Experimental Analysis of the Near Wake from a Ducted Thruster at True and Near Bollard Pull Conditions Using Stereo Particle Image Velocimetry (SPIV)

Thrusters working at low advance coefficients are employed in a wide range of offshore and marine applications on Floating, Production, Storage, and Offloading (FPSO) systems;shuttle tankers; tug boats; and mobile offshore units. Therefore, an understanding of the flow around the thrusters is of great practical interest. Despite this interest, there is lack of knowledge in the description of the hydrodynamic characteristics of a ducted thruster\u27s wake at bollard pull and low advance coefficient values. This work was aimed at providing detailed data about the hydrodynamic characteristics of a Dynamic Positioning (DP) thruster near wake flow at different low advance coefficient values. Wake measurements were made during cavitation tunnel tests carried out on a ducted propeller model at the Italian Ship Model Basin (INSEAN), Rome, Italy. Through these experiments,th e DP thruster near wake velocity components at different downstream axial planes, up to 1.5 diameters downstream, were obtained using a Stereoscopic Particle Image Velocimetry (SPIV) system. These experiments were carried out at different advanceoefficient sJd values [bollard pull sJ=0d, J=0.4 and J=0.45]

Stereoscopic PIV aided wake simulation of a catamaran research vessel using a dummy-hull model in a medium size cavitation tunnel

The rising marine environmental concern has recently targeted underwater radiated noise. Amongst various sources present on-board, propeller cavitation noise is known to be the dominant source that may be harmful to marine biodiversity. To be able to minimize anthropogenic noise footprint, full-scale and model-scale test campaigns are the most reliable tools to measure or predict the noise sound pressure level. Within this framework, hydro-acoustic cavitation tunnel experiments carry utmost importance for model-scale tests. Due to limited space of the cavitation tunnel, a shortened dummy-hull is often used, even though the flow passing through the propeller plane of the dummy model does not represent a fully developed wake. This paper presents a wake simulation methodology for a shortened dummy-hull model of Newcastle University research vessel “The Princess Royal” with the aid of Stereoscopic Particle Image Velocimetry (SPIV) in Emerson Cavitation Tunnel. With such method, after three iterations sufficient similarity between target wake and simulated wake has been achieved. Adopted approach has been found to be significantly effective in terms of reducing the time and the iterations during wake simulation process

The Specialist Committee on Detailed Flow Measurements. Final Report and Recommendations to the 26th ITTC

The scope of this report is to review up-todate measurement systems and methods available for flow-field and wave-field measurements and describe applications of Particle Image Velocimetry (PIV), stereoscopic PIV (SPIV), Laser Doppler Velocimetry (LDV),Particle Tracking Velocimetry (PTV),holography, and other emergent methods, for the measurements of flow separation, wake,vortex strength, etc, for ship hydrodynamics problems. Furthermore, practical issues related to the application of these measurement techniques, especially PIV and SPIV, in largescale tow tank facilities and cavitation tunnels will be discussed, with recommendations for future work for the ITTC in these areas

Coherent and turbulent process analysis of the effects of a longitudinal vortex on boundary layer detachment on a {NACA0015} foil

In the present paper, interactions mechanism of the propeller hub vortex with the rudder installed in its wake are studied. This configuration corresponds to the field of marine propulsion allowing specific problem such as cavitation inception, modification of the propulsive performances and induced vibrations. To better understand the complex mechanisms due to the impact of the propeller-rudder interactions decided to put more emphasis onto configuration where the hub vortex is generated by an elliptical 3D foil and is located upstream the 2D NACA0015 foil at high incidences at Reynolds number 5 105. The physical mechanism involved in the interactions between a single longitudinal vortex and boundary layer detachment was studied using time resolved stereoscopic PIV techniques. Particular attention was paid to the detachment at 25° incidence and a detailed cartography of the mean and turbulent properties of the wake is proposed. The proper orthogonal decomposition (POD) analysis was applied in order to highlight the unsteady flow aspects using phase averaging based on the first POD coefficients to characterize the turbulent and coherent process in the near wake of the rudder

The Specialist Committee on Wake Fields Final Reports and Recommendations to the 25th ITTC

The recommended actions of 25th ITTC Specialist Committee on Wake-Fields, as stated above are focused on two main areas, the review of the numerical prediction and experimental measurement (methods) of wakefields and the review and development of ITTC procedures

Experimental investigations on the flow structure and turbulence of the propeller tip vortex at different cavitation states

In a previous series of open water tests for a certain marine propeller, we kept decreasing the advance coefficient and observed the propeller tip vortex going through a process from non-cavitating to cavitating and back to non-cavitating but micro-bubble-filled conditions. This process provides an excellent opportunity for investigating the flow structure and the turbulence associated with the tip vortex under different statuses of cavitation. Particle image velocimetry technique is used to measure the instantaneous velocity distributions at six experimental conditions parameterized with the advance coefficient and the cavitation number. The results show that the mean circulation (or mean kinetic energy) of either the cavitating or the micro-bubble-filled tip vortex is greater than that of the singlephase (liquid) counterpart, whereas the turbulent kinetic energy associated with the tip vortex has an opposite trend. These phenomena imply that extraordinary kinetic energy sources/transfers within the flow exist due to interactions between the vapor and the liquid phases of the tip vortex fluid.http://deepblue.lib.umich.edu/bitstream/2027.42/84224/1/CAV2009-final182.pd

Investigation of the flow field around a propeller-rudder configuration: on-surface pressure measurements and velocity-pressure-phase-locked correlations

The present paper deals with the problem of the propeller induced perturbation on the rudder . The study aims at providing insights on the key mechanisms governing the complex interaction between the propeller wake structures and the rudder. In this regard, a wide experimental activity that concerned PIV and LDV velocity measurements and wall-pressure-measurements on the two faces of the rudder was performed in a cavitation tunnel. The major flow features that distinguish the flow field around a rudder operating in the race of a propeller, were highlighted, such as the complex dynamics of the propeller tip votices and the re-storing mechanism of the tip vortex downstream of the rudder. Wall-pressure signals were Fourier decomposed and, then, reconstructed isolating the contributions of the more energetic harmonics when both the propeller phase and the rudder deflection change

Propeller tip and hub vortex dynamics in the interaction with a rudder

In the present paper, the interaction mechanisms of the vortices shed by a single-screw propeller with a rudder installed in its wake are addressed; in particular, following the works by Felli et al. (Exp Fluids 6(1):1-11, 2006a, Exp Fluids 46(1):147-1641, 2009a, Proceedings of the 8th international symposium on particle image velocimetry: Piv09, Melbourne, 2009b), the attention is focused on the analysis of the evolution, instability, breakdown and recovering mechanisms of the propeller tip and hub vortices during the interaction with the rudder. To investigate these mechanisms in detail, a wide experimental activity consisting in time-resolved visualizations, velocity measurements by particle image velocimetry (PIV) and laser Doppler velocimetry (LDV) along horizontal chordwise, vertical chordwise and transversal sections of the wake have been performed in the Cavitation Tunnel of the Italian Navy. Collected data allows to investigate the major flow features that distinguish the flow field around a rudder operating in the wake of a propeller, as, for example, the spiral breakdown of the vortex filaments, the rejoining mechanism of the tip vortices behind the rudder and the mechanisms governing the different spanwise misalignment of the vortex filaments in the pressure and suction sides of the appendage