Free surface flow around a surface-piercing flat plate operating at incidence is a suitable research subject for marine hydrodynamics, because it includes typical flow features found in marine hydrodynamics such as vortex generation, flow separation, and free surface flows. For those reasons, it is selected by the ITTC committee as a benchmarking case for Stereo PIV(SPIV) test. In this paper, flow past a surface-piercing flat plate is studied by computational fluid dynamics (CFD) simulations. The incident angle is 20 degree and the current velocity is 0.4 m/s. Unsteady Reynolds-averaged Navier-Stokes (URANS) simulation is carried out and compared with the existing experimental data. The hydrodynamic forces on the flat plate, velocity profile in the wake regions are presented and analyzed. In addition, the vortical structures are identified and visualized by the Liutex/Rortex method.


Flow around surface-piercing structures involves interactions between current, wave and body and is of importance for ship and ocean engineering. Wave-induced pressure gradient will affect the boundary layer around the submerged body and vice versa, boundary layer will affect the waves of first order forces and moments (Metcalf et al., 2006). On the other hand, the submerged structures are commonly with truncated free end at the bottom and the tip vortices shed from bottom will interact with free surface (Briggs et al., 2019).

Similar physical problems have been extensively studied. Stern et al. (1987) studied the effects of waves on the boundary layer of a surfacepiercing flat plate with an upstream horizontal foil with variable depth of submergence used for generation of Stokes waves in a towing tank for a range of wave steepness and average Re=1.64×106. They observed wedge shaped, broken and turbulent separation region on the free surface.

Metcalf et al. (2006) experimentally investigated the unsteady freesurface wave-induced boundary-layer separation for a surface-piercing NACA 0024 foil in a towing tank at three different Froude numbers, 0.19, 0.37 and 0.55 and three Reynolds numbers, 0.822, 1.52 and 2.26×106. They provided mean and unsteady far-field wave elevations, mean and unsteady foil-surface pressures and analyzed the frequency components of shear layer, Karman shedding, and flapping instabilities, respectively. However, no PIV measurement is conducted in their study.

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