Numerical Analysis On Cavitation And Noise Performance Of Duct Propeller

Cavitation inevitably occurs on duct propellers due to the increasing load on the blades as the increasing demand of power and speed for new-building ships.As a result,the problems of the detoriation of hydrodynamic performance and the cavitation induced erosion,vibration and noise will impact the ship propulsion performance and the safety and reliability of the whole system,which threatening the ship stealthiness.This paper numerically analyzes the hydrodynamic performance,cavitation and noise performance of the duct propeller based on the RANS method.It has important significance for the improvement of the overall properties of the duct propeller,which can also provide certain numerical and theoretical support for the study of the cavitation induced noise,vibration and erosion.Firstly,the software STAR-CCM+ has been applied to perform the numerical simulation of the open-water performance of the duct propeller by using the Reynolds-averaged Navier-Stokes(RANS)method together with two-equation turbulence models based on the pressure-based viscous solver.It carries out the verification of grid sensitivity and the analysis of the influence of different turbulent models on the numerical results by comparing with the open-water test results conducted by the towing tank of Wuhan University of Technology.The results show that the open-water characteristics predicted by the RANS method with the Realizable turbulence model in the current mesh topology can be applied for practical engineer application.Then the unsteady hydrodynamic performance of the duct propeller is calculated under a given experimental axial wake based on the unsteady RANS method.Then VOF two-phase model and the Schnerr-Sauer cavitation model are adopted to calculate the cavitation performance of the duct propeller.The accuracy and reliability of the numerical results are validated by comparison with the cavitation tunnel test results.The cavitation pattern,hydrodynamic performance and cavitation induced pressure fluctuations are then analyzed.It is found that the hydrodynamic performance of the duct propeller is reduced when the cavitation occurs,and the total thrust and torque vary with large magnitudes.The maximum pressure amplitude isfound at the monitor point near to the leading edge of the duct,but the first order amplitudes of pressure fluctuations on these fixed points are all within the safety range.Finally,the non-cavitation load noise,cavitation load noise and cavitation radiation noise are calculated in the current study based on fun noise source method combining with the boundary element method and the pulse spherical bubble theory.At first,the load noise of E779 A propeller is calculated by fan source method combined with CFD method and the result is compared with the reference value to verify the accuracy of the method.The comparison between the non-cavitation load noise and cavitation load noise shows that the cavitation load noise is smaller than the non-cavitation one,however,with less difference in the acoustic directivity.The cavitation monopole radiation noise is finally predicted by using he pulse spherical bubble theory.It shows that the cavitation radiation noise is larger than the load noise and will become the main noise source when cavitation occurs.