Experimental characterization of two CP propellers at different pitch settings, considering cavitating behaviour and related noise phenomena

Propeller design has evolved significantly in last years, with the introduction of numerical methods which can provide a very reliable assessment of propeller characteristics, not only in correspondence to the usual design conditions, but also to off-design conditions. Nevertheless, problems still exist if \u201cvery off-design conditions\u201d are considered, and if interest is posed on cavitation related problems such as radiated noise. Interest in radiated noise phenomenon is constantly increasing, not involving anymore only naval vessels, but affecting also design of other \u201chigh added value ships\u201d, such as cruise ships and megayachts, for which comfort problem and environmental impact are a key element. One of the most significant problems related to radiated noise, is the rather low amount of experimental data available, and this is particularly significant for CPP propellers at off design conditions. In present paper, the experimental characterization of two alternative designs of a CP propeller in terms of usual mechanical characteristic, cavitation and radiated noise is presented. Experimental campaign has been conducted considering two very different pitch settings, allowing to analyse propeller behaviour also in correspondence to very off design conditions

Dynamic simulation of a COGAS ship propulsion plant

In a previous paper the authors presented a comparison between a COGAS plant specifically designed and the original prime mover (a two stroke diesel engine) used for the propulsion of a large container ship. The comparison showed some advantages of the COGAS solution from both technical and commercial points of view, advantages that could become more evident, in a near future, also from an economic point of view, because of the adoption of increasingly stringent emission regulations in the shipping sector. A feasibility study of the COGAS solution requires the availability of numerical models not only for the propulsion system design and performance evaluation in steady state operation, but also for the dynamic simulation of its behavior in every off-design and transient condition. The last feature is important for the development of the propulsion control system. The paper presents a COGAS plant dynamic simulator, putting into evidence in particular detail the model of the heat recovery steam generator, the most critical component as regards transient situations. For the mentioned container vessel the prime mover dynamic analysis is combined with the overall propulsion system simulation, allowing to obtain some significant results relative to acceleration and deceleration maneuvers of the ship

Additive Manufacturing Application to a Ship Propeller Model for Experimental Activity in the Cavitation Tunnel

Additive manufacturing (AM), or three dimensional printing, is a modern way to build objects with possibly a high degree of accuracy and favorable cost/benefit ratio. This approach is widely used by many manufacturing industries and a certain interest for this innovative production technology is also growing in the ship design and production field. To this regard, the experimental activity at the model scale is often necessary for the ship performance assessment in the design phase. In the article, preliminary results of a propeller model for the cavitation tunnel, built with additive technology, are presented, showing the strengths and weaknesses of the printed model. Moreover, as an introductive overview, different AM technologies are briefly described, with the aim to point out potential applicability to ships

Numerical and Experimental characterization of a CP propeller unsteady cavitation at different pitch settings

Paper presents results obtained in a study dedicated to the experimental and numerical investigation of the steady and unsteady hydrodynamic characteristics of a modern CP propeller including off-design operating conditions, i.e. with the blade oriented at a pitch rather far from the design value. The extensive experimental campaign has offered the opportunity to validate the accuracy of two different CFD methods: a first order unsteady panel method with some non linearities (in the Kutta condition and flow adapted wake); and a state of the art RANSE solver, Also the unsteady conditions of the CP propeller are investigated at two very different pitch settings, The comparison of numerical predictions with experimental results shows a very good agreement of both the numerical methods with the experiments at design pitch, also with regards to cavitation predictions. On the contrary, results at highly reduced pitch show the limits of the conventional panel method, based on potential flow solution, for which the usual viscous corrections are not any more sufficient to cope with separated viscous flow of some blade sections, which are satisfactorily modeled by the RANSE solver, instead. From a careful comparison of the flow characteristics predicted by the two different numerical methods, some hypothesis for future enhancement of the panel method are formulated in the conclusions

Experimental Analysis of Cavitation Erosion on Blade Root of Variable Pitch Propeller

The aim of this study is to experimentally investigate the cavitation erosion on the blade root of a model scale controllable pitch propeller. Tests are carried out in a cavitation tunnel, using the soft paint technique to study cavitation erosion, exploiting also two standard cameras and one high speed camera to study the damage patterns and cavitation dynamics, respectively. Standard cameras are placed on the top of test section in order to periodically monitor the occurrence of damages on the layer of paint. The high-speed camera has been used instead to analyse bubble dynamics and identify potentially erosive phenomena. Three different cavitation bubble structures on the blade root have been identified in the present study: streak cavitation, spherical bubble cavitation, and twisting bubble cavitation. The paint tests results have been analysed together with high-speed videos, showing a remarkable agreement between the occurrence of damage and cavitation collapse phenomena. The results demonstrated two regions on the propeller blade root with high risk of erosion: (1) suction side blade root showed significant damage pattern due to single bubble as well as bubble assembly collapse, and (2) pressure side blade root showed slight damage pattern due to spherical bubble collapse

CPP propeller cavitation and noise optimization at different pitches with panel code and validation by cavitation tunnel measurements

The propeller design is an activity which nowadays presents ever increasing challenges to the designer, involving not only the usual mechanical characteristics fulfillment and cavitation erosion avoidance, but also other cavitation side effects, such as radiated noise and/or pressure pulses. Moreover, in some cases propeller characteristics have to be optimized in correspondence to very different functioning points, including considerably off-design conditions, hardly captured by conventional design methods. In the present paper, a recently presented method, based on the coupling between a multiobjective optimization algorithm and a panel code, is applied to the design of a CPP propeller at different pitch settings, with the aim of reducing the cavitating phenomena and, consequently, the resultant radiated noise. Particular attention has been devoted to the slow speed (low pitch) condition, obtained at constant RPM, and characterized by considerable radiated noise and vibrations related to face cavitation. Numerical results are validated by means of an experimental campaign, testing both the original and the optimized geometry in terms of cavitation extent and radiated noise. Experimental results confirm the numerical predictions, attesting the capability of the method to assess propeller functioning characteristics, thus representing a very useful tool for the designer in correspondence of challenging problems. \ua9 2012 Elsevier Ltd. All rights reserved

Extensive Cavitation Tunnel Acoustic Characterization of Controllable Pitch Propellers

Experimental tests in model-scale are the currently established (and more reliable) methods for the propeller acoustic characterization. However, they are affected by uncertainties mostly due to scale effects, which make it difficult to consistently reproduce in model-scale some of full-scale functioning conditions. In order to cope with this issue, it is interesting to define empirical formulations to shape the most significant cavitating phenomena in terms of URN spectrum. A suitable approach for the determination of such formulations may consist in the experimental characterization of model propellers collecting a large amount of data such to accurately describe propeller functioning conditions and related noise emissions. Collected data should be then analysed to extrapolate desired formulations exploiting advanced data analysis techniques. In the present work the acoustical characterization of two propellers, performed at the University of Genoa cavitation tunnel, is presented. The collected sample includes cavitation buckets with inception points of different phenomena, noise spectra, pressure pulses and photos picked up at various pitches and functioning points, including off design conditions

EFD and CFD characterization of a CLT propeller

In the present paper an experimental and numerical analysis of an unconventional CLT propeller is carried out. Two different numerical approaches, a potential panel method and an RANSE solver, are employed. Cavitation tunnel experiments are carried out in order to measure, as usual, thrust, torque, and cavity extension for different propeller working points. Moreover, LDV measurements are performed to have a deep insight into the complex wake behind the propeller and to analyze the dynamics of generated tip vortexes. The numerical/experimental analysis and comparison of results highlight the peculiarities of this kind of propellers, the possibility to increase efficiency and reduce cavitation risk, in order to exploit the design approaches already well proven for conventional propellers also in the case of these unconventional geometries

COGAS Plant as Possible Future Alternative to the Diesel Engine for the Propulsion of Large Ships\u2019

none4G. BENVENUTO; BERTETTA D; CAROLLO F; CAMPORA U.Benvenuto, GIOVANNI BATTISTA; Bertetta, D; Carollo, F; Campora, Ug