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The tip leakage vortex (TLV) cavitation is investigated by a commercial Reynolds averaged Navier-Stokes (RANS) solver. A referenced test on a NACA0009 hydrofoil is used to validate the numerical simulation. Considering the local rotation characteristics of the vortical flow, a rotation-curvature corrected Shear-Stress-Transport model (SST-CC model) is applied to simulate the time-averaged turbulent flow. Compared to the original SST model, the SST-CC model improves the prediction of the velocity in TLV on the measured sections in downstream, and the vorticity and pressure features along the TLV trajectory are analysed numerically. In order to increase the prediction accuracy for the TLV cavitation, the empirical condensation coefficient (Fc) in Zwart's cavitation model is calibrated based on the referenced experiment. By introducing a vortex identification parameter (f∗) related to the strain rate tensor and the vorticity tensor, a relationship between the Fc and f∗ is built, and the effects of the rotational motion of the vortex on the cavity are embodied in a modified Zwart's cavitation model. Compared to the conventional Zwart's cavitation model, the modified cavitation model significantly improves the prediction of the TLV cavitation and gets a better agreement with the referenced test on different conditions with various gap widths.

Fairing is one of the most effective devices to suppress vortex-induced vibration (VIV) of marine risers. However, when the rotational friction coefficient of the fairing device is too high to rotate, severe galloping oscillations occurs. In this paper, a two-dimensional mass-spring-damping system was constructed based on the commercial software ANSYS. The galloping mechanism and the two degree-of-freedom (DOF) galloping characteristics of the fairing were studied by numerical methods. In particular, the influence of the natural frequency ratio of the in-line (IL) direction and the cross-flow (CF) direction on the galloping oscillation was discussed. The mass ratio of the riser-fairing system for which the simulations were performed was 1.7, and the damping ratio was 0.003. The Reynolds number based on the cylinder diameter and the inflow velocity was 1000. The range of reduced velocities based on the natural frequency in the CF direction was 1.76–18.52. The results showed that the activation of the inherent modes of the structure and the reattachment of the shear layer in the wake had an important contribution to the generation of the galloping. The movement in the IL direction could promote the reattachment of the shear layer to a certain extent, thereby expanding the scope of the galloping conditions. When the natural frequency ratio was equal to 1 or 2, a “double peak” phenomenon was found in the vibration amplitude curve in the CF direction. In the 2-DOF vibration, the fairing moved in the shape of an “8″ or a drop-shaped trajectory in most cases. On the whole, the interaction between the movement of the fairing in the IL direction and the movement in the CF direction could not be neglected, and the natural frequency ratio also significantly affected the vibration characteristics.