Time and Frequency Domain Analysis of Acoustic Pressure From Rotating Forces

This paper presents a unified analytical framework for investigating the acoustic pressure generated by rotating point forces, with a specific focus on comparing time and frequency domain formulations. Both approaches show consistent results, yet each offers distinct advantages: the time domain provides intuitive insight into the unsteady and steady loading contributions, while the frequency domain facilitates modal decomposition and easier calculation of periodic pressure. We model multiple evenly spaced blades as point forces with axial, drag and radial components. The force magnitude varies with time as a Gaussian pulse representing scenarios such as installed rotors encountering periodic loading or isolated gusts. Periodic and aperiodic cases are examined in both the time and frequency domain, revealing the conditions for constructive and destructive inter-blade interference. This study also highlights the limitations and benefits of each formulation. Time domain methods are more intuitive for the aperiodic case but require careful calculation of the retarded times. Frequency domain methods are more efficient for periodic analysis and compatible with modal acoustic models but can obscure the effects of inter-blade interaction. Collectively, these insights enhance our understanding of the mechanisms and spatial characteristics of rotor noise in installed configurations.