Relationship between resistance and air cavity on the bottom surface of V- and W-shaped stepped planing hulls

Abstract

ABSTRACT The formation of air cavities can reduce hydrodynamic resistance, particularly when facilitated by stepped components on the bottom surface of a planing hull. This study aims to investigate the influence of air cavities on the hydrodynamic performance of planing hulls with V- and W-shaped steps using a numerical approach. The Reynolds-averaged Navier-Stokes equations, coupled with the Volume of Fluid method, are employed to capture the air-water interaction in free-surface flow around these hull geometries. A numerical benchmark study, based on Taunton's experimental data, is conducted for validation. The results indicate that the volumetric Froude number and the formation and distribution of air cavities significantly influence the wetted bottom surface area of the planing hull and, consequently, the resistance characteristics. The W-shaped step demonstrates better control over air cavity formation compared to the conventional V-shaped step. The effects of the first, second, and third steps in both configurations are analyzed, along with a quantitative assessment of the pressure distribution induced by air cavities. At volumetric Froude numbers Fr ∇ = 1.109 ± 0.8% and 4.087 ± 0.4%, the step geometry is shown to affect flow behavior and optimize air cavity formation. The increased number of triangular edges in the W-shaped step effectively reduces frictional resistance, enhancing hydrodynamic performance for future hull designs.

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