Fifth International Symposium on Marine Propulsion SMP’17, Espoo, Finland, June 2017 Numerical Prediction of Acoustic Noise Level Induced by Cavitation on Ship Propeller at Behind-Hull Condition Keita Fujiyama 1 , Yoshitaka Nakashima 1 1 Software Cradle Co., Ltd, Osaka, Japan ABSTRACT For the care of sea animals, the regulation of the noise on a marine navigation is going to be planned. It is known that the unsteady cavitation behavior on the propeller is a source of the noise, and the control of this behavior needs on the designing process. In this article, we performed the unsteady cavitating flow analyses and investigated the cavitation caused noise by using computational fluid dynamics. We also checked up the prediction methods for the cavitation caused noise by the comparing with the experimental results. Finally, we evaluated the potential of computational fluid dynamics calculations for the designing tools of the ship development. Keywords Cavitation, Pressure fluctuation, Noise prediction 1 INTRODUCTION The interaction between a wake of a ship and a rotation of its propeller causes unsteady cavitation. The cavitation causes a pressure fluctuation on a ship, which affects both the comfort on board and the fatigue strength of the ship structure. In addition, there is a possibility that the noise caused by the cavitation attacks the sea animals. To protect the sea animals, these noise must be controlled and the regulations will be planned. For these reasons, predictions of the unsteady cavitation phenomena, the pressure fluctuation by cavitation and the acoustic noise around a ship at the design phase should be essentials for the developing of ships. The studies of the propeller cavitation in a wake of a ship and the pressure fluctuation on a ship hull, using the numerical simulations, have been presented by Kanemaru et al. (2013) and Berger et al. (2013). Kanemaru et al. used the extended panel method while Berger et al. used the finite element method around the ship hull and the boundary element method for the propeller in combination. Moreover, Hasuike et al. (2011), Kawamura et al. (2010) and Sakamoto et al. (2015) simulated unsteady propeller- cavitation using CFD based on the finite element method or the finite volume method. Especially in Sakamoto et al. (2015), they calculated not only for the pressure fluctuations but also for acoustic noise predictions by the unsteady cavitation, and their predictions were well agree with the experiments. However mostly calculations for the cavitation were the performed for the model sized ship and its experiments in the cavitation tunnel. Therefore, their results need to translate using empirical formula to full size ship phenomena. In other hands, the experiment data for the full size ship are aligning now, such that the Seiunmaru series results by JSTRA (1983) in older days and new experiments results using latest measuring instruments by AQUO/SONIC projects (2016). In this paper, we performed the calculation of the unsteady cavitation and causing noise predictions using Computational Fluid Dynamics (CFD) software for both a scale sized model and a full model. From the comparing with both the calculation data and the experimental data, we evaluated the potential and the range of applications by CFD calculations, and investigated whether CFD can be applied as a noise predicting tool on a designing and developing process of the ship hull and propellers. 2 NUMERICAL MODELS All simulations in this paper were performed by the SC/Tetra Version 13, which is the commercial navier- stokes solver based on a finite volume method. To simulate a two-phase cavitating flow, the single fluid approach is used. In addition, the mixture density is treated as a compressible flow by using barotropic relation. Evaporation and condensation are modelled using a full- cavitation model. To perform acoustic noise prediction, the method by Lyrintzis which is the application of the Ffowcs Williams- Hawkings equations was used. 2.1 Cavitaion Analysis Modeling In this paper, relative motions between vapour and liquid are neglected since the flows are assumed to be uniform. In addition, a barotropic relation is used and the governing equations of mass and momentum are formally the same as those of the single phase flows (Okuda et al., 1996). Mixture density is described as follows: =∑ (1)
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Numerical Prediction of Acoustic Noise Level Induced by ...Evaporation and condensation are modelled using a full-cavitation model. To perform acoustic noise prediction, the method
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Fifth International Symposium on Marine Propulsion SMP’17, Espoo, Finland, June 2017
Numerical Prediction of Acoustic Noise Level Induced by Cavitation on Ship Propeller at Behind-Hull Condition
Keita Fujiyama1, Yoshitaka Nakashima1
1Software Cradle Co., Ltd, Osaka, Japan
ABSTRACT
For the care of sea animals, the regulation of the noise on
a marine navigation is going to be planned. It is known that
the unsteady cavitation behavior on the propeller is a
source of the noise, and the control of this behavior needs
on the designing process.
In this article, we performed the unsteady cavitating flow
analyses and investigated the cavitation caused noise by
using computational fluid dynamics. We also checked up
the prediction methods for the cavitation caused noise by
the comparing with the experimental results. Finally, we
evaluated the potential of computational fluid dynamics
calculations for the designing tools of the ship development.