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Cavitation of a Propeller and Influence of an Wake Equalizing Duct

Martinas G.

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

2015

Vol. 9, no. 2

235--241

The wake equalizing duct (WED) is one of the most commonly used energy saving devices for improving the propulsion performance of a ship; and reducing the propeller-excited vibrations and viscous resistance forces. During the last three decades considerable research and development activities have taken into place within this context. Most of these devices are used to improve propulsive efficiency, but some of them aims to improve other performance characteristics, such as cavitations, vibration, noise, maneuverability, etc. Marine propellers are the most common propulsion systems; nevertheless, it is possible to improve its propulsive performance using additional auxiliary propulsor devices (unconventional propulsors). Two versions of an existing ship in normal version and fitted with WED device were analyzed in order to demonstrate the influence on the WED device on the propeller cavitations . It was determined that the values for the pressure coefficient is 1.98 for without WED situation and 2.029 for WED situation. The difference is not so significant that, the conclusion is that WED device did not have influence over the cavitations of the propeller. Either optimization of dimension and form of WED did not help in reducing negative effects of cavitations. Not being a study in this paperwork, to decrease the cavitations we have other choices including a sound design of the propeller biased to improve the propeller behavior in cavitations. WED is clearly not a choice.

Numerical simulation of tonal and broadband hydrodynamic noises of noncavitating underwater propeller

Kheradmand S., Rahrovi A., Mousavi B.

Polish Maritime Research

2014

nr 3

46--53

The objective of the study was to carry out numerical simulation of the hydrodynamic noise generated by the flow around a non-cavitating underwater propeller. To achieve this goal, hydrodynamic simulation of flow around the propeller was initially done. The unsteady 3-D flow was modelled numerically along with the LES turbulence model. The hydrodynamic parameters calculated for different advance coefficients are visibly in line with the previous experimental works. The turbulent quantities of the hydrodynamic study and the FWH model were used to find spectral distributions of flow noise for different advance coefficients. The results of the acoustic investigation were compared against other numerical results. An array of 100 hydrophones was used to find the directional distribution of the noise around the propeller. The obtained results indicate that, for different advance coefficients, the highest intensity of the noise recorded by different receivers around the propeller occurs in BPF. Furthermore, it has been found that the noise is directionally as well as intensively distributed around the propeller. Noise distributions of noise are presented and discussed for different regimes of propeller rotation. The analysis of the expanded spectrum (broadband analysis) of noise on the propellers has also been done and the contribution of all parts of the propeller to hydrodynamic noise generation are presented.