Analysis of Propeller Wake Field for Twisted Rudder Design

Propeller boss cap fins (PBCF) is one of the most popular ESDs in the industry. The present study aims to investigate effects of design variations of PBCFs on the propulsive efficiency and propeller wake field, with special attention on hub vortex dynamics. The wake fields and force on the whole propulsive system were measured by a towed underwater stereoscopic particle image velocimetry (SPIV) system and a propeller open water (POW) test dynamometer, respectively. Design parameters of PBCFs, i.e., the fin surface area and the angle of attack onto the fins, were varied to control fin loading on the PBCF. In the wake field, root vortices generated from the propeller blades were separated by PBCF and did not form a strong hub vortex, which caused pressure drop on the propeller boss cap. The hub vortex reduction practically increased total thrust, as evidenced in the global force measurement results. In PBCF design variations, Total efficiency increased linearly as the pitch angle and fin chord length decreased. The global force measurement results implied that PBCF in light loading separated root vortices efficiently. Hub vortex reduction by PBCF in light loading was also confirmed by the wake field measurement. In the case of low fin height, however, root vortices were not blocked and actually merged to form a hub vortex. Therefore, the primary function of PBCF, i.e., reducing hub vortex, was not effective anymore and the total efficiency decreased. In heavy loading conditions, axial velocity near the center retarded further, causing greater drag and diminishing the total efficiency. The model tests were also conducted in self propulsion condition, to reveal that the new PBCF with reduced loading also improves the energy saving performance when it works in the wake of the ship.

Download Full-text

Numerical Prediction of Thruster-Thruster Interaction

Volume 4: Ocean Engineering; Ocean Renewable Energy; Ocean Space Utilization, Parts A and B ◽

10.1115/omae2009-79744 ◽

2009 ◽

Author(s):

R. Bosland ◽

J. M. Dijk ◽

R. H. M. Huijsmans

Keyword(s):

Flow Field ◽

Interaction Model ◽

Turbulent Jet ◽

Linear Potential ◽

Wake Field ◽

Vortex Model ◽

Propeller Wake ◽

Numerical Instabilities ◽

Wake Model ◽

Set Up

Many vessels deploying offshore activities nowadays are dynamically positioned by multiple azimuth thrusters instead of anchors. The multiple propulsor set up, gives a considerable flexibility to work fast and accurate. Due to the fact that the thrusters are positioned relative close to one another their performance is influenced. Normally to quantify this influence and take into account in the DP control algorithm, elaborate experiments have to be performed. To optimize the results a robust numerical flow solver is developed to predict the interaction effects. The program is used to optimize the effort put into these experiments. The developed propeller interaction model is a first order potential based panel method, which uses zero order doublets and sources panel elements. This method is selected to prove the main objective of this research that; Although the slipstream of a thruster has a very turbulent character the interaction can be modeled without taking the viscosity into account as long as an accurate distorted flow field behind a propeller can be predicted. At the 2nd thruster the distorted flow field due to the 1st thruster is modeled by means of two wake field models; a linear potential wake model and an empirical turbulent jet model. Due to the intersection of wake and body panels at the 2nd thruster, numerical instabilities occur at the collocation points. These instabilities are removed by applying a realistic vortex model instead of the analytic vortex model which has infinite velocities in the core. The second problem is to capture the divergent and subsiding character of a propeller wake field by means of a linear potential wake model. This problem is resolved by validating the region for which the results are still accurate. From the results it is concluded that the thruster interaction propeller model coupled to the turbulent jet wake field yield accurate thruster interaction results. For the linear potential wake field results are promising but adaptations are needed to improve the prediction of the divergent and subsiding character of the physical wake field.

Download Full-text

Wake optimization of ducted propeller

TRANSACTIONS OF THE KRYLOV STATE RESEARCH CENTRE ◽

10.24937/2542-2324-2021-1-395-79-84 ◽

2021 ◽

Vol 1 (395) ◽

pp. 79-84

Author(s):

V. Bushkovsky ◽

◽

A. Koval ◽

A. Maslova ◽

◽

...

Keyword(s):

Performance Parameters ◽

Unsteady Forces ◽

Wake Field ◽

Propeller Wake ◽

Ducted Propeller ◽

Unsteady Force ◽

Target Performance ◽

Methods Analytical ◽

Propeller Geometry ◽

Effective Wake

Object and purpose of research. This paper discusses marine ducted propeller and the ways to ensure its target performance parameters. The purpose of this study was to mitigate unsteady forces on the propeller behind the duct struts. Materials and methods. Analytical estimates of propeller parameters and in-house KSRC methods for numerical simulation of ducted propeller behaviour. Main results. Calculations of effective wake behind duct struts taking into account the flow around hull and its append-ages. Calculations of unsteady forces for a standard propeller operating in this wake. Design of a propeller with increased blade skew. Calculations of unsteady forces for the new propeller in the initial wake. Wake field parameters contributing to mitigation of unsteady forces. Calculations for the new strut shape for wake optimization. Calculations of unsteady force amplitudes for standard propeller in the new wake. Conclusion. Ducted propeller discussed in this study was meant to illustrate how propeller wake properties, like unsteady forces, can be optimized without changing propeller geometry, only by means of curved duct struts.

Download Full-text

Experimental Investigation of propeller Wake Velocity Field for the Major Factors Affecting Propeller Wake Wash

10.20944/preprints201804.0004.v1 ◽

2018 ◽

Author(s):

Md. Asif Amin ◽

Bruce Colbourne ◽

Brian Veitch

Keyword(s):

Velocity Field ◽

Axial Velocity ◽

Significant Component ◽

Factors Affecting ◽

Wake Field ◽

Propeller Wake ◽

Axial Velocity Distribution ◽

The Mean ◽

Major Factors ◽

Effective Wake

The propeller jet from a ship has a significant component directed upwards towards the free surface of the water, which can be used for ice management. This paper describes a comprehensive laboratory experiment where the influences of operational factors affecting a propeller wake velocity field were investigated. The experiment was done on a steady wake field to investigate the characteristics of the axial velocity of the fluid in the wake and the corresponding variability downstream of the propeller. The axial velocities and the variability recorded were time-averaged. Propeller rotational speed was found to be the most significant factor, followed by propeller inclination. The experimental results also provide some idea about the change of the patterns of the mean axial velocity distribution against the factors considered for the test throughout the effective wake field, as well as the relationships to predict the axial velocity for known factors.

Download Full-text

Analysis of propeller wake field and vortical structures using k−ω SST Method

Ocean Engineering ◽

10.1016/j.oceaneng.2020.107247 ◽

2020 ◽

Vol 204 ◽

pp. 107247 ◽

Cited By ~ 3

Author(s):

Morteza Heydari ◽

Hamid Sadat-Hosseini

Keyword(s):

Vortical Structures ◽

Wake Field ◽

Propeller Wake

Download Full-text

Sound Field Properties of Non-Cavitating Marine Propellers

Journal of Marine Science and Engineering ◽

10.3390/jmse8110885 ◽

2020 ◽

Vol 8 (11) ◽

pp. 885

Author(s):

Youjiang Wang ◽

Ulf Göttsche ◽

Moustafa Abdel-Maksoud

Keyword(s):

Sound Field ◽

Permeable Surface ◽

Ship Wake ◽

Wake Field ◽

Marine Propellers ◽

Propeller Wake ◽

Surface Dimension ◽

First Time ◽

Inflow Conditions ◽

Method Approach

The sound field properties of non-cavitating marine propellers are investigated using a hybrid method, in which the FWH (Ffowcs William-Hawkings) analogy is coupled with the BEM (Boundary Element Method) approach. The investigations include both the uniform and non-uniform inflow conditions. For both conditions, the dominant sound source terms and the decay rate of the noise with regard to the distance to propeller centre are investigated. The influence of the permeable surface dimensions in the permeable FWH approach on the hydroacoustic result is also investigated. To carry out the investigations, the formulation to calculate acoustic pressure generated by the propeller wake sheet is proposed for the first time. The issues associated to coupling permeable FWH approach and BEM are also discussed, including the fictitious volume flux problem and the consideration of the ship wake field. It was found that the influence of the permeable surface dimension is little for the 1st BPF (Blade Passage Frequency), but cannot be ignored for the 3rd BPF. In the uniform inflow situation the thickness terms are found to be dominant, while in the non-uniform inflow situation the loading terms are dominant.

Download Full-text

Experimental Study on Dynamic Structure of Propeller Tip Vortex

Polish Maritime Research ◽

10.2478/pomr-2020-0022 ◽

2020 ◽

Vol 27 (2) ◽

pp. 11-18

Author(s):

Li Guangnian ◽

Qingren Chen ◽

Yue Liu

Keyword(s):

Dynamic Structure ◽

Tip Vortex ◽

Fluctuating Pressure ◽

Tip Vortex Cavitation ◽

Wake Field ◽

Propeller Wake ◽

Propeller Design ◽

Piv Technique ◽

Principal Source ◽

Blade Tip

AbstractPropeller cavitation is a main source of fluctuating pressure and noise induced by propellers, and the tip vortex cavitation is the principal source. The present study measures the flow fields near the blade tip using the 2D-PIV technique. The experimental setup and scheme are introduced. We monitor the process of generation and shedding of the propeller tip vortex in real time and analyse the dynamic structure of the tip vortex by testing the propeller wake field under different phases of the axial plane. The distribution characteristics of radial and axial velocity are also analysed. The influence range and the vorticity of the tip vortex and trailing vortex are obtained. All of the measured quantitative data are useful for future propeller design.

Download Full-text