Vortex-induced Vibrations under Periodically Oscillating Flow

Laboratory experiments were conducted to investigate the vortex-induced vibrations (VIVs) of a one-degree-of-freedom elastically mounted cylinder in a periodically fluctuating stream within a water channel. The study examined cylinder vibration patterns, hydrodynamic loads, and wake flow dynamics across a wide range of reduced velocities, incoming flow fluctuation frequencies, and flow fluctuation amplitudes using time-resolved particle image velocimetry and a high-resolution load cell. The findings indicated that fluctuating incoming flow reduces cylinder vibration amplitudes, with vortex hydrodynamic loads exhibiting an 'out-of-phase' pattern with cylinder dynamics at lower reduced velocities. Analysis of wake flow dynamics revealed a continuous shift between '2S' and '2P' vortex shedding modes, showing a distinctive hysteresis effect in relation to instantaneous incoming water flow speeds. Furthermore, phase-averaged hydrodynamic load analysis showed that increased incoming flow fluctuation intensities can result in stronger 'out-of-phase' hydrodynamic loads during periods of decreasing incoming flow speeds.