Response of a cylinder wake to large-scale coherent structures in a turbulent boundary layer

The wake of a cylinder immersed in a turbulent boundary layer is studied using two-dimensional particle image velocimetry for six wall-normal cylinder positions with the goal of understanding the influence of the large-scale structures in the boundary layer on the evolution of the wake. 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 Reynolds stresses are conditioned on the sign of the local large-scale streamwise velocity field. These results 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 are 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. In this presentation, the results are understood through the large-scale structures' advection and shear influences on the cylinder wake.