Investigation of Propeller Noise Using LES and an Acoustic Analogy

The flow field of a five-bladed marine propeller operating at design condition is used to calculate far-field sound. The flow field is obtained using large eddy simulation (LES) and far-field sound is computed using the Ffowcs-Williams and Hawkings acoustic analogy. The physics of sound generation is examined by analyzing both the near-propeller flow field and far-field sound. While the blades generate strongly tonal noise, the overall acoustic signature of the propeller is broadband. The propeller is found to be acoustically compact at frequencies up to 100 times the rotation rate. The majority of sound is generated by localized unsteadiness at the blade tip, due to shedding of the tip vortex. Two other notable sound generation mechanisms are: convection of boundary layer turbulence past the blade trailing edge and interaction of the blade root wakes with the propeller-hub surface. Acoustic energy is found to be distributed among higher frequencies as local Reynolds number increases radially along the blades.