This research was an experimental investigation of the aeroacoustic response characteristics of a ten-bladed rotor to grid-generated turbulence. In order to empirically characterize the rotor response, both the ingested velocity field and resulting far-field sound were measured. The detailed velocity characterization included: a high-resolution mapping of the spatial distribution of the mean velocity and RMS turbulence fluctuation in the rotor plane; discrete, empirical estimates of the 2D streamwise/radial and streamwise/tangential wave number spectral densities of the turbulence; and an evaluation of the streamwise development of “nearly isotropic” conditions at the rotor inlet plane. In addition to the discrete, 2D spectral densities, a semi-empirical, functional representation of the full, 3D wave number spectral density of the ingested turbulence was developed. This turbulence model was used, in conjunction with theoretical spectral analysis techniques, to predict the sound pressure levels in the far-field. These predictions were compared to corresponding measured data, to assess the fidelity of the spectral analysis methods and the semi-empirical turbulence model. The measured ten-bladed acoustic response was also compared to the corresponding response of a four-bladed rotor ingesting the same grid-generated turbulence field, to demonstrate the effect of blade spacing on rotor turbulence ingestion noise.
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