Marine propeller hydrodynamic and hydroacoustic performance with roughness effects

Shipping noise is considered a primary contributor to anthropogenic noise in oceans. With an expansion of the world fleet, the Underwater Radiated Noise (URN) levels have increased considerably, especially in the low-frequency band of the noise spectrum. As marine animals generally use sound in the low-frequency region, URN has been a major factor adversely affecting marine life. This potential harmful impact of URN on marine fauna has been commonly investigated in many research projects using experimental methods since the prediction of URN using numerical methods are rather new research field in marine applications. Therefore, in recent years, the accurate prediction of propeller URN has become of great importance to obtain the acoustic signature of the vessel and apply further noise mitigation concepts. Although several research studies have recently been carried out to predict the propeller URN using numerical methods, the verification and validation studies are still rare. Thus, the validity of the current numerical methods, together with the acoustic analogies for the prediction of propeller URN, is not yet fully understood. Also, the research studies are generally conducted for the propellers in model scale operating under non-cavitating conditions. Although several studies have been for predicting cavitating propeller URN, these research studies are still limited to sheet cavitation modelling due to the modelling complexity of the tip vortex cavitation (TVC). Moreover, the influence of roughness applied on the propeller blades and hub on propeller hydrodynamic and hydroacoustic performance has not been explored yet using Computational Fluid Dynamics (CFD) methods. Based on the above background, this PhD thesis aims to develop a mathematical model to investigate the propeller hydrodynamic performance, including cavitation and hull pressure fluctuations, and propeller URN in the presence of roughness using advanced numerical modelling and developed meshing techniques. This aim has been accomplished by using the validated state-of-art CFD tools. In the thesis, firstly, the effects of grid resolution on the accurate prediction of propeller URN and the contribution of nonlinear noise sources on overall propeller URN under non-cavitating conditions were explored. Secondly, the newly developed Vorticity-based Adaptive Mesh Refinement (V-AMR) technique was developed for accurate solution of the tip vortex flow and hence better realisation of TVC in the propeller slipstream. The V-AMR technique was also utilised to include the contribution of TVC on overall propeller URN for both model and fullscale propellers. Then, comprehensive verification and validation study was conducted to explore the effectiveness of the developed CFD approach through the propeller hydrodynamic performance, cavitation extension, hull pressure fluctuations and propeller URN for model and full-scale propellers operating under uniform and non-uniform flow conditions. Finally, the influence of roughness applied on the propeller blades and hub on propeller hydrodynamic and hydroacoustic performance was investigated. The numerical investigations conducted with the developed CFD method in this thesis demonstrated the satisfactory capability and effectiveness of the method for predicting the propeller hydrodynamic performance, including cavitation extension, hull-pressure fluctuation and URN, combined with the acoustic analogy for the URN. Thus, similar to other ship hydrodynamic problems (e.g., ship resistance, propulsion), CFD can also be reliably used, particularly for predicting the propeller URN, under non-cavitating and cavitating conditions. Also, the application of a new meshing technique, V-AMR, can be a practical way to investigate the tip vortex flow, TVC and include its effects on propeller URN effectively. Finally, the roughness application can also be an attractive method for mitigating the cavitation and hence propeller URN, especially for retrofit applications.Shipping noise is considered a primary contributor to anthropogenic noise in oceans. With an expansion of the world fleet, the Underwater Radiated Noise (URN) levels have increased considerably, especially in the low-frequency band of the noise spectrum. As marine animals generally use sound in the low-frequency region, URN has been a major factor adversely affecting marine life. This potential harmful impact of URN on marine fauna has been commonly investigated in many research projects using experimental methods since the prediction of URN using numerical methods are rather new research field in marine applications. Therefore, in recent years, the accurate prediction of propeller URN has become of great importance to obtain the acoustic signature of the vessel and apply further noise mitigation concepts. Although several research studies have recently been carried out to predict the propeller URN using numerical methods, the verification and validation studies are still rare. Thus, the validity of the current numerical methods, together with the acoustic analogies for the prediction of propeller URN, is not yet fully understood. Also, the research studies are generally conducted for the propellers in model scale operating under non-cavitating conditions. Although several studies have been for predicting cavitating propeller URN, these research studies are still limited to sheet cavitation modelling due to the modelling complexity of the tip vortex cavitation (TVC). Moreover, the influence of roughness applied on the propeller blades and hub on propeller hydrodynamic and hydroacoustic performance has not been explored yet using Computational Fluid Dynamics (CFD) methods. Based on the above background, this PhD thesis aims to develop a mathematical model to investigate the propeller hydrodynamic performance, including cavitation and hull pressure fluctuations, and propeller URN in the presence of roughness using advanced numerical modelling and developed meshing techniques. This aim has been accomplished by using the validated state-of-art CFD tools. In the thesis, firstly, the effects of grid resolution on the accurate prediction of propeller URN and the contribution of nonlinear noise sources on overall propeller URN under non-cavitating conditions were explored. Secondly, the newly developed Vorticity-based Adaptive Mesh Refinement (V-AMR) technique was developed for accurate solution of the tip vortex flow and hence better realisation of TVC in the propeller slipstream. The V-AMR technique was also utilised to include the contribution of TVC on overall propeller URN for both model and fullscale propellers. Then, comprehensive verification and validation study was conducted to explore the effectiveness of the developed CFD approach through the propeller hydrodynamic performance, cavitation extension, hull pressure fluctuations and propeller URN for model and full-scale propellers operating under uniform and non-uniform flow conditions. Finally, the influence of roughness applied on the propeller blades and hub on propeller hydrodynamic and hydroacoustic performance was investigated. The numerical investigations conducted with the developed CFD method in this thesis demonstrated the satisfactory capability and effectiveness of the method for predicting the propeller hydrodynamic performance, including cavitation extension, hull-pressure fluctuation and URN, combined with the acoustic analogy for the URN. Thus, similar to other ship hydrodynamic problems (e.g., ship resistance, propulsion), CFD can also be reliably used, particularly for predicting the propeller URN, under non-cavitating and cavitating conditions. Also, the application of a new meshing technique, V-AMR, can be a practical way to investigate the tip vortex flow, TVC and include its effects on propeller URN effectively. Finally, the roughness application can also be an attractive method for mitigating the cavitation and hence propeller URN, especially for retrofit applications