On circular cylinders undergoing two-degree-of-freedom forced motions

Cylinders undergoing one- and two-degree-of-freedom (DoF) motions were stud ied. Since the forces on the cylinder fluctuate in both the streamwise and transverse direction, it is believed that such motions are more natural tha n transverse-only vibrations. A set of experiments was conducted in a water tunnel using both digital particle image velocimetry (DPIV) and force meas urements. Several qualitative differences were noted, including a dramatic increase in phase coherence and the disappearance of the "2P" mode. It appe ars that the transverse motion sets the frequency of shedding, and the stre amwise motion the relative phase therein. (C) 2001 Academic Press.