Wake modes of rotationally oscillating cylinders at Re=150

The wake structure of a circular cylinder undergoing forced rotary oscillations is studied at Re=150. Cylinder forcing conditions range between 0.17≤θPP≤5.58, where θPP is the peak-to-peak oscillation amplitude in radians and 0.67≤FR≤3.5, where FR is the ratio of forcing frequency to natural shedding frequency. DPIV and spectral analysis are used to obtain quantitative data about the wake structure. Wake modes and their dependence on forcing conditions are identified. These include previously unknown wake modes present at higher frequencies. Wake mode boundaries are identified on the parameter space. These lead to a better understanding of wake formation at low Re.