Harmonic and Broadband Separation of Noise from a Small Ducted Fan

In the study of noise from propellers and ducted fans, rigorous signal decomposition into harmonic and broadband components is essential for the development of high-fidelity predictive models. Current spectral methods and phase averaging techniques lack the temporal resolution to compensate for fluctuations in operating condition intrinsic to real world experiments. In this paper we use a Vold-Kalman filter to extract the tonal and broadband content of noise from a small ducted fan simulating the conditions of an ultrahigh-bypass turbofan engine. The fan operated at pressure ratio of 1.15 and tip Mach number of 0.61. The investigation includes time traces, narrowband spectra, one-third octave spectra, and overall sound pressure level. The energies of the tonal and broadband components are similar at low frequency, while the broadband component dominates at high frequency. In addition, there are distinct differences in the directivities of the two components. The trends are in general agreement with NASA large-scale fan tests at transonic conditions.