Eliche di Superficie: Stato dell'Arte

Conferenza Atena, Settembre 2007, Fiesso d'Artic

Nuove tecniche sperimentali per la caratterizzazione dei fenomeni cavitativi

Articolo su Rivista Tecnologie trasporto mare - n\ub02.2008 - ISSN 1721-758

Performance of a Family of Surface Piercing Propellers

Experimental tests have been performed on a systematic series of surface piercing propellers with varied number of blades (4 and 5) and pitch ratio (from 0.8 to 1.4). Influence of depth of immersion and shaft inclination is discussed and results for variations in these parameters are presented. Regression equations are given describing the relationship of the thrust and torque coefficients for advance coefficients above the critical values. Influence on Weber number is briefly considered, confirming results of previous works. This work is the result of a research on the performances of surface piercing propellers undertaken by the University of Genoa and was partly developed as a doctoral thesis

Surface Piercing Propellers for Displacing Vessels

Surface piercing propellers had several successful applications into the field of high-speed vessels; rarely, however, have been used for conventional dis-placing vessels, where they are also named \u201cPSP\u201d (Partially Submerged Pro-pellers). This paper deals with the application of a PSP on a new livestock carrier dis-placing about 5000 tons which has been successfully trading since 1998. After a brief introduction, where the state of the art is described, a few theo-retical issues are discussed, and short description of the research and design work is presented. The results of various other tests performed with PSP both with models and in full scale are also illustrated and briefly discussed; these have been then compared with those obtainable on conventional cases. Risks of possible undesired phenomena and benefits related to the applica-tion of PSP in large scale on displacing ships of different type and size are also dealt with and an outlook of investigations recently carried out on a peculiar application of PSP is also illustrated

Model Tests and full scale operation with surface piercing propellers

Surface piercing propellers have had several successful applications in field of high-speed vessels; rarely, however, have been used for conventional displacing vessels, where they are also known as Partially Submerged Propellers (PSPs). This paper deals with the application of a PSP on a new livestock carrier, displacing about 5000 t, which has been successfully trading since 1998. After a brief introduction, where the state-of-the-art is described, a few theoretical issues are discussed, and short description of the research and design work is presented. The results of various other tests performed with PSPs both with models and in full scale are also illustrated and briefly discussed; these have been then compared with results obtainable from conventional propeller installations. Risks of possible undesired phenomena and benefits related to the application of large scale PSPs on displacing ships of different types and sizes are also dealt with, and an overview of investigations recently carried out on a particular application of a PSP is illustrated

An Experimental and Numerical Study on Cavitation of Hull Appendages

In the present work a study on cavitation of hull appendages, such as stabilizer fins or rudders, is presented. The attention is focused on tip related cavitation and especially on tip vortex cavitation. Devices, such as end plates and tip fairing, commonly adopted to reduce this phenomenon are analyzed trough experiments and numerical calculations. Various solutions are compared underlining their advantages and shortcomings, considering the effect on cavitation inception and vortex intensity. With this aim, a model of control surface was fitted with different end plates and with a tip fairing and tested at various angles of attack. Experiments were carried out in the cavitation tunnel of the University of Genoa while CFD computations were performed by CETENA. Moreover a comparison between experiments and numerical results is presented showing the relation existing between the two different approaches. As a result a simplified technique to predict cavitation phenomenon by means of numerical simulations calibrated with experimental results is outlined

Development of an experimental device for a pod fitted with contra-rotating propellers

In present paper the development of a device for testing a pod fitted with contra-rotating propellers is presented. The device was realized in order to be mounted on the University of Genoa Cavitation Tunnel to investigate both global performances and cavitation phenomena. Although standard cavitation tunnels have in some cases the capability of testing contra-rotating propellers, the whole propulsive efficiency of the pod is rarely determined. This was one of the objectives of the developed device, designed in the framework of a research project in cooperation with Zf Marine, whose final aim is to develop a design procedure for contra-rotating propellers. One of the objectives of present study was the simplicity of the device, in order to minimise costs, searching for a compromise between testing accuracy and device complexity, as described in the paper. A first application of the testing equipment is then described, showing results obtained for a couple of propellers, which were tested alone and in contra-rotating configuration. Despite the practical problems which had to be overcome to keep the measuring system as simple as possible, results were rather satisfactory, allowing to measure usual propeller coefficients and to have an insight into the complex cavitating behaviour of this kind of propulsors