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Modern warships are designed with built in stealth features to avoid detection by adversaries. Acoustic stealth is one of the most important aspects to meet this requirement of warships. To achieve acoustic stealth, underwater radiated noise is to be minimized to the extent possible. Two major sources of underwater radiated noise are machinery and propeller. Thus it is implied that suitable methods are to be adopted for control of machinery and propeller noise. While literature reveals that several methods were effectively developed for control of these noises, a lot of research is still being carried out by various researchers on newer techniques and improvisations of existing approaches. Machinery noise is controlled by reducing vibration at source and through structural path treatments such as isolation and damping. Propeller noise can be controlled by reducing pressure oscillations apart from other methods. Different parameters affect pressure oscillations, i.e. change in Skew Angle, number of blades, blade area, and Suitable distribution of blade pitch, Trailing edge geometrical modifications and propeller blade finish. Aim of the work presented in this paper is to control propeller noise by changing its geometry. In this work, noise was investigated by varying blade thickness of 5 and 6 bladed marine propellers. Numerical simulation of a chosen propeller was resorted to for prediction of unsteady non cavitating propeller noise. The approach involved solid modeling of the propeller followed by CFD modeling including water domain around the propeller. Pressure fluctuations predicted through CFD analysis were used for acoustic analysis employing FWH method and eddy viscosity model of Large Eddy Simulation. Pressure based, unsteady implicit formulation of second order was chosen as solver. Noise spectrum predicted over the frequency range of 0-10 kHz. Noise was predicted for blade thickness increments of 0.1mm to 0.5mm at specified operating conditions of propeller speed. From the results it is observed that increase in blade thickness leads to reduced noise and among the studied configurations, 6 bladed propellers with 0.5mm blade thickness increment generates lowest noise. While designing marine propeller for low noise, it is also important to ensure that it satisfies hydrodynamic performance requirements. Hence, in this study hydrodynamic performance parameters such as thrust and torque were checked for the low noise propeller configuration and it was found to be better than base line propeller.
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