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A system for reducing compressor noise includes a rotor having a plurality of blades. The blades have a nominal geometry characterized by a blade parameter. At least some of the blades are mistuned, such that they differ from the nominal geometry by greater than a manufacturing tolerance in the blad

A system for reducing compressor noise includes a rotor having a plurality of blades. The blades have a nominal geometry characterized by a blade parameter. At least some of the blades are mistuned, such that they differ from the nominal geometry by greater than a manufacturing tolerance in the blade parameter. The blades produce shock waves at a blade passing frequency, and the mistuned blades shift acoustic energy away from the blade passing frequency to multiple lower amplitude tones at other frequencies. The system is configurable to be deployed with an inlet silencer that preferentially absorbs acoustic energy at some of the shifted frequencies.

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1. A system for reducing compressor noise, the system comprising: a compressor for generating compressed air, the compressor comprising a plurality of blades, wherein at least some of the blades are mistuned with respect to a nominal geometry; andan inlet silencer disposed in an upstream flow direct

1. A system for reducing compressor noise, the system comprising: a compressor for generating compressed air, the compressor comprising a plurality of blades, wherein at least some of the blades are mistuned with respect to a nominal geometry; andan inlet silencer disposed in an upstream flow direction from the compressor, for absorbing acoustic energy;wherein the mistuned blades differ from the nominal geometry by at least two degrees (2°) in a sweep angle. 2. The system of claim 1, wherein the mistuned blades reduce noise intensity by shifting acoustic energy to a frequency that is preferentially absorbed by the inlet silencer. 3. The system of claim 1, wherein the noise intensity is reduced by a substantial amount with respect to a compressor in which the blades are not mistuned. 4. The system of claim 3, wherein the noise intensity is reduced by a factor of two or more. 5. The system of claim 3, wherein the noise intensity is reduced by three decibels (3 dB) or more. 6. The system of claim 1, wherein the mistuned blades differ from the nominal geometry by at least two degrees (2°) in a lean angle. 7. The system of claim 1, wherein the mistuned blades differ from the nominal geometry by at least two percent (2%) in a pitch. 8. The system of claim 1, wherein the mistuned blades differ from the nominal geometry by at least five percent (5%) in a cutback. 9. A gas turbine engine comprising: a turbine for generating rotational energy from combustion gas;a combustor for generating the combustion gas from fuel and compressed air;a compressor for generating the compressed air from the rotational energy, the compressor comprising: a plurality of blades, wherein at least some of the blades are mistuned by greater than a manufacturing tolerance in a blade parameter; anda rotor for rotating the blades at a blade passing frequency;wherein the blade parameter is one of a pitch or a cutback, and differs from a nominal geometry by five percent (5%) or more. 10. The gas turbine engine of claim 9, wherein the rotor is a centrifugal compressor rotor. 11. The gas turbine engine of claim 9, wherein the gas turbine engine is an auxiliary power unit. 12. The auxiliary power unit of claim 11, wherein the mistuned blades shift acoustic energy from the blade passing frequency to a frequency that is preferentially absorbed by an inlet silencer. 13. The auxiliary power unit of claim 11, wherein a total noise intensity of the auxiliary power unit is reduced by three decibels (3 dB) or more. 14. A compressor rotor comprising: a plurality of blades having a nominal geometry characterized by a blade parameter, and producing shock waves at a blade passing frequency;wherein at least some of the blades differ from the nominal geometry by more than a manufacturing tolerance in the blade parameter;wherein the blade parameter is one of a pitch or a cutback, and differs from the nominal geometry by five percent (5%) or more. 15. The compressor rotor of claim 14, wherein the blades that differ from the nominal geometry shift acoustic energy away from the blade passing frequency, reducing noise intensity at the blade passing frequency by at least three decibels (3 dB). 16. The compressor rotor of claim 14, wherein the blade parameter is one of a sweep angle or a lean angle, and differs from the nominal geometry by two degrees (2°) or more. 17. The compressor rotor of claim 14, wherein the compressor rotor is a centrifugal compressor rotor. 18. The compressor rotor of claim 17, further comprising splitters disposed between the blades. 19. A system for reducing compressor noise, the system comprising: a compressor for generating compressed air, the compressor comprising a plurality of blades, wherein at least some of the blades are mistuned with respect to a nominal geometry; andan inlet silencer disposed in an upstream flow direction from the compressor, for absorbing acoustic energy;wherein the mistuned blades differ from the nominal geometry by at least two degrees (2°) in a lean angle. 20. A system for reducing compressor noise, the system comprising: a compressor for generating compressed air, the compressor comprising a plurality of blades, wherein at least some of the blades are mistuned with respect to a nominal geometry; andan inlet silencer disposed in an upstream flow direction from the compressor, for absorbing acoustic energy;wherein the mistuned blades differ from the nominal geometry by at least five percent (5%) in a cutback. 21. A gas turbine engine comprising: a turbine for generating rotational energy from combustion gas;a combustor for generating the combustion gas from fuel and compressed air;a compressor for generating the compressed air from the rotational energy, the compressor comprising: a plurality of blades, wherein at least some of the blades are mistuned by greater than a manufacturing tolerance in a blade parameter; anda rotor for rotating the blades at a blade passing frequency;wherein the blade parameter is one of a sweep angle or a lean angle, and differs from a nominal geometry by two degrees (2°) or more.