A systematic experimental approach to cavitation noise prediction of marine propellers

PhD ThesisMinimization of propeller cavitation noise is best achieved through accurate and reliable pre-dictions at an early design stage. The effect of cavitation and particularly the dynamics of cav-itation on URN is rather complex to understand and the current state of the art does not offer a plausible cavitation noise prediction method which can be implemented within the propeller design spiral. Within this framework, the aim of the present thesis is to enhance the understand-ing of the propeller cavitation noise by conducting detailed systematic cavitation tunnel tests to investigate the main propeller design parameters and operating conditions and to scrutinize their impact on propeller Radiated Noise Levels (RNL). The resulting experimental data are also utilized to compile a database that enables engineering a novel noise prediction method to be developed and used at preliminary design stage, using standard series approach. A holistic approach to cavitation noise has been adopted through experimental investigations into oblique flow effects on propeller noise and by conducting full scale and model scale noise experiments of a research vessel. These have been used to evaluate the capabilities of the adopted standard series based experimental prediction methodology. The accumulated knowledge based on prior experiments has been utilized to design standard series propeller test campaign. Experiments using members of Meridian standard propeller se-ries were tested both in an open water condition and also behind systematically varied wake inflows. Initially, a small subset of the Meridian standard propeller series was chosen, with loading conditions derived from in-service, ocean-going vessels. The resulting measured noise data were extrapolated to full-scale based on the powering information of these vessels to com-pare with average shipping noise data. Finally, a larger subset of the propeller series was tested systematically to compile a database of propeller cavitation noise and for the development of noise prediction software

Time accurate numerical cavitation erosion prediction of multiphase flow through a venturi

Cavitation erosion affects the efficient operation of the vessel’s propeller, leading to increased costs of operation and maintenance. Traditionally, erosion is predicted using dedicated cavitation tests with utilization of soft paint application or materials as erosive sensors. However, even with materials that are most susceptible to erosion, such tests constitute significant amount of time. It is well-known that cavitation erosion occurs with the impact of high velocity liquid jets generated by the imploding bubbles, also called water hammer effect, and induced shock waves over time. However, it is both not a viable approach to simulate the complete duration of an experiment using numerical methods and extremely expensive in terms of computational time. Therefore, it is a common simplification to assume cavitation events to be repetitive for numerical simulations and based on this assumption there has been a plethora of studies utilizing the numerical simulations for cavitation erosion prediction. Whilst these simulations utilize instantaneous erosive power indicators for cavitation erosion estimation, an approach that takes into account of the summation/accumulation of the erosive intensity over time for precise erosion threshold determination is non-existent. Within this framework this study presents a time accurate numerical cavitation erosion prediction based on the intriguing experimental study conducted by Petkovšek & Dular (2013) that achieved visual cavitation erosion within 1.5 seconds. In addition to the well-known erosive indicators such as Erosive Power Function (Eskilsson & Bensow, 2015), Gray Level Method (Dular et al., 2006) and Intensity Function Method (van Terwisga et al., 2009), in house functions developed by Lloyds Register (LR) Technical Investigation Department (TID) (Ponkratov, 2015; Ponkratov & Caldas, 2015) are used to compare against the experimental results. Comparisons both aided the determination of a time accurate threshold and utilized as an evaluation case for each erosive indicator

Systematic cavitation tunnel tests of a propeller in uniform and inclined flow conditions as part of a round robin test campaign

The effect of shaft inclination can induce important unsteady hydrodynamic phenomenon usually associated with small and high-speed craft. This paper presents systematic cavitation tunnel tests with a 214 mm diameter model propeller of a catamaran research vessel. The propeller is subjected to uniform and inclined flow conditions, to investigate its efficiency, cavitation and underwater radiated noise characteristics. The experiments were conducted in the Emerson Cavitation Tunnel of Newcastle Uni- versity based on the starboard 5-bladed right-hand propeller of the University's research vessel, The Princess Royal. In the paper the details of the tests and significant findings for the effect of the shaft inclination on the propeller efficiency, cavitation and underwater radiated noise characteristics are presented. A better understanding is sought in relation to the noise signatures of different types of cavitation. The systematic tests presented in the paper also have a long-term objective, being the first of an organised round robin test campaign that is being currently undertaken by the members of the Underwater Noise Community of Practice (CoP) of Hydro-Testing Forum (HTF). This long-term objective is to repeat similar tests in the different facilities of all CoP members to reveal the relative merits of their testing facilities for underwater noise investigations

Cavitation observations and noise measurements of horizontal axis tidal turbines with biomimetic blade leading-edge designs

This paper focuses on the study of cavitation and underwater noise performance of a biomimetically improved horizontal axis tidal turbine (HATT) with a leading edge design inspired by the tubercles on the pectoral fins of humpback whales. Systematic model tests were recently conducted and details of this test campaign together with the findings are summarised in the paper. Several full-scale tidal turbine application cases were studied to understand the full-scale operating conditions considering the characteristics of varied kinds of tidal energy devices, the varying wave height and the flood/ebb tide. A systematic test regime was then designed and conducted. A set of tidal turbines with different leading-edge profiles was manufactured and tested under different loading and hence cavitation conditions. During the tests, cavitation was observed and underwater noise level was measured in comparison with the cavitation and noise performance of a counterpart HATT without tubercles. The tested turbines displayed two main types of cavitation patterns independent of the tubercles. These were steady tip vortex cavitation and relatively intermittent cloud cavitation with a misty appearance. The leading-edge tubercles triggered the cavitation onset earlier for the tidal turbine but constrained the cavitation region to the trough between tubercles with a lesser extent on the blades. The noise performance was strongly related to the blade cavitation hence it was influenced by the leading-edge tubercles. While the turbine was working under the non-cavitating conditions the total noise level was similar to the background noise level. With the increase of the tip speed ratio the noise level was increased, while increasing blade pitch angle reduced the noise level due to lower blade loading. Cavitation inception and noise diagrams are provided as a database for future studies

Shelter models for consequence and risk assessment of CO2 pipelines

Pipelines are acknowledged as one of the most efficient and cost-effective methods for transporting large volumes of various fluids over long distances and therefore the majority of proposed schemes for Carbon Capture and Storage (CCS) involve high pressure pipelines transporting carbon dioxide (CO2). In order to be able to design and route pipelines safely, it is a code requirement that a separation distance, or safety zone, is defined between the pipeline and any habitable dwellings along the route. Safety zones are generally defined on the basis of a Quantitative Risk Assessment (QRA). The purpose of a QRA is to assess the risks posed by a pipeline failure to people in the vicinity and to ensure that consistent levels of risk are applied along the pipeline route. The risk levels are normally calculated along a transect drawn perpendicular to the pipeline. These levels are then compared with defined acceptance criteria to determine the safety zone i.e. the distance from the pipeline within which the risk to the public from a pipeline failure is considered to be unacceptable. The calculation of the risk level requires the determination of both the probability of a failure occurring in the pipeline and the consequences of that failure to the population. For natural gas pipelines, existing and accepted QRA techniques can be implemented to define the consequences of failure based on the thermal hazards. However for CO2 pipelines, the consequences of failure need to be considered differently, as they relate to a toxic hazard rather than a thermal hazard. Therefore in order to conduct a consequence analysis, what is required is a determination of the concentration of CO2 to which an individual may be exposed during a release event. This type of data can be generated either using dispersion models. These models will produce a profile of the change in CO2 concentration with time at various distances from the release, see for example [1, 2], that can then be used in the QRA to determine the toxic dose and therefore the level of harm experienced by an individual. However, none of these approaches consider the effect of shelter on the dose experienced by an individual who is within a building at the time of the release or is outside and enters a building to seek shelter. The work described in this paper seeks to address this gap and describes the application of two models ̶ an analytical and a Computational Fluid Dynamics (CFD) model ̶ that can be used to determine the effects of shelter on the toxic dose received by an individual during a pipeline release event. The motivation behind this work was: i) to develop a validated and computationally efficient shelter model, which had been tested against experimental data and CFD models, ii) to use both CFD and analytical models to demonstrate how shelter should be considered as part of the QRA procedure for a CO2 pipeline. A description of the analytical model has been published previously [3]. Therefore, the current paper concentrates on an explanation of the development and application of the CFD model. Using a case study scenario for a single roomed building, engulfed by a transient cloud of CO2, comparisons are made between the output of the analytical models and the CFD models for the same scenario. A sensitivity analysis indicates the input parameters that most affect the resultant toxic effects within the building. The paper further demonstrates how both models can be extended to investigate the effects of partial coverage of the building with the cloud of CO2 and the impact of partitions within the building. Predictions of toxic dose are made for both models and it is demonstrated how these results can be used in a QRA analysis. This work has been funded by the UK Carbon Capture and Research Centre within the framework of the S-Cape project (Shelter and Escape in the Event of a Release of CO2 from CCS Transport Infrastructure UKCCSRC-C2-179). References [1] M. Molag, C. Dam, Modelling of accidental releases from a high pressure CO2 pipelines, in:  10th International Conference on Greenhouse Gas Control Technologies, Amsterdam, 2011, pp. 2301-2307. [2] J. Koornneef, M. Spruijt, M. Molag, A. Ramírez, W. Turkenburg, A. Faaij, Quantitative risk assessment of CO2 transport by pipelines - A review of uncertainties and their impacts, Journal of Hazardous Materials, 177 (2010) 12-27. [3] C.J.Lyons, J.M.Race, H.F.Hopkins, P Cleaver, Prediction of the consequences of a CO2 pipeline release on building occupants. in Hazards 25: Edinburgh International Conference Centre, Edinburgh; United Kingdom; 13 May 2015 through 15 May 2015. vol. 160, Institution of Chemical Engineers Symposium Series, Red Hook, Hazards 25, Edinburgh, 201

Hydropod : an on-board deployed acoustic-visual device for propeller cavitation and noise investigations

Conducting noise trials with big merchant vessels could constitute serious economic and time losses for the ship operators. This study aims to introduce an experimental acoustic–visual device enabling economical and cost-effective noise trials in full scale. Noise emission and dynamics of propeller cavitation are investigated on a research vessel equipped with a customized submerged device called “Hydropod” that consists of hydrophones and a high definition, wide-angle underwater camera. Previously conducted noise trials following the international standards with an off-board hydrophone array are utilized for the validation of the adopted approach. The comparisons between the Hydropod measurements and conventional noise trial measurement results have shown promising correlations, except for a self-noise hump present in the noise spectra of the Hydropod measurements. Furthermore, by taking advantage of the replacement of the conventional propellers of the catamaran with a set of new profile technology (NPT) propellers, additional trials were conducted using the Hydropod. This enabled interpretation of the relative performance of both sets of propellers in terms of acoustics and cavitation extent. The NPT propellers were superior compared to the conventional propellers over the cavitation extent and resulting acoustic emissions

Underwater radiated noise characteristic of the hydro-spinna tidal turbine under induced cavitation

Over the past decade, the development of marine current turbines has progressed rapidly with prototypes and fullscale devices being deployed in the actual environment. With research focusing on the hydrodynamic and design aspects of the technologies used, little is known of the impact of marine current turbine operation on marine life and the environment. This paper looks at the Underwater Radiated Noise (URN) produced from the operation of the Hydro-Spinna turbine which is a horizontal-axis type concept design under development at Newcastle University. URN measurements were taken from a 280 mm diameter Hydro-Spinna model. The URN measurement was part of a comprehensive investigation conducted on the turbine model, where the local pressure in the tunnel was reduced to induce cavitation to study its characteristics. The noise data was found to correspond to the cavitation observation where the noise increases as more cavitation developed. In addition, only tip vortex cavitation was observed during the investigation indicating that this is the only cavitation characteristic of the Hydro-Spinna turbine. As more tip vortex cavitation was observed, the URN results exhibit an apparent trend, whereby the sound pressure level (SPL) increased and the frequency shifted towards the lower frequency region

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

Numerical optimization and experimental validation for a tidal turbine blade with leading-edge tubercles

Recently the leading-edge tubercles on the pectoral fins of humpback whales have attracted the attention of researchers who wish to exploit this feature in the design of turbine blades to improve the blade performance. The main objective of this paper is therefore to make a further investigation into this biomimetic design inspiration through a fundamental research study involving a hydrofoil section, which represents a straightened tidal turbine blade, with and without the leading-edge tubercles, using computational and experimental methods. Firstly a computational study was conducted to optimise the design of the leading-edge tubercles by using commercial CFD code, ANSYS-CFX. Based on this study the optimum tubercle configuration for a tidal turbine blade with S814 foil cross-section was obtained and investigated further. A 3D hydrofoil model, which represented a "straightened" tidal turbine blade, was manufactured and tested in the Emerson Cavitation Tunnel of Newcastle University to investigate the effect of various tubercle options on the lift and drag characteristics of the hydrofoil. The experiments involved taking force measurements using a 3-component balance device and flow visualisation using a Particle Image Velocimetry (PIV) system. These tests revealed that the leading-edge tubercles may have significant benefits on the hydrodynamic performance of the hydrofoil in terms of an improved lift-to-drag ratio performance as well as reducing the tip vortex which is main cause of the undesirable end-effect of 3D foils. The study explores further potential benefits of the application of leading-edge tubercles on tidal turbine blades

Full-scale unsteady RANSE CFD seakeeping simulations of a high-speed craft

This paper presents a series of RANSE-based seakeeping simulations on a 17m high-speed monohull. The study is performed on the Severn Class all-weather search and rescue lifeboat, designed and operated by the Royal National Lifeboat Institution (RNLI). The Severn is a planing craft with a maximum operational speed of 25 knots, although it often operates at semi-planing and displacement speeds in different situations and weather conditions