Vortex shedding from a yaw-oscillating circular cylinder in subcritical flow

This study investigates vortex shedding characteristics from a circular cylinder subjected to yaw oscillations. The study considers two length-to-diameter ratios (13 and 20) and two Reynolds numbers ( 5x10(3) and 1.5x10(4)). Yaw oscillations ranging from theta=0 degrees to 30 degrees are considered at various reduced frequencies from 0.25 to 4. Vortex shedding behavior at the mid-span of the cylinder is measured using hot-wire anemometry. Planar particle image velocimetry (PIV) measurements at the mid-span are used to visualize the near wake. It is shown that an increase in the reduced frequency leads to a shift in the frequency range of vortex shedding toward lower values. Vortices are shed nearer to the base of the cylinder, and vortex shedding becomes more disorganized with increasing reduced frequency. Based on phase-averaged analysis of vortex shedding, the validity of the independence principle (IP) diminishes during the first half cycle beyond theta=15 degrees at low reduced frequencies and beyond theta=20 degrees at moderate reduced frequencies. In the return cycle, the deviation from the IP increases with increasing reduced frequency. The IP prediction is re-established at low yaw angles during the return cycle and for low reduced frequencies. Increasing the length-to-diameter ratio enhanced the organized vortex shedding and elevated the shedding frequency for both static and yaw-oscillating cylinders.