Acoustic behavior of a rotating body through the Ffowcs Williams-Hawkings equation

This paper deals with the use of the Ffowcs Williams-Hawkings equation for acoustic analysis of propellers and the deep difference between the aeroacoustic and hydroacoustic fields generated by similar propulsion devices in air and underwater. This dissimilarity does not depend either on the different fluid, or the (although existing) geometric and structural difference of the blades: it is an intrinsic feature of the generating noise mechanisms related to rotating sources and is due to the remarkable diversity of the rotational speed. The analysis points out the general behavior of the surface integral kernels of the standard solving formula, by referring to an elemental, rotating point source and by showing its relationship with a general multi-bladed device.