Influence of the load conditions on the acoustic signature of a tip-loaded propeller with winglets

The Ffowcs-Williams and Hawkings acoustic analogy was exploited to reconstruct the acoustic signature of a tip-loaded propeller with winglets across a range of working conditions, from design toward higher loads. Results of Large-Eddy Simulations, conducted on a computational grid consisting of about 5 x 10(9) points, were utilized. For decreasing values of the advance coefficient, that is for increasing rotational speeds of the propeller, the rise of the values of acoustic pressure was found faster than linear, approximating a logarithmic growth. This result was verified in line with the behavior by the turbulent fluctuations on the surface of the propeller and in its wake system, which were the major sources of the loading and quadrupole components of sound, respectively. The former was the leading one on the propeller plane and at radial coordinates away from the wake system, while the latter was higher at smaller radial coordinates in the vicinity of the wake system. In addition, increasing loads on the propeller blades resulted in an outward shift of the boundary of the computational domain where the lead of the acoustic signature switched from the non-linear sources within the wake to the linear ones on the propeller surface.