The vortex-induced vibration of an elliptic cylinder with different aspect ratios

This study investigates the hydrodynamic characteristics of an elastically-mounted elliptic cylinder at low mass ratio m*=2 and low damping ratio ζ=0.007. The aspect ratio (AR) defined by the characteristic length in the streamwise and transverse direction varies in the range 0.5≤AR≤2.0. The dynamic response is characterized as a function of reduced velocity. The streamlined profile of the elliptic cylinder results in a delay of the vortex shedding and a diminished strength of the averaged vorticity. However, the hydrodynamic characteristics become more complicated for large ARs. Both the response amplitude and the hydrodynamic forces acting on the cylinder are enhanced as the afterbody is reduced. The PSD behaviors show the existence of four different flow regimes. Several new pertinent modes, such as 2 Po*, 2T*, etc., are captured through flow visualizations. A comprehensive analysis of the vortex shedding indicates the sub-vortices generated at the rear of the cylinder plays a key role in the formation and evolution wake modes. Besides, the time-averaged vorticity magnitude at the vortex core elucidate that despite secondary vortices account for a large proportion of the primary vortices, they only make a small contribution to the suppression of the vibration amplitude.