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AssigneeUnited Technologies Corporation
InventorsRobert J. Manzi, Jr., Douglas C. Mathews, Soter P. Slomski, Johan van Achterberg
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The blades (38) of a gas turbine engine fan rotor (32) are uniquely distributed in the rotor hub (48) so that combination tone noise attributable to one or more physical nonuniformities in the blades is mitigated. The invention recognizes that the frequency spectrum of the combination tone noise includes both decay prone harmonics and decay resistant harmonics and that allocation of acoustic energy into the decay prone harmonics and out of the decay resistant harmonics is effective for mitigating combination tone noise. In particular, the blades are distributed so that the spatial or circumferential spectrum of the physical nonuniformity is dominated by circumferential harmonics whose order is no greater than the order of the highest decay prone harmonic of the combination tone noise spectrum.
A bladed rotor for a turbine engine, the rotor including a hub rotatable about a longitudinally extending axis and a population of blades circumferentially distributed in the hub at discrete angular locations and extending from the hub, the blades having at least one circumferentially varying physical nonuniformity which contributes to combination tone noise, the combination tone noise having a noise frequency spectrum one of whose harmonics is a cutoff harmonic of order n, n being a positive integer, the variation of each physical nonuniformity with respect to angular location having a circumferential nonuniformity spectrum, the rotor characterized in that the blades are distributed in the hub so that each circumferential nonuniformity spectrum is dominated by circumferential harmonics of order no greater than m, m being an integer specific to each nonuniformity and no greater than n so that the combination tone noise is mitigated.
A method of minimizing combination tone noise generated by a bladed rotor having a hub, which is rotatable about a longitudinally extending central axis, and a population of blades circumferentially distributed in the hub at discrete angular locations and extending from the hub, the blades having at least one circumferentially varying physical nonuniformity which contributes to combination tone noise, the combination tone noise having a noise frequency spectrum one of whose harmonics is a cutoff harmonic of order n, n being a positive integer, the method characterized by:
A method of minimizing combination tone noise generated by a bladed rotor having a hub, which is rotatable about a longitudinally extending central axis, and a population of blades circumferentially distributed in the hub at discrete angular locations and extending from the hub, the blades having at least one circumferentially varying physical nonuniformity which contributes to combination tone noise, the combination tone noise having a noise frequency spectrum one of whose harmonics is a cutoff harmonic of order n, n being a positive integer, the method characterized by:
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