Flow Interactions Between Streamwise-Aligned Tandem Cylinders in Turbulent Channel Flow

The flow interactions between streamwise-aligned wall-mounted circular cylinders is studied experimentally to explore shear-layer interactions that lead to modifications of the flow around the downstream-most cylinder. Two identical finite-length cylinders are arranged in tandem and fully submerged in the log layer of turbulent channel flow, and particle image velocimetry measurements are conducted to document the flow behavior at various streamwise spacings. Comparisons are made to flow around an isolated cylinder as well as the baseline case of smooth-wall turbulent channel flow with no cylinders present. Strong interactions between the shear layers shed by each individual cylinder are noted, whereby the downstream-most wake exhibits a weaker, more spatially compact recirculation region and significantly reduced reattachment length as compared to flow around an isolated cylinder. First- and second-order turbulence statistics show similar wake modifications, particularly for small cylinder spacings where the shear layer shed from the top of the upstream cylinder directly impinges on the downstream-most cylinder and significantly reduces the turbulence levels in the downstream shear layer. Increasing the spacing of the cylinders relaxes the turbulence statistics in the shear layer of the downstream-most cylinder back toward those of an isolated cylinder, although even a spacing of eight cylinder diameters is not sufficient to fully recover isolated cylinder behavior. Finally, the impact of the cylinder aspect ratio is considered is found to have only a modest impact on the observed trends in reattachment and shear-layer interactions between the cylinders.