Noise Decomposition of Dual Synchronized Propellers in Hover

This experimental study investigates the acoustic characteristics of dual propellers in the side-by-side configuration, and addresses the impact of blade tip-to-tip separation distances and relative blade-to-blade phase angles on the tonal noise generation with a specially designed propeller rig. The parametric study of co-rotating and counter-rotating configurations is performed to emphasize the effect and importance of phase synchronization in producing the tonal components, such as the first Blade Pass Frequency (BPF). The linearity of acoustic interference for the side-by-side propellers is investigated through the principle of superimposition. A unique noise decomposition algorithm for various rotation angles is developed to understand the directional behavior of the synchronized propellers. The responses of the first BPF noise radiation as a function of the rotation angle under different combinations of rotating direction and blade-to-blade phase angle have been established.