Abstract
Marine propulsors are identified as the main contributor to a vessel’s underwater radiated noise as a result of tonal propeller noise and broadband emissions caused by its induced cavitation. To reduce a vessel’s signature, spectral limits are set for the propulsion industry, which can be experimentally obtained for a complete vessel at the full-scale; however, the prediction capability of the sound sources is still rudimentary at best. To adhere to the regulatory demands, more accurate numerical methods for combined turbulence and two-phase modeling for a high-quality prediction of acoustic sources of a propeller are required. Several studies have suggested implicit LES as a capable tool for propeller cavitation simulation. In the presented study, the main objective was the evaluation of the tip and hub vortex cavitating flows with implicit LES focusing on probable sound source representation. Cavitation structures for free-running propeller test cases were compared with experimental measurements. To resolve the structure of the tip vortex accurately, a priory mesh refinement was employed during the simulation in regions of high vorticity. Good visual agreement with the experiments and a fundamental investigation of the tip cavity structure confirmed the capability of the implicit LES for resolving detailed turbulent flow and cavitation structures for free-running propellers.
Highlights
The marine propeller has been identified as a primary source of underwater radiated noise [1,2], with tonal peaks at distinct blade passing frequencies, and its induced cavitation, generating broadband noise emissions
When designing a high-performance marine propeller for high-area loads and low cavitation numbers, there is always a tradeoff between efficiency and risk of cavitation, which is known to have detrimental effects that might be experienced as a loss of thrust or material erosion, and which are usually accompanied by the generation of broadband noise as a result of dynamic cavitation structures and single bubble collapses of varying diameter
The large deviations in the noncavitating part could be attributed to the missing wall model for the implicit large eddy simulation (ILES), while the further deviations in the cavitating case may be due to differences in capturing the cavitating flow behavior on the blade seen in the experiment and the simulation
Summary
The marine propeller has been identified as a primary source of underwater radiated noise [1,2], with tonal peaks at distinct blade passing frequencies, and its induced cavitation, generating broadband noise emissions. In order to reduce propeller noise emissions as part of a vessel’s underwater noise spectrum, the prediction methods are first required to reach sufficiently high accuracy over the complete frequency range of interest. State of the Art. When designing a high-performance marine propeller for high-area loads and low cavitation numbers, there is always a tradeoff between efficiency and risk of cavitation, which is known to have detrimental effects that might be experienced as a loss of thrust or material erosion, and which are usually accompanied by the generation of broadband noise as a result of dynamic cavitation structures and single bubble collapses of varying diameter. The exact topology and shape, as well as dynamic behavior, of the cavitation structures depend highly on the specific propeller design, its inflow, and operation point
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