Abstract
The present paper focuses on the numerical investigation of the flow around the fully submerged 2D and 3D hydrofoils operating close to a free surface. Iterative boundary element method is implemented to predict the flow field. This study aims to investigate the aspect ratio effect on the free surface interactions and hydrodynamic performance of the hydrofoils under a free surface by using potential flow theory. Three different submergence depths and aspect ratios are studied in the wide range of Froude Numbers. In 3D cases, spanwise width of the numerical wave tank model is selected both equal and wider to the foil span, to observe the sidewall effects. Wave field seems to be two dimensional at low Froude numbers. On the other hand, signs of three dimensionalities are observed on the free surface structure for higher Fn, even the predicted wave elevations are very close to 2D calculations in the midsection. Increment in the Fn give a rise to the amplitude of the generated waves first, however a further increase in Fn has a lowering effect with the beginning of waves spill in the spanwise direction in the form of Kelvin waves. Free surface proximity and resultant wave field are also seeming to be linked with the lift force on the hydrofoil. As aspect ratio of the foil increase, 3D lift values are getting closer to those of 2D calculations. However, it is seen that, 3D BEM predictions of a hydrofoil under free surface effect cannot be considered two-dimensional even the aspect ratio is equal to 8.
Highlights
Using hydrofoils to generate additional lift is a common practice in marine applications
The detailed investigation of the flow field around the 3D NACA 0012 hydrofoil moving beneath the free surface is presented
From the previous analysis, here, free surface width is expanded to 2.0 times of foil span, to observe the wave field created by a finite-span hydrofoil
Summary
Using hydrofoils to generate additional lift is a common practice in marine applications. Wave Field Generated by Finite-Span Hydrofoils Operating Beneath a Free Surface. Shallow submergence alters the flow field around the hydrofoil in term of pressure balance. While the foil approaches through the free surface, it creates a wave field. This wave field is the result of the lower pressure zone at the upper side of the foil: lower pressure between the foil and the surface causes the free surface to deform, reduces the suction and reduces the lift [4]. Generating a wave field unavoidably produces a drag force. Filippas and Belibassakis [5] showed that, free surface proximity acts upon the foil performance alternatively, and in some conditions (operating velocity and submergence ratio) the lift force may increase
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