Numerical study of the effect of submergence depth on hydrokinetic energy conversion of an elastically mounted square cylinder in FIV

The FIV (Flow-Induced Vibration) responses of an elastically mounted square cylinder near a free surface are numerically investigated using 2-dimensional RANS equations in conjunction with SST k-ω turbulence model. In this work, the effect of submergence depth on the FIV response and energy conversion is studied. The flow field behavior for flow velocities between 0.2 m/s and 2.5 m/s (1.61 × 10⁴<Reynolds number<2.02 × 10⁵) is examined. By comparing with experimental data, the numerical model is verified. FIV consists of VIV (Vortex-Induced Vibration) at low flow velocities and galloping at high flow velocities. The FIV responses, wave profile, and energy conversion performance are discussed in detail. The main conclusions are: (1) Decreasing the submergence depth ratio suppresses the FIV amplitude, resulting in an obvious decrease in energy conversion. (2) At very low submergence depth ratios, the wave and breaking wave phenomenon are significant. Meanwhile, the vibration is unstable when the square cylinder is closely approaching the deformed free surface. (3) Decreasing the submergence depth ratio also delays the onset of galloping. (4) The maximum amplitude and power appear at the end of the galloping region. (5) The maximum FIV energy conversion efficiency is obtained in the VIV region.