ÖğeFlow visualization and analytical study on the exhaust gas diffusion of a frigate(University of Rijeka, Faculty of Maritime Studies Rijeka, 2021) Dobrucalı, ErinçWind tunnel flow visualization tests were conducted to analyse the efflux velocity impacts and the yaw angle on the smoke dispersion of the exhaust for a generic frigate. An analytical study was also implemented to obtain the exhaust plume trajectories. The 1/100 scale generic frigate, having a platform for helicopters on the aft of the ship, was built and employed during the experimental study. The forward and astern cruises of the frigate were considered. It is found that the plume height and the exhaust gases momentum increase with the velocity ratio. The problem of smoke nuisance was observed for the ratios with low velocity such as K=0.2. The plume was also directed towards the helicopter platform when the yaw angles are higher than 10°. The experimental results are compared with the analytical solutions for three different velocity ratios. The compliance between the experimental and analytical results is found to be consistent. ÖğeSuppression of Tip Vortex Cavitation Noise of Propellers using PressurePores(TM) Technology(Mdpi, 2020) Aktas, Batuhan; Yılmaz, Naz; Atlar, Mehmet; Sasaki, Noriyuki; Fitzsimmons, Patrick; Taylor, DavidThis study aims to demonstrate the merits of pressure-relieving holes at the tip region of propellers, which is introduced as "PressurePores(TM)" technology as a retrofit on marine propellers to mitigate tip vortex cavitation noise for a quieter propeller. Shipping noise originates from various sources on board a vessel, amongst which the propeller cavitation is considered to dominate the overall radiated noise spectrum above the inception threshold. Thus, by strategically introducing pressure-relieving holes to modify the presence of cavitation, a reduction in the overall cavitation volume can be achieved. This mitigation technique could consequently result in a reduction of the radiated noise levels while maintaining the design efficiency as much as possible or with the least compromise. The strategic implementation of the holes was mainly aimed to reduce the tip vortex cavitation as this is one of the major contributors to the underwater noise emissions of a ship. In this paper, the details and results of a complementary numerical and experimental investigation is presented to further develop this mitigation concept for underwater radiated noise (URN) and to validate its effectiveness at model scale using a research vessel propeller. An overall finding from this study indicated that a significant reduction in cavitation noise could be achieved (up to 17 dB) at design speed with a favourable strategic arrangement of the pressure pores. Such a reduction was particularly evident in the frequency regions of utmost importance for marine fauna while the propeller lost only 2% of its efficiency. ÖğeExperimental and numerical investigations of tip vortex cavitation for the propeller of a research vessel, "The Princess Royal"(Pergamon-Elsevier Science Ltd, 2020) Yılmaz, Naz; Dong, Xiaoqian; Aktas, Batuhan; Yang, Chenjun; Atlar, Mehmet; Fitzsimmons, Patrick A.The present study includes experimental and numerical investigations on propeller cavitation phenomena, particularly the tip vortex cavitation, for the test cases conducted with the model propeller of the Newcastle University research vessel, "The Princess Royal". These test cases were recommended recently as the benchmark data for cavitation observations and noise measurements by the ITTC, and have been tested in a major round-robin campaign by eight cavitation tunnel/basin facilities around the world. This round-robin test campaign included the Newcastle Emerson Cavitation Tunnel where the first set of tests was conducted. This study presents further systematic measurements conducted in the Shanghai Jiao Tong University (SJTU) cavitation tunnel with this benchmark propeller in the open water conditions, including the cavitation observations, and tests for the tip vortex cavitation inception and desinence. Also, the study includes computational fluid dynamics (CFD) investigation to discuss the results of the experiments, especially the tip vortex cavitation, in a comparative manner. To simulate tip vortex cavitation, the newly developed adaptive mesh approach MARCS (Mesh Adaption Refinement Approach for Cavitation Simulations) was further enhanced. The results of the CFD computations using this approach showed good agreement with the results of the tunnel tests for the open water propeller performance characteristics, cavitation observations and tip vortex cavitation pattern, including its extent. ÖğeAn experimental and numerical investigation of propeller-rudder-hull interaction in the presence of tip vortex cavitation (TVC)(Pergamon-Elsevier Science Ltd, 2020) Yılmaz, Naz; Aktas, Batuhan; Atlar, Mehmet; Fitzsimmons, Patrick A.; Felli, MarioThis paper presents the investigation of propeller-rudder-hull interaction by using Computational Fluid Dynamics (CFD), and Experimental Fluid Dynamics (EFD) approaches including the propeller's performance in cavitating conditions, particularly the effect of the tip vortex cavitation on the interaction phenomenon. The investigation was focused on the recently generated benchmark test data for the research catamaran, The Princess Royal, and its scaled model which was tested for cavitation and noise investigations in the large circulating water channel of CNR-INM, Italy within the scope of the European collaborative project. The propeller-rudder-hull interaction of a 1/3.4 scaled model of this vessel was simulated by using the commercial CFD software, STAR-CCM+, which implemented the Schnerr-Sauer cavitation model for the cavitation effect. Large Eddy Simulations (LES) was used for a better resolution of high velocity and pressure gradients to model the tip vortex cavitation. A new adaptive meshing technique using a Mesh Adoption Refinement Approach for Cavitation Simulations (MARCS) was applied for more effective modelling of the tip vortex cavitation during the propeller-rudder-hull interaction. The results of the CFD simulations were compared with the EFD data, particularly for the cavitation dynamics.