Experimental Analysis of Noise Intermittency Induced by Tandem Rotor Aeroacoustic Interference

This study investigates the aeroacoustic effects of phase synchronization between co-rotating propellers in side-by-side configurations. Time-domain Proper Orthogonal Decomposition (POD) is employed on pressure fluctuation data to separate tonal and broadband components, enabling a detailed analysis of acoustic interference mechanisms. Experimental results demonstrate that synchronization significantly influences the tonal component, highlighting distinct regimes of constructive and destructive interference depending on the rotor phase delay. Specifically, the analysis reveals a notable reduction in noise amplitude at specific phase shifts, particularly affecting the second harmonic. An explanation of this scientific outcome is provided and illustrated schematically. Additionally, probability density functions indicate pronounced modifications in the statistical characteristics of pressure fluctuations related to phase synchronization, further supporting the effectiveness of the decomposition approach. he results demonstrate the effectiveness of rotor synchronization as a useful active noise control strategy in order to achieve a significant noise mitigation. A non-linear analysis is applied to the tonal component, revealing a path to chaos via intermittency during the transition between constructive and destructive interference. More in detail, a local birth and death of periodic oscillations via Hopf-like bifurcation is observed. This aspect highlights the intricate and fascinating chaotic nature of the interference transition. The chaotic behavior of the tonal component is related to the macro time scale of the pressure fluctuation, and has been incorporated into the mathematical model.