• Document: Optimization of the Propeller with ECO-Cap by CFD
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Fourth International Symposium on Marine Propulsors smp’15, Austin, Texas, USA, June 2015 Optimization of the Propeller with ECO-Cap by CFD Kenta Katayama, Yoshihisa Okada, Akinori Okazaki Propeller Design department, Nakashima Propeller Co.,Ltd. 688-1, Joto-Kitagata, Higashi-ku, Okayama 709-0625, Japan E-mail: ken-katayama@nakashima.co.jp – Web page: http://www.nakashima.co.jp ABSTRACT The authors developed a new special cap which was named It is considered that the propeller efficiency is improved by ECO-Cap in order to increase efficiency and to avoid rudder weakening propeller hub vortex. On that account, the erosion by reducing hub vortex. The purpose of this paper is behavior of the hub vortex which was generated behind to predict ECO-Cap performance by CFD and to verify the general propeller caps was investigated by computational prediction by model test and monitoring FOC (fuel oil fluid dynamics analysis and a special cap, named ECO-Cap, consumption) at a vessel in service. was developed and optimized which has small 7 fins to prevent the hub vortex generation. Furthermore, the effect of ECO-Cap was verified by model test and by monitoring 2 ANALYSIS BY CFD the fuel oil consumption at a vessel in service. 2.1 Propeller particulars and analysis model CFD analyses of two propellers were carried out. Propeller- Keywords A was 6 bladed highly skewed with large blade area CFD, Propeller, Hub vortex, Energy saving device, ECO- propeller for large container vessel and Propeller-B was 5 Cap, Rudder erosion. bladed semi skewed with small blade area propeller for bulk carrier. 1 INTRODUCTION Table 1 and Figure 1 show the propeller particulars and In recent years, the ship speed and propeller loading profiles. These propellers were designed to confirm the increase more and more. Especially, the tendency is performance of the propeller with cap. remarkable in container ship. When the horsepower per unit Table 1: Propeller particulars area is 700-800 kW/m2 or more and the ship speed is 22-23 knots or more, Mikael Grekula et al.1) pointed out the Propeller A Propeller B problem of rudder erosion. Juergen Friesch2) described the Number of blades - 6 5 causes of rudder erosion were propeller tip-vortex cavitation and propeller hub-vortex cavitation and he introduced new Dia. (Model/Actual) mm 240 / 9500 265 / 6700 twisted rudder TW05 to reduce the risk of cavitation erosion Pitch ratio at 0.7R - 1.043 0.833 in his paper. Exp. area ratio - 0.81 0.44 Yamasaki et al.3) developed Non-Hub Vortex (NHV) propeller, features of this NHV propeller has confirmed an increase in efficiency by reducing the hub vortex. It is known that PBCF (Propeller Boss Cap Fins) which was developed by Ouchi et al.4) has similar effect. Kawamura et al.5) investigated the characteristics of PBCF at the model and full scale Reynolds number by CFD (Computational Fluid Dynamics) analysis. Recently, several special caps in order to increase the propeller efficiency have been developed by some manufacturers or shipyards. Those special caps were expected to avoid rudder erosion as well as improve propeller efficiency. (a) Propeller-A (b) Propeller-B 22nd ITTC (The International Towing Tank Conference) appointed the Specialist Committee on Unconventional Propulsors6) described that the power saving or efficiency Figure 1: Profile of Propellers gain of PBCF expected at the full scale will be 2 to 3 times greater than the model scale predictions in their final report. RANS calculations were performed by SOFTWARE Figure 4 shows the pressure distribution behind the CRADLE SCRYU/Tetra Ver.10 which is a commercial propeller caps in the result of CFD analyses. Reynolds CFD code and is based on a finite volume method with an number was abt.2 x106 in this analyses. Blue part indicates unstructured grid. The Shear Stress Transport k-ω model negative pressure by hub vortex. was applied to the turbulence model. The authors s

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