Interaction of parametrically designed low cavitated propeller and twisted rudder

Flow problems around objects are complex problems. These problems are solved using computational methods. The developing computer technology allows to verify expensive experiments using the finite element method. A certain part of the criteria in the design work of Naval Architecture is the field of hydrodynamics. Estimating the characteristics of the ship at the design stage that can be obtained by experimental analysis with the help of computational fluid dynamics (CFD) methods also contributes to the development of experimental methods. In ships, cavitation caused by the interaction of the propeller and rudder after a certain speed, reduces the hydrodynamic properties and working life of the propeller and rudder. In addition, cavitation is one of the main causes of vibration and noise in ships. The whole physics of cavitation cannot be revealed. Cavitation problems can be solved by utilizing numerical approaches. A cavitation flow solution can be made by making some assumptions and simplifications using the Computational Fluid Dynamics (CFD) method. Today, thanks to the rapidly developing technology, the transition of two-phase flow from the liquid phase to the vapor phase can be solved by modeling cavitation flow as a result of a bubble collapse using CFD analysis. The accuracy of the CFD method used in the study was obtained by comparing it with the current experimental results in the literature. The numerical analyses in the study were performed using the Reynolds Averaged Navier-Stokes (RANS) model in the Ansys CFX CFD software. The analyses were solved by using the simplified Rayleigh Plesset bubble equation based Zwart cavitation model added to the two-phase flow VOF (Volume of Fluid) method with the SST k-Omega turbulence model. In this study, the interaction of the rudder and the propeller was studied under the influence of cavitation. In this way, it is aimed to contribute to silence by reducing the cavitation caused by propeller – rudder interaction. In the study, it is aimed to minimize the cavitation caused by the Propeller-Rudder interaction in Naval Ships. For this purpose, CFD was validated by 6 different experiments in the literature. Calculations of the interaction of the low-cavitation propeller and the twisted rudder were performed using the obtained solution method. A 5-step improvement process was applied to the propeller geometry designed within the scope of the thesis. In terms of Blade Area Ratio (BAR), Pitch and Skewness of the propeller were improved. It was observed that cavitation decreased in the propeller blades as a result of reducing the pitch and increasing the skewness. The reduction of the propeller torque moment more than the thrust force helped to increase the propeller efficiency. With the improvement of the propeller made in the thesis, the cavitation rate in the existing propeller geometry was reduced compared to the original propeller geometry, and the efficiency was increased. The rudder geometry, which was passed through 4 different improvement stages, was positioned at downstream line of the resulting effective wake field of improved propeller Alternative rudders were positioned at downstream line of the improved propeller's effective wake field. When the literature is examined, the problem of course keeping is observed when using rudder geometries with increased maneuverability on ships. Due to the irregular flow from downstream line of the propeller, the rudder geometry generates lift force even in a straight position. This force creates cavitation on the rudder geometry. Cavitation was eliminated by twisting the rudder blade from middle of span. The lower chord of the rudder was twisted in the opposite direction in order to reduce the loss of maneuvering caused by twisting the rudder and the cavitation formed on its outer surface in the direction of twisting from the middle. It was seen that the double-twisted rudder at downstream line of the effective wake field of the propeller showed better performance in terms of maneuverability and cavity area than the non-twisted and single-twisted rudder.