Assessment of vortex lock-in for circular cylinders in an in-line tandem configuration

Understanding the characteristics of structures arising from vortex shedding in a tandem cylinder configuration is important in the design of wind turbine farms, bridges or offshore platforms. An experimental study is conducted on the interaction of the flow behind two circular cylinders in an in-line tandem configuration with an acoustically driven oscillating pipe flow. Three cylinder diameters, d_c, are studied over a Reynolds number range of 900-9500. The flow has a non-zero mean velocity, ū, with forcing frequency of 760Hz while the forcing amplitude is varied between 0-30\% of ū. The downstream cylinder location is fixed at a velocity node of the acoustic mode while the upstream cylinder is positioned at distances of 1.5d_c, 3d_c and 6d_c corresponding to the extended body, the reattachment and the co-shedding regimes respectively. Measurements of the flow was carried out through hot-wire anemometry and high speed planar PIV. Initial results show that cylinders in the extended body regime and a single cylinder at a velocity node share similar vortex lock-in behaviour. Further, in the co-shedding regime it is possible to induce vortex lock-in on a cylinder at the velocity node by having a second cylinder sufficiently far upstream. It is hypothesized that vortex shedding from the upstream cylinder is responsible for such a trend. PIV velocity fields will be analysed in order to better understand this behaviour.