Abstract
Abstract. Surface-piercing propellers have been widely used in light and high-speed vessels because of their superior performance. Experimental study of these propellers is one of the most reliable and accurate ways which can provide details about the performance and effect of different design parameters on the performance of the surface-piercing propellers. In this research, a five-blade surface-piercing propeller was tested in the free surface water tunnel of Babol Noshirvani University of Technology in order to expand the available experimental data and database for future engineering designs. The effects of immersion ratio and shaft inclination angle on the propeller's efficiency and hydrodynamic coefficients were examined. A free surface water tunnel and a calibrated dynamometer with the measurability of the thrust forces and the torque of a propeller were used for this purpose. Comparing the obtained results with the existing semi-experimental equations shows that the equations presented in various geometric conditions are not accurate enough, and developing the existing database is necessary. The details of the obtained results showed that the hydrodynamic coefficients of the thrust and torque increased by increasing the immersion ratio, but the coefficient of hydrodynamic thrust and efficiency reduced. The results also indicated that the coefficient of torque increased by increasing the shaft inclination angle. The highest efficiency of the propeller was achieved in the range of 40 %–50 % immersion ratios at all angles of shaft inclination. For all immersion ratios, the maximum and minimum efficiencies were obtained at 0 and 15 shaft inclination angles, respectively. The best efficiency of the propeller was at 50 % immersion ratio and zero shaft inclination angle.
Highlights
Today, more than 90 % of world trade belongs to marine transportation because of the low cost of transferring passengers, goods, and raw materials (IMO, 2012)
First, the results of a surface-piercing propeller test in different test conditions were compared to the hydrodynamic coefficients predicted by semi-experimental equations of Ferrando et al (2007) and Montazeri and Ghassemi (2009)
Both semi-experimental equations can correctly predict the increase in hydrodynamic coefficients by an increasing immersion ratio, the difference between the values predicted by these equations with the experimental tests, especially for the thrust, shows that these equations are not accurate enough
Summary
More than 90 % of world trade belongs to marine transportation because of the low cost of transferring passengers, goods, and raw materials (IMO, 2012). Surface-piercing propellers are a special kind of super-cavitating propeller which act in semisubmerged conditions and on free surfaces They are known as one of the suitable propulsion systems for increasing speed and are able to create thrust in different conditions. Based on the current design process for the selection of propellers, the most important step is determining the minimum thrust and maximum torque of the propeller. These values can be obtained from the hydrodynamic coefficients that are determined by experimental, theoretical, and semiexperimental methods. Despite developing theoretical methods, using physical modeling and experiments is still the most reliable method for designing the surface-piercing propellers
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