Numerical assessment of the effect of length, angle of attack, and type of ducts on hydrodynamic parameters of a linear-jet propulsion system

Abstract

Achieving noble and more practical propulsion systems is still a major concern for engineers and researchers. Accordingly, many researchers have strived to opt for better and suitable system for the targeted vessels. One of the marine propulsion systems is linear-jet propulsion which includes rotor and stator. In this paper, the effects of geometrical shape of the duct in the form of different length and angle of attack for two types of the accelerating and decelerating ducts are comprehensively explored. Furthermore, section of rotor from Kaplan series are selected and the geometrical shape effects of the rotor on hydrodynamic performance of linear-jet propulsion system are also investigated. Therefore, to obtain the effects of the expressed parameters on the hydrodynamic characteristics of this propulsion system, Ansys-CFX software has been used. The governing equations of the studied problem are RANS equations and SST k-omega turbulent model is utilized. The obtained results are presented in the form of dimensionless coefficients of the forces applied on the propulsion system. The existing data for a ducted propeller are used to validate the numerical solution. Based on the results of the numerical solution, it is concluded that use of a decelerating duct increases the efficiency of the linear-jet system. On the other hand, the use of accelerating ducts reduces the hydrodynamic efficiency of the linear jet, so the performance is not desirable at high advance ratio. Therefore, the use of decelerating ducts in the linear-jet system is found to be the appropriate choice. Results further illustrate that, if the duct length increases, the generated thrust by the rotor increases. It is also concluded that, by increasing the angle of attack of the decelerating duct, the overall efficiency of the linear-jet propulsion system decreases.