Performance prediction of a hydrofoil near the free surface using low (BEM) and high (RANS) fidelity methods

Abstract

As a first step toward a multi-fidelity optimization tool for hydrofoils, the present work assesses the ability of the in-house code PUFFIn to be used as a “low-fidelity” solver within the multi-fidelity framework. The code, based on the Boundary Element Method (BEM) and the potential flow theory, is used to study the performance of a typical windsurf hydrofoil operating near the free surface. The hydrofoil is composed of a front wing and a rear stabilizer in a plane-like configuration. Computations are performed for single body configurations (only one wing) and two-body configurations (front wing and stabilizer). First, three linearized models of the free surface are compared for the single front wing configuration with several values of the Froude number: the symmetry, anti-symmetry and Neumann-Kelvin conditions. The results show that for relatively high Froude number, the anti-symmetry and the Neumann-Kelvin conditions provide very similar forces. Then, the predictions of the BEM solver are compared with “high-fidelity” RANS computations, in terms of pressure drag and lift, pressure distribution on the hydrofoil and free surface elevation. Several Froude numbers and submergence depths are studied. The global lift and drag variations predicted by the BEM with the anti-symmetry and Neumann-Kelvin conditions on the single-body configurations are similar to the RANS predictions. For the two-body configurations, the Neumann-Kelvin condition outperforms the anti-symmetry condition. Based on the BEM/RANS comparison, the potential flow solver reveals to be a relevant tool for multi-fidelity optimization.