Abstract
This paper focuses on the ducted propulsion with the accelerating nozzle, and discusses the influence of its fluid acceleration quality on its propulsive performances, including the hull efficiency, the relative rotative efficiency, the effective wake, and the thrust deduction factor. An actual ducted propulsion system is used as an example for computational analysis. The computational conditions are divided into four combinations, which are provided with different propeller pitches, cambers, and duct lengths. The method applied in this study is the Computational Fluid Dynamics (CFD) technology, and the contents of the calculation include the hull's viscous resistance, the wave-making resistance, the propeller performance curve, and the self-propulsion simulation in order to obtain the ship's effective wake, thrust deduction factor, hull efficiency, and relative rotative efficiency. The performance curve of the propeller and resistance estimation results are compared with the experimental values for determining the correctness of the self-propulsion simulation. According to the computational analysis, it is known that increasing the propeller pitch cannot effectively increase the hull efficiency. The duct acceleration quality can be reduced by shortening the duct length; hence, when the effective wake fraction and thrust deduction factor decrease, the hull efficiency is increased. In addition, the pressure inside the duct is relatively low if the acceleration quality of the duct is too high, which is unfavorable for controlling the propeller cavitation. Moreover, if the hull bottom in front of the propeller is tapered up from the front to the back at an overly steep angle, the thrust deduction factor will be too large and lead to a relatively low hull efficiency.
Highlights
The ducted propeller, given its multiple excellent characteristics, has been used increasingly on a variety of vessels in recent years
Huuva [3] discussed the two-phase flow problem that resulted from the Reynolds-averaged-Navier-Stokes (RANS), Detached-Eddy Simulation (DES), and Large-Eddy simulations (LES) equations
This study refers to the calculation settings and methods mentioned by Kao et al [10], and compares the calculation results on the propeller performance and resistance estimation with the experimental values to determine the correctness of the self-propulsion simulation
Summary
The ducted propeller, given its multiple excellent characteristics, has been used increasingly on a variety of vessels in recent years. Yang et al [4] employed the commercial software Fluent with the k-ω turbulent model to conduct the self-propulsion simulation of large oil tankers They found that the axial wakes calculated at the circumferential positions, except for the 180◦ position (six o’clock position), are close to the measured values. Vaz et al [6] applied the MARIN ReFRESCO program proposed in Vaz et al [7] and AcuSolve to predict the flow field of the DARPA SUBOFF submarine They analyzed the maneuvering quality, and found that the difference between the numerical simulations and the measured values was within the acceptable range. Kao et al [10] used the CFD for the self-propulsion simulation of the DARPA SUBOFF submarine They compared the simulation results with the measured values of Vaz et al [6], and found that the maximum error was only 3.5%. This study refers to the calculation settings and methods mentioned by Kao et al [10], and compares the calculation results on the propeller performance and resistance estimation with the experimental values to determine the correctness of the self-propulsion simulation
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