulent Boundary-Layer Structures

The wake of a cylinder immersed in a turbulent boundary layer is studied using two-dimensional particle image velocimetry for six cylinder positions. The axis of the cylinder is positioned in the spanwise direction, and particle image velocimetry is performed in the streamwise–wall-normal plane from just downstream to three boundary-layer thicknesses downstream of the cylinder. Time-averaged and conditional statistics of the Reynolds stresses are analyzed and compared with statistics of the unperturbed turbulent boundary layer. The conditional analysis is used to understand the influence of large-scale turbulent structures on the evolution of the cylinder wake. The Reynolds stresses are conditioned on the sign of the local large-scale streamwise velocity field. The conditioned Reynolds stresses show that the large-scale turbulent structures affect the wake fluctuation amplitude, symmetry, and position as the wake evolves downstream. Depending on the sign of local large-scale turbulent structures, the amplitude of cylinder wake Reynolds stresses is observed to change by as much as 15%, while the position of the wake varies by as much as 10% of the boundary-layer thickness. The results are understood through the large-scale structures’ advection and shear influences on the cylinder wake.