Prediction of noise and acoustical spectrum of counter-rotating propellers

The acoustical performance of a counter-rotating marine propeller system is computed using the Ffowcs, Williams and Hawkings (FWH) algorithm. The solution procedures, where finite volume computational fluid dynamics calculations were exploited, was validated with a conventional propeller having experimental results (namely David Taylor Model Basin [DTMB] 4119). The large eddy simulation formulation and the sliding mesh technique are employed to build thrust and torque curves. Mesh dependency, turbulence model, and discretization schemes were all assessed to have repeatable and accurate results. Because the application under consideration involved inhomogeneous flow and blade interactions, DTMB 3684 and 3685 counterrotating propeller (CRP) models were used for comparisons. In terms of validation of numerical acoustics, the acoustical model evaluation study was first performed on a flow over a cylinder and a rain gutter model. The FWH approach produced good results for the spectrum at near-field and far-field locations. The performance of an inclined propeller, namely VP1304, in a noncavitating condition was investigated and the results were compared with the experiments conducted at the Potsdam Model Basin. Pressure pulses of this propeller in the cavitation tunnel were also attained and compared with experimental results. The amplitudes of the pressure fluctuations were in good agreement with the experimental data except for the weak third harmonics. Last, the generic form of the CRP systemattached to an underwater vehicle body was considered to investigate the acoustic spectrum in terms of blade passing frequencies, interacted harmonics and radiated noise.