Acoustic spectra of rotor noise yield frequency distributions of energy within pressure time series. However, they are unable to reveal phase relations between different frequency components while these play a role in the fundamental understanding of low-frequency intensity modulation of higher-frequency rotor noise. A methodology to quantify interfrequency modulation is applied to a comprehensive acoustic dataset of a fixed-pitch benchmark rotor, operating at a low Reynolds number and at advance ratios ranging from J = 0 to 0.61. Our findings strengthen earlier observations in case of a hovering rotor, in which the modulation of the high-frequency noise is strongest around an elevation angle of θ = 20 ° (below the rotor plane). For the nonzero advance ratios, modulation becomes dominant in the sector 45 ° θ 0 ° and is most pronounced at the highest advance ratio tested ( J = 0.61 ). Intensity modulation of high-frequency noise is primarily the consequence of a far-field observer experiencing a cyclic sweep through the noise directivity pattern of relatively directive trailing-edge noise. This noise component becomes more intense with increasing J and is associated with broadband features of the partially separated flow over the rotor blades.


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    Title :

    Low-Frequency Intensity Modulation of High-Frequency Rotor Noise


    Contributors:

    Published in:

    AIAA Journal ; 62 , 9 ; 3374-3390


    Publication date :

    2024-09-01




    Type of media :

    Conference paper , Article (Journal)


    Type of material :

    Electronic Resource


    Language :

    English




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