Abstract
The study numerically investigated and compared noise dissipation, cavitation, output power and energy produced by marine propellers. A Ffowcs Williams-Hawkings (FW-H) model was used to determine speed ratio, sound pressure levels, vortex shedding, and the distance of noise sources, receivers, and a fixed advancing ratio. The FW-H model was applied to predict different blade geometries’ output noise and vortex shedding over varied Reynolds and Strouhal numbers.
The large eddy simulation model best predicted the turbulent structures’ spatial and temporal variation, which would better illustrate the flow physics. It was found that a high angle of incidence between a blade’s leading edge and the water flow direction typically causes the hub vortex to cavitate. The roll-up of the cavitating tip vortex was closely related to propeller noise. The effects of sound pressure level at two observation positions of a fixed and varied blade pitch angle at the low Mach unsteady incompressible Reynolds-averaged Navier-Stokes flow approach was studied.
The study investigated three and five blade configurations of marine propellers since they are commonly used for boats. The five-blade propeller was quieter under the same dynamic conditions such as the advancing ratio, compared to three- or four-blade propellers. The importance of shipping noise and its impact on the marine environment is demonstrated by the fact that at low frequencies, below 300 Hz, ambient noise levels have increased by 15-20 dB over the last century. The noise in the low-frequency range of 10 Hz to 1 kHz immensely affects the marine biological system. It was found that stream division and vortex shedding are unstable occasions that force wavering tension on the propeller. Cavity development responds to the significant large pressure fluctuation around the blade. Acoustic characteristics, such as propeller noise, consist of loading and cavitation noises. They increased the maximum sound pressure level for the cavitation noise on the low Mach five blades by 23.2%.
Keywords: Cavitation, computational fluid dynamics, noise acoustics, vortices, shedding, sound pressure level