Use of non-uniform nozzle vane spacing to reduce acoustic signature

1. A stator for a turbomachine comprising a plurality of nozzle vanes, wherein a distance between each of the plurality of nozzle vanes varies circumferentially around the stator in a repeating pattern configured to distribute a vibration energy over a plurality of side band vibration frequencies around a nominal passing frequency in a rotor; and wherein the distance between each of the plurality of nozzle vanes consecutively alternates between a first distance and a second distance, wherein the second distance is greater than the first distance.

2. The stator of claim 1 , further comprising:

a first half;

a second half, wherein a first number of the plurality of nozzle vanes are included in the first half and a second number of the plurality of nozzle vanes are included in the second half, and the distance between each of the plurality of nozzle vanes defines a flow area; and

a first sum of the flow areas between the plurality of nozzle vanes in the first half is substantially equal to a second sum of the flow areas between the plurality of nozzle vanes in the second half.

3. The stator of claim 1 , further comprising:

an inner endwall having a plurality of inner slots defined therein; and

an outer endwall having a plurality of outer slots defined therein,

wherein each of the plurality of nozzle vanes is disposed in one of the plurality of inner slots and in one of the plurality of outer slots.

4. The stator of claim 1 , wherein the distance between each of the plurality of nozzle vanes defines a nozzle having a profile, wherein varying the distance varies the profile of the nozzle.

5. The stator of claim 1 , wherein the plurality of side band vibration frequencies comprise a first side band vibration frequency corresponding to the first distance and a second side band vibration frequency corresponding to the second distance.

6. A turbomachine, comprising:

a rotor; and

a stator in fluid communication with the rotor, the stator having first nozzles each having a first profile and second nozzles each having a second profile that is larger than the first profile, wherein the first and second nozzles are disposed in a repeating pattern such that a vibration energy in the rotor is distributed among a plurality of side band vibration frequencies around a nominal passing frequency;

wherein the repeating pattern comprises a repeating sequence in which each one of the first nozzles is adjacent to at least one of the second nozzles, and each one of the second nozzles is adjacent to at least one of the first nozzles.

7. The turbomachine of claim 6 , wherein the stator further comprises:

an inner endwall that is ring-shaped and continuous and has inner slots defined therein;

an outer endwall that is ring-shaped and continuous and has outer slots defined therein, wherein the inner endwall and the outer endwall are concentric and the inner endwall is located radially inside the outer endwall; and

a plurality of nozzle vanes each extending radially between the inner endwall and the outer endwall and disposed in one of the inner slots and in one of the outer slots.

8. The turbomachine of claim 6 , wherein:

each of the first and second nozzles define a flow area;

the stator has a first half and a second half, wherein the first nozzles are distributed between the first and second halves, and the second nozzles are distributed between the first and second halves; and

a first sum of the flow areas of the first and second nozzles in the first half is substantially equal to a second sum of the flow areas of the first and second nozzles in the second half.

9. A turbomachine, comprising:

a rotor; and

a stator in fluid communication with the rotor, the stator having first nozzles each having a first profile and second nozzles each having a second profile that is larger than the first profile, wherein the first and second nozzles are disposed in a repeating pattern such that a vibration energy in the rotor is distributed among a plurality of side band vibration frequencies around a nominal passing frequency;

wherein the plurality of side band vibration frequencies comprise a first side band vibration frequency corresponding to the first nozzles, and a second side band vibration frequency corresponding to the second nozzles, wherein the second side band vibration frequency is lower than the first side band vibration frequency.

10. The turbomachine of claim 9 , wherein the stator further comprises:

third nozzles each having a third profile that is larger than the second profile; and

fourth nozzles each having a fourth profile that is larger than the third profile.

11. The turbomachine of claim 10 , wherein the repeating pattern comprises a repeating sequence of one of the first nozzles, one of the second nozzles, one of the third nozzles, and one of the fourth nozzles.

12. A method of reducing an acoustic signature, comprising:

providing a stator having nozzle vanes;

spacing the nozzle vanes apart non-uniformly to define non-uniform nozzles therebetween, wherein the non-uniform nozzles are arranged in a repeating pattern;

creating wakes in a working fluid using the nozzle vanes, wherein each of the wakes corresponds to a separate one of the nozzle vanes;

intersecting the wakes with blades on a rotor as the rotor turns;

transferring energy from the working fluid to a vibration energy in the rotor; and

distributing the vibration energy among a plurality of side band vibration frequencies around a nominal passing frequency,

wherein the non-uniform nozzles comprise a first nozzle having a first profile, a second nozzle having a second profile that is larger than the first profile, a third nozzle having a third profile that is larger than the second profile, and a fourth nozzle having a fourth profile that is larger than the third profile.

13. The method of claim 12 , wherein the plurality of side band vibration frequencies comprise a first side band vibration frequency corresponding to the first nozzle, a second side band vibration frequency corresponding to the second nozzle, a third side band vibration frequency corresponding to the third nozzle, and a fourth side band vibration frequency corresponding to the fourth nozzle.

14. The method of claim 13 , further comprising balancing the stator about a diametral line such that a first sum of flow areas in a first half of the stator is substantially equal to a second sum of flow areas in a second half of the stator.

15. A method of reducing an acoustic signature, comprising:

providing a stator having nozzle vanes;

spacing the nozzle vanes apart non-uniformly to define non-uniform nozzles therebetween, wherein the non-uniform nozzles are arranged in a repeating pattern;

creating wakes in a working fluid using the nozzle vanes, wherein each of the wakes corresponds to a separate one of the nozzle vanes;

intersecting the wakes with blades on a rotor as the rotor turns;

transferring enemy from the working fluid to a vibration energy in the rotor; and

distributing the vibration energy among a plurality of side band vibration frequencies around a nominal passing frequency,

wherein the non-uniform nozzles further comprise:

a plurality of first nozzles each having a first profile;

a plurality of second nozzles each having a second profile that is larger than the first profile;

a plurality of third nozzles each having a third profile that is larger than the second profile; and

a plurality of fourth nozzles each having a fourth profile that is larger than the third profile,

wherein the pattern comprises a repeating sequence of at least one of the plurality of first nozzles, at least one of the plurality of second nozzles, at least one of the plurality of third nozzles, and at least one of the plurality of fourth nozzles.