GB2471152A - Use of Bowed Vanes to reduce Acoustic Signature - Google Patents

Abstract

A stage for a turbomachine including a rotor and a stator 18. The rotor is disposed about a shaft of the turbomachine, operatively engages the shaft, and is configured to rotate in a circumferential direction. The rotor also has a plurality of blades. The stator 18 is in fluid communication with the rotor and is located axially adjacent to the rotor. The stator 18 includes a plurality of nozzle vanes 24, an interior circumferential surface 26, and an exterior circumferential surface 28. The plurality of nozzle vanes 24 are spaced circumferentially apart to channel a working fluid therebetween, and are also bowed, or curved, to create bowed wakes in the working fluid. The bowed wakes are configured to engage the rotor blades incrementally such that the effects of the periodic disruption of forces on the blades are more gradual and/or reduced.

Description

USE OF BOWED NOZZLE VANES TO REDUCE ACOUSTIC SIGNATURE

Cross-Reference to Related Applications

[001] This application claims priority to U.S. Provisional Patent Application Serial No. 61/187,929, Attorney Docket No. 42495.47, filed June 17, 2009.

Background

[002] In a turbomachine, such as a turbine, a working fluid is motivated between nozzle vanes on a stator to blades of a rotor, which transfers energy from the working fluid to a shaft attached to the rotor. This energy may also create noise. The noise may be created in any of several manners, including when the rotor vibrates in reaction to forces applied by the working fluid on the blades. The working fluid is channeled toward the blades by the nozzle vanes of the stator. In channeling the working fluid, the nozzle vanes also create wakes in the working fluid. Each wake may represent an area of decreased velocity in the working fluid, and therefore the working fluid in the wakes may apply greater or reduced amounts of force on the blades. After the blade passes through the wake, the force applied by the working fluid returns to a relatively constant level until the blade reaches the next wake. This periodic change in forces may cause vibration. Nozzle vanes are typically straight, and thus may create straight wakes. However, the entirety of a straight wake may engage a passing blade simultaneously.

This may maximize the disruption in forces caused by the wake, thereby potentially maximizing the noise. Therefore, what is needed is a stator having nozzle vanes that change the characteristics of the wakes, such that the effects of the periodic disruption of forces on the blades are more gradual and/or reduced.

Summary

[003] Embodiments of the disclosure may provide a stator for a turbomachine. The exemplary stator includes an interior circumferential surface, and an exterior circumferential surface that is spaced radially apart from the interior circumferential surface. The exemplary stator also includes a plurality of nozzle vanes extending between the interior circumferential surface and the exterior circumferential surface, The plurality of nozzle vanes are spaced circumferentially apart to channel a working fluid therebetween. Each one of the plurality of nozzle vanes are bowed to create bowed wakes in the working fluid. The bowed wakes are each configured to incrementally engage blades of the turbomachine, [004] Embodiments of the disclosure may further provide a stage for a turbomachine, with the exemplary stage including a rotor and a stator. The rotor is disposed about a shaft of the turbomachine, operatively engages the shaft, and is configured to rotate in a circumferenUal direction. The rotor also has a plurality of blades. The stator is in fluid communication with the rotor and is located axially adjacent to the rotor. The stator includes a plurality of nozzle vanes. The plurality of nozzle vanes are spaced circumferentially apart to channel a working fluid therebetween. The plurality of nozzle vanes are also bowed to create bowed wakes in the working fluid. The bowed wakes are configured to engage the plurality of blades incrementally.

Brief Description of the Drawings

[005] The present disclosure is best understood from the fotlowing detailed description when read with the accompanying Figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

[006] Figure 1 illustrates a partial cross-sectional view of an exemplary embodiment of a

turbine in accordance with the disclosure.

[007] Figure 2 illustrates a partial isometricviewof an exemplaryembodimentofa statorfrom a raised axial upstream perspective in accordance with the disclosure.

[008] Figure 3 illustrates an isometric view of an exemplary embodiment of a nozzle vane from a raised axial upstream perspective in accordance with the disclosure.

[009] Figures 4A and 48 illustrate raised isometric views of an exemplary embodiment of a bowed nozzle vane creating a bowed wake that incrementally engages a blade of a rotor.

Detailed Description

[0010] It is to be understood that the following disclosure describes several exemplary embodiments for implementing different features, structures, or functions of the invention, Exemplary embodiments of components, arrangements, and configurations are described below to simplify the present disclosure, however, these exemplary embodiments are provided merely as examples and are not intended to limit the scope of the invention. AdditionaUy, the present disclosure may repeat reference numerals and/or letters in the various exemplary embodiments and across the Figures provided herein. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various exemplary embodiments and/or configurations discussed in the various Figures. Moreover, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed interposing the first and second features, such that the first and second features may not be in direct contact. Finally, the exemplary embodiments presented below may be combined in any combination of ways, i.e., any element from one exemplary embodiment may be used in any other exemplary embodiment, without departing from the scope of the disclosure.

(0011] Additionally, certain terms are used throughout the following description and claims to refer to particular components. As one skilled in the art will appreciate, various entities may refer to the same component by different names, and as such, the naming convention for the elements described herein is not intended to limit the scope of the invention, unless otherwise specifically defined herein. Further, the naming convention used herein is not intended to distinguish between components that differ in name but not function. Further, in the following discussion and in the claims, the terms "including" and "comprising" are used in an open-ended fashion, and thus should be interpreted to mean "including, but not limited to," All numerical values in this disclosure may be exact or approximate values unless otherwise specifically stated. Accordingly, various embodiments of the disclosure may deviate from the numbers, values, and ranges disclosed herein without departing from the intended scope.

[0012] Figure 1 illustrates an exemplary turbomachine, specifically, a turbine 10, which may be a steam turbine, or any other turbine or expander. The turbine 10 generally includes a fluid passageway 19, a portion of which is defined between locations 11 a and 11 b, with the location ha being upstream from the location lib. The turbine 10 may also include a shaft 12, a casing 13, seals 14, rotors 16, and stators 18. Each rotor 16 is disposed around the shaft 12, and may engage the shaft 12, or may be formed integrally with the shaft 12, such that the shaft 12 rotates along with the rotor 16. The rotors 16 include a plurality of blades 33 disposed around the rotor 16, with at least a portion of the blades 33 being disposed in the fluid passageway 19. Each stator 18 may also be disposed around the shaft 12, but may be attached to the casing 13 and configured to remain stationary with respect to the rotor 16. One of the seals 14 may be interposed between each stator 18 and the shaft 12, to prevent a' substantial leakage therebetween. Additionally, each rotor 16 may be adjacent to a separate one of the stators 18, thereby defining stages 20 and 22. in an exemplary embodiment, two of the rotors 16 and stators 18 are configured to create two impulse stages 20, and two of the rotors 16 and stators 18 are configured to create two reaction stages 22. It will be apparent that other arrangements of the stages 20, 22 may be employed, and the exemplary arrangement of the Impulse stages 20 and reaction stages 22 is not to be considered limiting.

Additionally, the stages 20, 22 may Include additional rotors 16 and/or stators 18 where appropriate.

(0013] Each stator 18 may have an interior circumferential surface 26 and an exterior circumferential surface 28, with the exterior circumferential surface 28 spaced radially apart from the interior circumferential surface 26. Each stator 18 has a plurality of nozzle vanes 24, whIch may extend radially between the Interior circumferential surface 26 and the exterior circumferential surface 28 of the stator 18. The nozzle vanes 24 are disposed at least partially in the fluid passageway 19. The nozzle vanes 24 may each have a leading edge 30 and a trailing edge 32. In an exemplary embodiment, the leading edge 3Ols disposed closer than the trailing edge 32 to the location I Ia. Further, the leading edge 30 of each nozzle vane 24 may define the upstream axial extremity of each nozzle vane 24, and the trailing edge 32 may define the downstream axial extremity of each nozzle vane 24.

[0014] FIgure 2 Illustrates a partial isometric view of a portion of a stator 18 from a raised axial upstream perspective. The stator l8is generally annular, and the nozzle vanes 24, which are disposed around the stator 18, are spaced clrcumferentially apart Additionally, as described with reference to Figure 1, the nozzle vanes 24 extend between the interior circumferential surface 26 and the exterior circumferential surface 28. FIgure 2 also illustrates the leading edges 30 definIng the Sal upstream extremity of the nozzle vanes 24, as described with reference to Figure 1.

[0015] Figure 3 illustrates an exemplary nozzle vane 24. Each lndMdual nozzle vane 24 has a hub 25a defined where the nozzle vane 24 meets the interior circumferential surface 26, and a tip 25b defined where the nozzle vane 24 meets the exterior circumferential surface 28 (shown in Figure 2). The leading edge 30 of the exemplary nozzle vane 24 Is bowed between the hub 26a and the tip 25b. As shown, the leading edge 3Ois bowed laterally. As can better be appreciated from Figure 2, the nozzle vanes 24 are disposed around the annular stator 18, and thus what appears to be a lateral bow In Figure 3, is actually a bow in the circumferential axis C. Additionally, the leading edge 30 may be bowed along the axial axis A as well, but in the exemplary embodiment shown, the bow in the leading edge 30 is substantially in the circumferential axis C. [0016] A line 40a tangent to the leading edge 30 at the hub 25a forms a first angle c with respect to a line r1, which is drawn parallel to the radial axis R. Likewise, a line 40b tangent to the leading edge 30 at the tip 25b forms a second angle a2 with respect to the line r1 Since the leading edge 30 may be bowed in directions along both the axial and the circumferential axis A, C, the first and second angles ai, a2 may have both a circumferential and an axial component, but in the illustrated exemplary embodiment, the first and second angles ai, a2 are substantially made up of the circumferential component.

[0017] The bowed leading edge 30 may be described as having a first bow angle. The first bow angle is defined as the greatest angle between the line r1 and a line drawn tangent to the leading edge 30. In an exemplary embodiment wherein the leading edge 30 is bowed from the hub 25a to the tip 25b, the first bow angle is the greater of the first angle al and the second angle cL2. If the first and second angles al, a2 are equal, the first bow angle refers to both of the first and second angles ai, a2. The first bow angle may indicate how far from the line r1 the leading edge 30 is bowed. This may also be described as the depth of the bow. Accordingly, the greater the first bow angle, the deeper the leading edge 30 may be bowed. The first bow angle may be between about 20 degrees and about 40 degrees, depending on the required depth of the circumferential bow in the leading edge 30. In other exemplary embodiments, the first bow angle may be between about 25 degrees and about 35 degrees, or between about 27 degrees and about 33 degrees, or the first bow angle may be about 30 degrees.

[0018] The first bow angle may also be distributed along the leading edge 30, that is, an angle between the line r1 and a line drawn tangent to the leading edge 30 may proceed from the first angle c, to zero at a vertex V1 defined on the leading edge 30, to the second angle a2. The distribution may vary or it may be uniform, and in an exemplary embodiment, the leading edge may have a symmetric parabolic bow; alternatively, the distribution may be any other spanwise distribution that is found to be advantageous through testing and/or analysis.

Add itionally, the first bow angle may be distnbuted to a mid-span 36, which indicates that the vertex V1 of the leading edge 30 is located at the mid-span 36. The leading edge 30 may also be symmetric about the mid-span 36, The mid-span 36 is a line drawn at the radial middle of the nozzle vane 24 between the hub 25a and the tip 25b. Additionally, the leading edge 30 may have multiple bows between the hub 25a and the tip 25b (structure not depicted).

[0019] In an exemplary embodiment, the trailing edge 32 of the nozzle vane 24 is also bowed between the hub 25a and the tip 25b. Like the leading edge 30, the bowing of the trailing edge 32 may have both a circumferential and an axial dimension. As shown, the nozzle vane 24 may be curved between the leading edge 30 and the trailing edge 32 from straight along the axial axis A. The curve may give the trailing edge 32 a different orientation than the leading edge 30. The trailing edge 32 may therefore bow to a greater extent in the axial axis A than the leading edge 30 bows; however, in an alternative exemplary embodiment, the trailing edge 32 may bow to a lesser extent in the axial axis A. Thus, while the shapes of the leading edge and the trailing edge 32 may be congruent, they may be oriented in different directions.

Accordingly, while the first and second bow angles may have the same measurement, the axial component of the first bow angle may be less than the axial component of the second bow angle.

[0020] As shown, the trailing edge 32 is bowed between the hub 25a and the tip 25b in the circumferential axis C and the axial axis A. A line 41 a drawn tangent to the trailing edge 32 at the hub 25a forms a first angle with respect to a line r2, which is drawn parallel to the radial axis R. Likewise, a line 41b drawn tangent to the trailing edge 32 at the tip 25b forms a second angle 2 with respect to the line r2. Both of the first and second angles 13i, 2 may have circumferential and axial components according to the above-described orientation of the leading edge 30.

[0021] The bowed trailing edge 32 may be described as having a second bow angle, which is defined as the greatest angle formed between the line r2 and a line drawn tangent to the trailing edge 32. In an exemplary embodiment wherein the trailing edge 32 is bowed from the hub 25a to the tip 25b, the second bow angle is the greater of the first angle 13i and the second angle t32. If the first and second angles 2 are equal, the second bow angle refers to both.

The second bow angle may indicate how far from the line r2 the trailing edge 32 is bowed between the hub 25a and the tip 25b, which may also be described as the depth of the bow, Accordingly, the greater the second bow angle, the deeper the trailing edge 32 may be bowed.

The second bow angle may be between about 20 degrees and about 40 degrees, depending on the required depth of the circumferential bow in the trailing edge 32. In other exemplary embodiments, the second bow angle may be between about 25 degrees and about 35 degrees, or between about 27 degrees and about 33 degrees, or the second bow angle may be about 30 degrees.

[0022] The second bow angle may also be distributed along the trailing edge 32, that is, an angle between the line r2 and a line drawn tangent to the trailing edge 32 may proceed from the first angle, to zero at a vertex V2 defined on the trailing edge 32, to the second angle 132 In various exemplary embodiments, the distribution may vary or it may be uniform, and in an exemplary embodiment, the trailing edge 32 may have a symmetric parabolic bow; alternatively, the distribution may be any other spanwise distribution that is found to be advantageous through testing and/or analysis. Additionally, the second bow angle may be distributed to the mid-span 36, such that the vertex V2 is located at the mid-span 36, as described in reference to the leading edge 30. The trailing edge 32 may also be symmetric about the mid-span 36. Additionally, it will be appreciated that the trailing edge 32 may have multiple bows between the hub 25a and the tip 25b (structure not shown).

[0023] Figures 2 and 3 further illustrate an exemplary embodiment of the nozzle vane 24 being bowed from hub 25a to tip 25b along the entirety of the nozzle vane 24, Le., between the leading edge 30 and the trailing edge 32. Beginning at the leading edge 30, the bow from the hub 25a to the tip 25b of the nozzle vane 24 may be substantially circumferential, according to the substantially circumferential bow in the leading edge 30. As mentioned, the nozzle vane 24 is shaped such that it curves away from straight along axial axis A, from the leading edge to the trailing edge 32. For example, a cross-section of the nozzle vane 24 taken proximal to the leading edge 30 may be substantially in an axial plane, while a cross-section taken proximal to the trailing edge 32 may be in multiple axial planes.

[0024] The nozzle vane 24 may bowed from the hub 25a to the tip 25b between the leading edge 30 and the trailing edge 32 to a uniform degree. In an exemplary embodiment, the first and the second bow angles may be equal, and thus the nozzle vane 24 may be bowed uniformly between the leading and trailing edges 30, 32. Further, the bow of the nozzle vane 24 may vary or be distributed to and/or symmetrical about the mid-span 36, and each axial cross-section of the nozzle vane 24 may have a symmetric parabolic shape. In another exemplary embodiment, each axial cross-section of the nozzle vane 24 may have any other spanwise distribution found to be advantageous through testing and/or analysis.

[0025] In other exemplary embodiments, the first bow angle of the leading edge 30 and the second bow angle of the trailing edge 32 may have different measurements and/or different distributions, and thus the nozzle vane 24 may start at the geometry of the leading edge 30 and deepen, flatten, or otherwise vary, as desired, to distribute the difference between the shapes of the leading edge 30 and the trailing edge 32. Further, in another exemplary embodiment, the bowing of the nozzle vane 24 may deepen, flatten, or otherwise vary, between the leading edge 30 and the trailing edge 32 repeatedly and/or randomly as desired.

[0026] Figures 4A and 4B illustrate embodiments of the nozzle vane 24 in one of the impulse stages 20 (shown in Figure 1). It will be appreciated, however, that embodiments of the nozzle vanes 24 may also be used in reaction stages 22 (also shown in Figure 1). As described with reference to Figures 2 and 3, the nozzle vanes 24 are bowed along the circumferential axis C; more particularly, as shown in Figures 4A and 4B, the nozzle vane 24 may be bowed in the circumferential direction c1. The direction c1 is the direction in which the blade 33 proceeds; however, in other embodiments, the blade 33 may proceed in the opposite circumferential direction. As the blade 33 is attached to the rotor 16 (see Figure 1), the direction in which the blade 33 proceeds is also the direction in which the rotor 16 rotates, and thus the nozzle vane 24 may be bowed in the same direction in which the rotor 16 rotates, as shown. Additionally, as described with reference to Figure 3, the nozzle vane 24 may be curved from leading edge to trailing edge 32. The curve may allow the nozzle vane 24 to channel a working fluid 34 toward the blade 33.

[0027] When the fluid flow field of the working fluid 34 is substantially constant, i.e., between the nozzle vanes 24, the forces applied on the blades 33 are also relatively constant.

However, each of the nozzle vanes 24 disrupts the flow of the working fluid 34, thereby each creating a wake 44. A given one of the blades 33 will traverse the wake 44 each time the blade 33 passes circumferentially by the nozzle vane 24. Since the wake 44 may not have the same characteristics as the rest of the fluid flow field, the working fluid 34 in the wake 44 may apply a different force on the blade 33 than the working fluid 34 outside of the wake 44 applies.

Accordingly, when the wake 44 engages the blade 33, it may thereby produce a disruption in what might otherwise be a relatively stable force-to-time relationship in the blade 33. Since the rotor 16, upon which the blade 33 is located, as shown in Figure 1, rotates at a relatively constant speed overall, the blade 33 may encounter the wakes 44 created by the nozzle vanes 24 at a relatively constant rate. Thus, the wake 44 may engage the blades 33 at a defined period, leading to cyclic disruptions in the force applied on the blades 33.

[0028] When the wake 44 engages the blade 33, the rate at which the blade 33 is motivated may change, according to the change in force applied, and may increase or decrease, potentially repeatedly, at a rapid rate for the short period of time that the blade 33 is in the wake 44. This may cause the blade 33 to shake or vibrate, thereby creating, or at least adding to, an acoustic signature. While the numbers of nozzle vanes 24 and blades 33 forming each of the stages 20 or 22 may be selected such that not all wakes 44 engage the blades 33 at the same instant, several of the wakes 44 may come close to engaging more than one of the blades 33 at any given time, which may compound the effects of the disruption caused by each wake 44.

[0029] The exemplary nozzle vane 24 shown in Figures 4A and 4B is bowed from hub 25a to tip 25b, as described with reference to Figures 2 and 3, such that the wake 44 it produces is correspondingly bowed and may incrementally engage the blade 33. As shown in Figure 4A, the outer extremities of the wake 44 may engage the blade 33 first. As the blade 33 proceeds circumferentially in the direction c1, incrementally more of the wake 44 engages the blade 33, as shown in Figure 4B, until all of the wake 44 may engage the blade 33. Subsequently, the blade 33 may begin to pass out of the wake 44. In this way, the wake 44 incrementally engages the blade 33, thereby reducing the rate at which the disruption in the forces in the working fluid 34 is realized by each blade 33, and reducing the magnitude of the vibrations.

Thus, the force-to-time relationship during the disruption becomes more stable: the force may change by the same amount, but the wake 44 engages the blade 33 incrementally, over a longer period of time, as opposed to instantaneously engaging the blade 33 in straight-vane designs (not shown). It will be appreciated that the incremental engagement of the wakes 44 by the blades 33 may also be described as a gradual engagement, as opposed to the aforementioned instantaneous engagement, in which the portion of the wake 44 engaged by the blades 33 slowly (relative to the near instant time period of straight-vane designs) increases overtime. As the forces become more stable, the amplitude of the vibration may be reduced, thereby reducing the acoustic signature of the turbine I 0.

[0030] The foregoing has described an exemplary stator for a turbomachine comprising an interior circumferential surface; an exterior circumferential surface spaced radially apart from the interior circumferential surface; and a plurality of nozzle vanes extending between the J....L.:.r. ..: ..a... ...ru.........: .....n.. . .. . ..:. ... :.... ....n: interior circumferential surface and the exterior circumferential surface, spaced clrcumferentlally apart to channel a working fluid therebetween, and bowed to create bowed wakes in the working fluid, wherein the bowed wakes are configured to incrementally engage blades of the turbomachine. Further, the stator as above, wherein the plurality of nozzle vanes are bowed In an axial direction and In a circumferential direction, and/or wherein the plurality of nozzle vanes are bowed in a spanwise distribution. Additionally, the stator as above wherein the plurality of nozzle vanes are bowed symmetrically to a mid-span, and/or wherein each one of the plurality of nozzle vanes has a leading edge and a trailing edge, the leadIng edge having a first bow angle and the trailing edge having a second bow angle, wherein each one of the plurality of nozzle vanes is bowed uniformly between the leading edge and the trlallng edge.

Also, the stator as above, whereIn the first and second bow angles are between about 20 degrees and about 40 degrees, and/or wherein the first and second bow angles are between about 27 degrees and about 33 degrees.

[00311 The foregoing has also described an exemplary stage for a turbomachine comprising a rotor dIsposed about a shaft of the turbomachlne, operatively engaging the shaft, and configured to rotate in a circumferentIal dIrection, the rotor having a plurality of blades; and a stator in fluid communIcation with the rotor, located axially adjacent to the rotor, and comprising: a plurality of nozzle vanes spaced circumferentlally apart to channel a workIng fluid therebetween, and bowed to create bowed wakes In the worldng fluid, whereIn the bowed wakes are configured to engage the plurality of blades incrementally. Further described Is the stage as above, wherein the stator further comprises: an Interior circumferential surface; and an exterior circumferential surface spaced radIally outward from the interior circumferential surface, wherein the plurality of nozzle vanes extend radIally between the Interior circumferential surface and the exterior circumferential surface, wherein each one of the plurality of nozzle vanes defines a hub where each one of the plurality of nozzle vanes meets the interior circumferential surface and a tip where each one of the plurality of nozzle vanes meets the exterior circumferential surface. Also described is the stage as above, wherein each one of the plurality of nozzle vanes Is bowed between the hub and the tip at least In the circumferential direction and/or whereIn each one of the plurality of nozzle vanes is bowed between the hub and the tip in the circumferentIal direction and in an axial direction.

Additionally, the stage as above, wherein each one of the plurality of nozzle vanes has a leading edge defining an upstream axial extremity of each one of the plurality of nozzle vanes, s. ..--. --.-. .---. **-*..:. . wherein the leading edge Is bowed to define a first bow angle, and/or wherein the first bow angle is between about 25 degrees and about 35 degrees. Additionally described is the stage as above, wherein each one of the plurality of nozzle vanes has a trailing edge defining a downstream axial extremity of each one of the plurality of nozzle vanes, wherein the trailing edge is bowed to define a second bow angle, the second bow angle being between about 20 degrees and about 40 degrees. Also described is the stage as above, wherein the second bow angle Is between about 25 degrees and about 35 degrees, and/or wherein the first and second bow angles are about equal and between about 27 degrees and about 33 degrees.

Further described Is the stage as above, wherein each one of the plurality of nozzle vanes Is bowed uniformly between the leading and the trailing edges, and/or wherein each one of the plurality of nozzle vanes has a mid-span and the first and second bow angles are distributed to the mid-span, and/or whereIn: the first bow angle has a first axial component and a first circumferential component; and the second bow angle has a second axial component and a second circumferential component, wherein the second axial component is greater than the first axial component Also described is the stage as above, wherein each one of the plurality of nozzle vanes Is curved from the leading edge to the trailing edge to channel the working fluid.

[0032J The foregoing has outlined features of several embodiments so that those skilled In the art may better understand the detailed description that follows. Those skilled In the art should apprecIate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for canylng out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled In the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the present disclosure.

Claims (20)

1. -..--*. *s*_.. ...... . . Claims We Claim: 1. A stator hr a turbomachine comprising: an Interior circumferential surface; an exterior circumferential surface spaced radially apart from the Interior circumferential surface; and a plurality of nozzle vanes extending between the Interior and exterior circumferential surfaces, spaced circumferentlalty apart to channel a worldng fluid therebetween, and bowed to create bowed wakes In the working fluid, the bowed wakes being configured to Incrementally engage blades of the turbomachine.
2. 2. The stator of claIm 1, whereIn the plurality of nozzle vanes are bowed In an axial direction and In a circumferential direction.
3. 3. The stator of claim 2, whereIn the plurality of nozzle vanes are bowed in a spanwise distribution.
4. 4. The stator of claimS, wherein the plurality of nozzle vanes are bowed symmetrically to a mid-span.
5. 5. Thestatorofclaiml,whereln: each one of the plurality of nozzle vanes has a leading edge and a trailing edge, the leading edge having a first bow angle and the trailing edge having a second bow angle; and each one of the plurality of nozzle vanes Is bowed uniformly between the leading edge and the trailing edge.
6. 6. The stator of claim 5, whereIn the first and second bow angles are each between about degrees and about 35 degrees.
7. 7. The statorof claims, wherein the first and second bow angles are each between about 27 degrees and about 33 degrees.
8. 8. A stage for a turbomachine, comprising: a rotor disposed about and operative engaging a shaft of the turbomachine, the rotor having a plurality of blades and being configured to rotate in a circumferential direction; and a stator in fluid communication with the rotor, located axially adjacent to the rotor, and comprising a plurality of nozzle vanes spaced circumferentially apart to channel a working fluid therebetween, the plurality of nozzle vanes each being bowed to create bowed wakes in the working fluid, wherein the bowed wakes are configured to engage the plurality of blades incrementally.
9. 9. The stage of claim 8, wherein the stator further comprises: an interior circumferential surface; and an exterior circumferential surface spaced radially outward from the interior circumferential surface, wherein the plurality of nozzle vanes extend radially between the interior circumferential surface and the exterior circumferential surface, and wherein each one of the plurality of nozzle vanes defines a hub where each one of the plurality of nozzle vanes meets the interior circumferential surface and a tip where each one of the plurality of nozzle vanes meets the exterior circumferential surface.
10. 10. The stage of claim 9, wherein each one of the plurality of nozzle vanes is bowed between the hub and the tip at least in the circumferential direction.
11. 11. The stage of claim 10, wherein each one of the plurality of nozzle vanes is bowed between the hub and the tip in an axial direction.
12. 12. The stage of claim 8, wherein each one of the plurality of nozzle vanes has a leading edge defining an upstream axial extremity of each one of the plurality of nozzle vanes, the leading edge being bowed to define a first bow angle of between about 20 degrees and about degrees.
13. 13. The stage of claim 12, wherein the first bow angle is between about 25 degrees and about 35 degrees.
14. 14. The stage of claim 12, wherein each one of the plurality of nozzle vanes has a trailing edge defining a downstream axial extremity of each one of the plurality of nozzle vanes, the trailing edge being bowed to define a second bow angle of between about 20 degrees and about 40 degrees.
15. 15. The stage of claim 14, wherein the second bow angle is between about 25 degrees and about 35 degrees.
16. 16. The stage of claim 14, wherein the first and second bow angles are about equal and between about 27 degrees and about 33 degrees.
17. 17. The stage of claim 16, wherein each one of the plurality of nozzle vanes is bowed uniformly between the leading and the trailing edges.
18. 18. The stage of claim 14, wherein each one of the plurality of nozzle vanes has a mid-span and the first and second bow angles are distributed to the mid-span.
19. 19. The stage of claim 14, wherein: the first bow angle has a first axial component and a first circumferential component; and the second bow angle has a second axial component and a second circumferential component, the second axial component being greater than the first axial component.
20. 20. The stage of claim 14, wherein each one of the plurality of nozzle vanes is curved from the leading edge to the trailing edge to channel the working fluid.