Author(s): Riccardo Angelini Rota Roselli; Giuliano Vernengo; Stefano Brizzolara; Roberto Guercio

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Keywords: Smoothed particle hydrodynamics; Free surface flow; Surface-piercing strut; High froude number; Wave breaking

Abstract: We present preliminary results of a study aimed to assess the capabilities of Smoothed Particle Hydrodynamics method in reproducing complicated free surface flow patterns. Specifically, the generation of waves at relatively high Froude numbers (Fn=0.37÷0.55) by streamlined surface piercing bodies with a rounded leading edge. This class of flows presents different interesting fluid phenomena manifesting all at once: forward wave pile-up at stagnation, wave breaking with flow reversal (similar to that observed in “Bidone” type of hydraulic jumps) and flow separation caused by interactions of steep free-surface waves and the turbulent wall boundary layer. Hydrodynamics of surface-piercing bodies is a relevant issue for different engineering fields, coastal and offshore engineering and naval architecture among others. Bridges pylons subject to river stream, the legs of offshore jack-up drilling rigs, submarines sailing at periscope depth, or unconventional surface ships such as Small Waterplane Area Twin Hulls (SWATHs) and hydrofoil crafts are some examples where unsteady free surface flow around slender surface-piercing bodies might strongly affect the performance of the whole craft. The systematic study focuses on the highly unsteady free surface flow pattern observed and measured around a vertical surface-piercing strut advancing at forward constant speed in an initial calm water tank. The strut is a vertical prismatic body obtained extruding a symmetric NACA0024 airfoil section. Detailed experimental characterization of the unsteady flow was obtained towing the strut in calm water at different Froude numbers (based on length), according the apparatus shown in Figure 1. Here we consider the higher speeds, since these cases in particular show a marked flow instability caused by the interaction between turbulent separation and free surface waves. Principal geometrical characteristics of the towed body and the tank are given in Table 1. This case has been used to validate unsteady RANSE solvers with free surface capturing algorithms and turbulence methods.

DOI: https://doi.org/10.3850/978-981-11-2731-1_364-cd

Year: 2018