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Twenty-Second Symposium on Naval Hydrodynamics
Marine propellers with various blade geometry such as a highly skewed propeller are often fitted to ships in order to improve the cavitation performance, such as reducing the propeller-induced vibration and noise, or to improve the efficiency of the propeller. In the design of such propellers, the design charts based on methodical series tests are to be supplemented by the theoretical calculations of propeller open-water characteristics. The most familiar propeller design method, for given blade contour configuration and a selected blade section, is the use of lifting-surface theory [1,2]. The radial pitch and camber variations are determined by the lifting surface theory in order to match the given radial loading distribution and chordwise loading shape under the condition of circumferential averaged inflow velocity. In practical propeller design procedure which adopts the commonly used NACA66 thickness form and a=0.8 mean line , pitch and camber variation is determined such that the major loading comes from camber in a circumferential averaged inflow.
Recently, numerous researchers have adopted the Eppler’s theory  to design new blade sections by prescribing pressure distributions over the blade surface in order to improve the cavitation performance. Since Eppler and Shen [5,6,7] introduced Eppler’s design method of a subsonic wing sections into hydrofoil design, Eppler’s method has been widely accepted by the ship researchers and designers as a very good nonlinear and multi-points design method to explore new sections of hydrofoils and marine propellers. It is theoretically and experimentally verified that the cavitation buckets of the new sections are much wider than any other kind of sections such as NACA series.
The application of new blade sections onto propeller blades by Yamaguchi et. al. showed that the cavitation inception was delayed and fluctuating pressure and noise was reduced remarkably. In their first report , a propeller design procedure combining Eppler’s theory and the lifting surface theory were proposed and showed great effect of flat pressure distribution on reducing cavitation volume and fluctuating pressure. In their second report , the influences of designed lift coefficients of new blade sections on the reduction of fluctuating pressure and noise were investigated. The pressure distribution with higher pressure near the leading edge was more effective to increase the open-water efficiency and reduced the noise level. In their third report , the triangular pressure distribution with a negative peak at the leading edge was suggested to stabilize sheet cavitation and to suppress cloud cavity when its generation was possible.
Lee et al.  has suggested a different concept of propeller design procedure by developing a new blade section for a key radius of the propeller and using it onto all radii to avoid the difficulty of a different new section for each radius, and the difficulty of surface fairing and smoothing. Dang et al.  have developed a new and different propeller design procedure using new blade sections, which incorporates Eppler’s design code, the steady and unsteady lifting surface prediction codes and concept of equivalent 2-D sections.
Realization of the three-dimensional pressure distribution, even though it is known, is difficult as a matter of fact, since the Eppler’s theory treats only a two-dimensional foil section. In addition, blade surface fairing is needed after designing every section at each radius to form smooth blade geometry.
This paper shows the design system of marine propellers with new blade sections. The Quasi-Continuous Method (QCM) [2,17], one of the lifting surface theories, is applied to the numerical calculation of the propeller design. The new blade sections with the prescribed three dimensional pressure distributions over blade surface are designed by the numerical optimization technique, i.e. SUMT (Sequential Unconstrained Minimization Technique) method . The new blade section is designed by specifying surface pressure distributions that minimize the cavitation phenomena. For example, surface pressure distributions are prescribed as minimizing the occurrence of local suction peaks at the section leading edge. It is possible to derive the blade sections, which have a superior cavitation performance to those based on the NACA series. Propeller efficiency would be increased by reducing the expanded area ratio while keeping the cavitation performance at the same level as that of the propeller with larger blade area by adapting the propeller with the new blade section which was designed by the present system.
The new propellers for a pure car carrier and a container ship were design by the present system. The model test results of the new propellers, such as open-water characteristics, cavitation patterns and fluctuating pressures induced on the hull, are presented.
2.Design Technique of Marine Propellers with New Blade Sections