Secondary currents and heat transfer in flow around a cylinder mounted in a narrow channel: LES and PIV

We report on Large-Eddy Simulations (LES) and Particle Image Velocimetry (PIV) of flow around a short cylinder mounted in a narrow infinite plane channel at a Reynolds number of 3750 based on the bulk flow velocity and cylinder diameter. While the front of the cylinder is featured by a set of typical horseshoe vortices, in the near wake we discover quasi-periodic low-frequency secondary motion in the form of a pair of counter-rotating vortices. The Karman vortex street remains the dominant pattern, but further downstream from the cylinder the prevailing motion that transports smaller-scale structure and associated momentum and heat across the narrow channel in the verical direction are the secondary streamwise vortices, as also previously observed in slot jets. We focus on the impact of secondary flows on heat transfer in front of the cylinder intensified by the horseshoe vortices as well as in the near and far wake further downstream in the form of streamwise vortices.