NUMERICAL MODELING OF HEAVY PLANING HULLS AND HIGH LIFT HYDROFOILS AT MODERATE FROUDE NUMBERS

Miles Wheeler

This dissertation is focused on heavily loaded planing hulls and high-lift hydrofoils operating in moderate Froude-number regimes, which are important for a variety of military and civil marine applications. The research described here entails high-fidelity computational fluid dynamics simulations of flows around prismatic planing hulls and surface-piercing hydrofoils. The physical models involved in numerical simulations include viscous, multi-phase, turbulent, and unsteady phenomena. Verification and validation studies for all considered problems have been conducted, followed by parametric studies of selected hull and hydrofoil configurations. The planing-hull investigation analyzed constant-deadrise hulls with various bow shapes. Both normal and heavily loaded conditions were considered in broad speed regimes from the displacement to planing mode and two characteristic locations of the center of gravity. The hull with a concave bow was found to perform best, as it had lower drag at transitional speeds in the overloaded state and lower drag at fastest speeds at normal loading.\nThe high-lift flexible hydrofoils having isotropic and orthotropic material properties, which imitate composite structures, were numerically modeled in calm water and in head waves. To investigate fluid-structure interactions associated with flexible hydrofoils, numerical solutions were obtained using coupled fluid and solid solvers, as well as morphing and overset meshing methodology. Effects of materials properties on hydrodynamic characteristics and structural deformations of hydrofoils were determined. Specifically, orthotropic hydrofoils with fibers directed from the fixed root to the leading edge exhibited negative twist, lower lift coefficients in calm water and lower lift oscillations in waves. Hydrofoils with fibers oriented towards the railing edge manifested higher twist and lift forces in calm water, and larger oscillations in wave conditions. \nAdditional studies of high-lift surface-piercing hydrofoils subjected to ventilation by atmospheric air were conducted. The air ventilation usually results in substantial decrease of the lift force. To counteract this process, an application of small fences on the foil surface was numerically investigated. It was found that these elements can suppress air ventilation, thus increasing lifting capabilities and improving lift-drag ratio of hydrofoils at moderate Froude numbers.

NUMERICAL MODELING OF HEAVY PLANING HULLS AND HIGH LIFT HYDROFOILS AT MODERATE FROUDE NUMBERS

Files and links (1)

Abstract

Metrics

Details