Kármán street-boundary layer interactions in turbulent flow

The current work investigates how the wake that is shed from a bluff-body obstruction, when immersed within a boundary layer, interacts with the existing turbulent structures. These interactions were studied by placing a circular cylinder normal to a freestream flow within a turbulent boundary layer of Re_τ = O(10³). While previous research has focused on large cylinder diameters (D) in comparison to the boundary layer thickness (δ) (D/δ ~ 6.67 to 1.25), the current work explores smaller D/δ ratios (down to 0.10). Steel cylinders of different diameters were magnetically fixed near the bottom wall of a recirculating water tunnel, and planar PIV was used to measure the velocity fields downstream of the cylinder in its wake region. To explore the impact of the gap size between the cylinder and the channel wall (G) on wake structures, each cylinder was systematically moved away from the channel wall and PIV data were collected. A principal aim of this work is to study the effect of the von Kármán street on the boundary layer characteristics, and vice versa, as captured through instantaneous velocity, instantaneous vorticity, and mean and fluctuating velocity profiles.