Experimental study of oscillatory flow interaction with a wall-mounted horizontal circular cylinder

Flow behaviour and hydrodynamic forces have been measured for sinusoidal oscillatory flows interacting with a wall-mounted horizontal circular cylinder. The experiments cover 4 ≤ KC ≤ 165 and 1.3×103 ≤ Rec ≤ 5×104. Measurements were made with the cylinder placed on a smooth wall and on an engineered rough wall to determine the effect of wall roughness on the flow and force dynamics. The roughness of the rough wall and the properties of the oscillatory boundary layers over the two walls are established from velocity profiles measured without the cylinder present. The dynamics of the vortex produced in the lee of the cylinder in each flow half-cycle are measured using particle image velocimetry, and in-line and lift forces are measured using two 6-axis load cells built into the test cylinder. Results are presented for the KC-dependent and roughness-dependent vortex dynamics, near-cylinder velocities, and intra-period force behaviour. At low KC, the lee vortex tracks close to the cylinder as it accelerates up and over the cylinder soon after free-stream flow reversal, resulting in high vortex-induced near-cylinder velocities and forces. As KC increases, the vortex tracks further from the cylinder and its influence on the near-cylinder velocities and forces diminishes. For KC ⪆ 50 rough-wall forces are lower than smooth-wall forces because of more-distant vortex tracks and lower wall boundary layer velocities. Force coefficients show similar dependence on KC as seen in previous studies.