Free surface effects on a rotating cylinder

Flow around a circular cylinder is a canonical bluff body flow which has widespread fundamental importance in fluid mechanics. Many studies have focused on the vortex shedding from static or rotating cylinders subjected to a uniform free stream and usually neglect end effects. Studies considering end effects have primarily focused on the bottom wall whereas much less attention has been paid to cylinder-free surface interactions characterised by a run-up and a depression of the free surface. We present new results which investigate the free surface effects on a flow around a static and rotating cylinder with 900<Re<5000, mounted vertically in an open water channel. At each ????, we vary the rotational frequency of the cylinder using a stepper motor. Particle image velocimetry measurements are conducted over the midplane downstream of the cylinder in the streamwise-wall-normal direction to capture the flow field from the free surface (y/d = 0) to the free stream region (y/d = -12.5). Additional measurements are also performed over the cross-sectional planes near the free surface and in the free stream region. Over the range of rotation rates investigated, we observe different shedding mechanisms in the free stream and free surface regions which will be presented in the meeting.