Abstract
In this study, the high-fidelity numerical methods are developed to investigate the tip vortex cavitation (TVC) inception and noise of underwater propellers, namely, Model-A and Model-B, which are designed to investigate the effects of sweep angle on cavitation inception and noise. In addition, the entire body of the DARPA Suboff submarine is included to consider the effects of the inflow distortion originating from the boundary layer flow of the submarine body on the cavitating flow of the propellers. The Eulerian approach consisting of Reynolds-averaged Navier–Stokes (RANS) solver and the vortex model is coupled with the Lagrangian approach using the bubble dynamics equations and the acoustic analogy for nuclei initially distributed in inlet flow. First, three-dimensional incompressible unsteady RANS simulations are performed to predict the hydrodynamic flow field driven by underwater propellers installed on a DARPA Suboff submarine body. The Scully vortex model and dissipation vortex model (DVM) are used to regenerate the tip vortex dissipated by artificial numerical damping and low grid resolution around the vortex core center, which is identified by using minimum λ2-criterion in the swirling flow field originating from the propeller blade tip. Then, tip vortex cavitation inception is simulated by applying the bubble dynamics equations to nuclei initially distributed in the inflow region. The volume and location of each nucleus are obtained by solving the bubble dynamics equations on the flow field obtained using the Eulerian method. Finally, the cavitation noise is predicted by modeling each bubble with a point monopole source whose strength is proportional to its volume acceleration. The validity of the present numerical methods is confirmed by comparing the predicted acoustic pressure spectrum with the measured ones.
Highlights
There has been an increase in demand for propulsion systems with higher hydrodynamic performance and lower underwater-radiated noise, as environmental issues are gaining more attention in addition to the traditional military necessity
The bubble dynamics solver is validated by using the measured data, which are obtained from expansion and collapse were carefully examined
It is found that the overall SPL predicted for the Model-B is less by 6.3 to 7.1 dB than that of Model-A, while the measured one for Model-B is less by 2.7 dB than that of Model-A. These results reveal that the current numerical method can adequately appreciate the effects of sweep angle on the cavitation inception and noise of the underwater propeller of the submarine
Summary
There has been an increase in demand for propulsion systems with higher hydrodynamic performance and lower underwater-radiated noise, as environmental issues are gaining more attention in addition to the traditional military necessity. It is well known that, when the cavitation occurs on the propeller, the tonal and broadband noise increase rapidly in the wide frequency range. Sci. 2020, 10, 8721 characteristics at the rotating frequency, and the tip vortex cavitation (TVC) is of statistically ergodic characteristics in a broadband frequency range [1]. The reliable and efficient numerical methods which can be used to predict and analyze the cavitation inception and noise are essential for developing low-noise and high-performance underwater propellers, in practice by increasing the so-called cavitation inception speed (CIS)
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