Comparison between the acoustic fields of conventional and tubercled propellers

Abstract

The results of large eddy simulations on a cylindrical grid consisting of 5.8 × 109 points are utilized to reconstruct the acoustic fields radiated by conventional and tubercled propellers in wetted conditions, using the Ffowcs Williams and Hawkings acoustic analogy. The analysis of the flow features demonstrates that while the distribution of the turbulent fluctuations of pressure on the surface of the propeller blades is substantially affected by the presence of leading edge tubercles (LETs), this is not the case for the wake flow, which does not display dramatic differences across cases. As a result, while the loading component of the acoustic field, which is the leading one at most frequencies, is significantly modified by the implementation of LETs, this is not the case for the quadrupole component, which is rather similar between conventional and tubercled geometries. The loading sound of the tubercled propellers is reduced around the blade frequency, f b , while it is reinforced at higher frequencies, around 10 f b . Furthermore, while the loading sound was found usually the leading one, at the highest resolved frequencies, above 20 f b , the quadrupole sound was verified more intense than the linear one, even in the acoustic far field, for both conventional and tubercled propellers.