Gas turbine compressor stator blade

Abstract

A stator assembly of an axial flow compressor includes removable stator blades that slidably engage within a circumferential channel formed along the inside surface of a circular compressor casing. The channel forms a circle around the rotational axis of the turbine about which the compress casing is positioned. Thus, the curvature of the channel coincides with the radial distance of the channel from the center of the casing and thus also from the rotational axis of the turbine. Grooves are undercut in the casing to extend along each side of the channel to slidably receive rails that extend along the sides of the base of the stator blades.

Description

BACKGROUND

[0001] The present application pertains to a stator assembly for an axial compressor of a turbine engine, including a gas turbine, as well as replaceable individual blades for the stator assembly. The stator assembly composed of individual blades creates a stage of the axial flow compressor.

[0002] Referring to FIGS. 1A and 1B, the blades 10 for the stator assembly 12 forming a stage of an axial flow compressor of a gas turbine engine consist of a base 14 that is mounted within a compressor casing 16 that extends circumferentially within a turbine housing 18 so that the airfoil portion 20 of the stator blade 10 projects from the base 14 toward the rotational center of the gas turbine engine. A circumferential channel 22 is formed in the casing 16 to receive the base 14. Rails 24 extend long, and project form, the sides of the blade base 14 to be slidably receivable within undercut grooves 26 that extend along the sides of the channels 22. This is known as a “hook fit” assembly or arrangement. As with the channel 22, the undercut grooves 26 are circumferential relative to the rotational axis of the gas turbine engine. Both the channels 22 and undercut grooves 26 are precision machined.

[0003] The blades 10 are disposed in the circumferential channel 22 so that the bases 14 are end-to-end to each other, as shown in FIG. 1A. Further by this assembly arrangement, the blades 10 are meant to be replaceable.

[0004] In existing stator assemblies, the bottom 28 of the stator blade base 14 is flat, and the ends 30 of the base are perpendicular (90 degrees) to the base 14. As such, there is a gap D1 (for example 0.022 inches) between the bottom of the stator base 28 and the channel 22. Also, as such, the bases of adjacent blades 10 make contact with each other at the upper corners 32 of the ends 30 at an elevation D2 below the upper surface of the undercut groove 26. As a consequence, an angle A1 / A2 exists between the ends 30 of the adjacent blades. Also, the rails 24 are parallel to the bottom 28 of the base 14, so the gap D1 also exists between the underside of the rails and the channel 22.

[0005] During operation of the turbine engine, due to air flow against the air foils 20, as shown by the arrow in FIG. 4, the blades 10 are allowed to move the channels 22, and the stator blades 10 are loaded in the radially outward direction relative to the rotational axis of the turbine engine seeking to press the stator blade bases 14 into the circumferential channels 22. Likewise, the bottoms 34 of the blade rails 24 load against the adjacent portion of the undercut grooves 26. As such, due to the “straight cut of the rails 24,” at the ends of the blade rails 24, the bottom corners 36 impart a high point load on the adjacent portion of the undercut groove 26 of the which is circumferential in shape. Over time, the groove 26 of the compressor casing 16 is worn down by the blade rails 24, in particular by the bottom corners 36, causing the excess clearance and looseness between the stator blades 10 and compressor casing 16. This wear is known as “blade rock.”

[0006] Also, the blades 10 twist due to the load from the air flow of the airfoils 20 as the base 14 becomes looser in the casing channel due to the wear of the casing caused by the point loads imposed by the rails 24. As the blades 10 continue to rock and twist during operation of the gas turbine engine, the ends 30 of the blade bases 14 also wear. As such, the excessing clearance occurs between the stator blades 10 and their “fit” with the compressor casing 16 thereby requiring repairs to the stator assembly 12. Also the ends 30 wear at point 32 thereby causing total circumferential distance of the assemble blades 10 to decreased from the assembled specification. This specification is known as “blade drop” and is established during assembly.

[0007] Repairs to stator blade 10 point loading and twisting can be completed using standard practices. A first option is total replacement of the compressor case or casings. This is very expensive. A second option is to machine out the worn undercut groove 26 portion of the compressor casing 16 and install a section of the casing with the undercut groove 26. This is known as a “patch ring”. This can be completed in a field machining operation or by removing the casing and is completed at a large machine shop.

[0008] A third option is to replace the existing stator blades 10 with new stator blades 10. If the blades are replaced with original straight rails and 90° end faces 30 of the blade base 14, a slight improvement is usually achieved which may be enough to return the blade to original tolerance conditions. However, this repair only lasts a limited time because the blade is still in the point loaded condition on both the ends of the rails 24 and the top corners of the faces 30.

[0009] The present disclosure seeks to address the shortcomings of existing compressor stator assemblies.SUMMARY

[0010] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0011] In accordance with one embodiment of the present disclosure, a stator blade is provided for installation in the cylindrical casing of a compressor for a turbine, the casing having a circumferential channel disposed about the rotational axis of the turbine for receiving the stator blade and having undercut circumferential grooves extending into the casing along opposite sides of the channel. The stator blade includes a base comprising a first surface and opposite sides and opposite ends, the base being sized and shaped to be engageable in the casing channel; an airfoil projecting from the first surface of the base; and rails extending along and projecting outwardly from the sides of the base, the rails being sized to be closely receivable within the grooves and curved in the circumferential direction of the grooves to correspond to the circumferential curvature of the grooves.

[0012] In any of the embodiments described herein, wherein the rails are of a thickness closely corresponding to the height of the grooves.

[0013] In any of the embodiments described herein, wherein the base comprises a second surface opposite to the first surface, and the rails extend along the second surface of the base.

[0014] In any of the embodiments described herein, wherein the second surface of the base is curved about the center of the casing to coincide with the curvature of the rails.

[0015] In any of the embodiments described herein, wherein the curvature of the rails coincides with their radial distance for the rotational axis of the turbine.

[0016] In any of the embodiments described herein, wherein the first surface of the base is curved about the rotational axis of the turbine.

[0017] In any of the embodiments described herein, wherein curvature of the first surface of the base about the rotational axis of the turbine coincides with the radial distance of the first surface from the rotational axis of the turbine.

[0018] In any of the embodiments described herein, wherein the opposite ends of the base being disposed at an angle with each other to engage in face-to-face abutment with the end of an adjacent stator blade base when installed in the casing.

[0019] In any of the embodiments described herein, wherein the opposite ends of the base being in radial alignment with the rotational axis of the turbine.

[0020] In accordance with another embodiment of the present disclosure, a stator assembly for a turbine is provided, the turbine having a longitudinal rotational axis. The stator assembly includes a cylindrical casing disposable concentrically with the turbine longitudinal rotational axis, the casing having a circumferential channel extending along the inside surface of the casing and undercut circumferential grooves extending into the casing along opposite sides of the channel; a stator blade comprising a base comprising a first surface and opposite sides and opposite ends, the base being sized and shaped to be engageable in the casing channel; an airfoil projecting from the first surface of the base; and rails extending along and projecting outwardly from the sides of the base, the rails being sized to be closely receivable within the grooves and curved along their lengths to correspond to the circumference of the grooves.

[0021] In any of the embodiments described herein, wherein the rails are of a thickness closely corresponding to the height of the grooves.

[0022] In any of the embodiments described herein, wherein the base comprises a second surface opposite to the first surface, and the rails extend along the second surface of the base.

[0023] In any of the embodiments described herein, wherein the second surface of the base is curved about the rotational axis of the turbine to coincide with the curvature of the rails.

[0024] In any of the embodiments described herein, wherein the curvature of the rails coincides with their radial distance from the longitudinal rotational axis of the turbine.

[0025] In any of the embodiments described herein, wherein the first surface of the base is curved about the rotational axis of the turbine.

[0026] In any of the embodiments described herein, wherein curvature of the first surface of the base about the rotational axis of the turbine coincides with the radial distance of the first surface from the longitudinal rotational axis of the turbine.

[0027] In any of the embodiments described herein, wherein the opposite ends of the base are disposed at an angle with each other to engage in face-to-face abutment with the end of an adjacent stator blade base when installed in the casing.

[0028] In any of the embodiments described herein, wherein the opposite ends of the base are in radial alignment with the longitudinal rotational axis of the turbine.DESCRIPTION OF THE DRAWINGS

[0029] The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:

[0030] FIG. 1A is an enlarged fragmentary view of an existing compressor stator assembly;

[0031] FIG. 1B further enlarged portion of the indicated portion of FIG. 1A;

[0032] FIG. 2A is a view similar to FIG. 1A, but depicting the compressor stator assembly of the present disclosure;

[0033] FIG. 2B is a further enlarged portion of the indicated portion of FIG. 2A;

[0034] FIG. 3A is a pictorial view of a stator blade of the present disclosure;

[0035] FIG. 3B is a top or plan view of FIG. 3A;

[0036] FIG. 3C is a side elevational view of FIG. 3A;

[0037] FIG. 3D is an end elevational view of FIG. 3A;

[0038] FIG. 4 is a pictorial view of the lower half of a stator assembly and showing how the stator blades are engaged with the stator casing.DETAILED DESCRIPTION

[0039] Various example embodiments of the present disclosure are described below with reference to the accompanying drawings in which some example embodiments are illustrated. In the figures, the thicknesses of lines, layers and / or regions may be exaggerated for clarity.

[0040] While example embodiments are capable of various modifications and alternative forms, embodiments thereof are shown by way of example in the figures and are described in detail below. It should be understood, however, that there is no intent to limit example embodiments to the particular forms disclosed, but on the contrary, example embodiments are to cover all modifications, equivalents, and alternatives falling within the scope of the disclosure.

[0041] It is understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,”“adjacent” versus “directly adjacent,” etc.).

[0042] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a,”“an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,”“comprising,”“includes” and / or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0043] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, e.g., those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art. However, should the present disclosure give a specific meaning to a term deviating from a meaning commonly understood by one of ordinary skill, this meaning is to be considered in the specific context this definition is given herein.

[0044] In the following description, numerous specific details are set forth in order to provide a thorough understanding of exemplary embodiments of the present disclosure. It will be apparent to one skilled in the art, however, that many embodiments of the present disclosure may be practiced without some or all of the specific details. Further, it will be appreciated that embodiments of the present disclosure may employ any combination of features described herein.

[0045] The present application may include references to directions, such as “forward,”“rearward,”“front,”“back,”“ahead,”“behind,”“upward,”“downward,”“above,”“below,”“top,”“bottom,”“right hand,” left hand,”“in,”“out,”“extended,”“advanced,”“retracted,”“proximal,”“distal,”“central,”“vertical,” etc. These references and other similar references in the present application are only to assist in helping describe and understand the present invention and are not intended to limit the present invention to these directions or locations.

[0046] The present application may also reference quantities and numbers. Unless specifically stated, such quantities and numbers are not to be considered restrictive, but exemplary of the possible quantities or numbers associated with the present application. Also, in this regard, the present application may use the term “plurality” to reference a quantity or number. In this regard, the term “plurality” is meant to be any number that is more than one, for example, two, three, four, five, etc.

[0047] The present application may include modifiers such as the words “generally,”“approximately,”“about”, or “substantially.” These terms are meant to serve as modifiers to indicate that the “dimension,”“shape,”“temperature,”“time,” or other physical parameter in question need not be exact, but may vary as long as the function that is required to be performed can be carried out. For example, in the phrase “generally circular in shape,” the shape need not be exactly circular as long as the required function of the structure in question can be carried out. If a quantitative value is needed to render the applicable parameter sufficiently definite, the applicable parameter is within five percent (5%) of the designated parameter value.

[0048] Referring initially to FIGS. 2A and 4, the present disclosure pertains to a compressor stator assembly 112 essentially consisting of removable stator blades 100 that slidably engage within a circumferential channel 122 formed along the inside surface of a circular compressor casing 116, the lower half which is shown in FIG. 4. The compressor stator assembly 112 with the individual stator blades 100 forms a stage in an axil flow compressor for a gas turbine engine. The channel 122 forms a circle around the rotational axis of the turbine about which the compress casing is positioned. Thus, the curvature of the channel 122 coincides with the radial distance of the channel from the center of the casing 116 and thus also from the rotational axis of the turbine.

[0049] When the stator blades 100 are fully assembled within the channel, a small gap, know as the “blade drop,” is provided between the upper most stator blade and the end, horizontal surface 117 of the compressor casing 116. This gap is needed to allow for the expansion of the bases of 114 of the stator blades 100 due to heat occurring during the operation of the gas turbine engine in which the stator assembly 112 is assembled.

[0050] Additionally referring to FIGS. 2B-3D, the stator blade 110 includes an air foil 120 that projects from the upper surface 138 of the blade base 114. As shown in FIGS. 3A and 3B, the air foil 120 includes a curved surface 140 and a substantially straight surface 142 extending from the nose or leading edge 144 to the trailing edge 146. As is typical, the distance between the leading edge 144 and trailing edge 146 decreases somewhat as the air foil extends further away from the blade base 114, resulting in a slightly taper profile, see FIG. 3A.

[0051] The stator blade base 114 is generally rectangular in shape, but with the bottom surface of 128 the blade base not straight but rather curved to match the curvature of the circumferential channel 122 of the compressor casing 116 in the direction extending along the circumference of the channel 122. See FIGS. 2A and 2B. As will be appreciated, in this manner the curvature of the bottom surface of the base coincides with the radial distance of the base from the center of the compressor casing 116 when the blade 110 is installed in the casing and thus also the rotational axis of the gas turbine.

[0052] Although not essential, the first or upper surface 138 of the stator blade base 114 can be curved to match the curvature of the circumferential channel 122 of the compressor casing 116, see FIGS. 2A and 2B. In this manner, the curvature of the upper surface can be the same or substantially the same as the curvature of the bottom surface 128 along the circumference of the channel 122.

[0053] Rails 124 extend along the lower portion of the two sides of the base 114 and outwardly of the base. The rails are shaped and sized to be slidably receivable within grooves 126 that are undercut in the compressor casing 116 along each side of the circumferential channel 122. The grooves 126 can be located at the base of the circumferential channel 122 or located above the base of the circumferential channel 122.

[0054] The rails 124 are curved along their length to match the curvature of the undercut grooves 126. Thus, as with the channel 122, the curvature of the rails 124 is based on the radial distance of the rails from the center of the casing 116 and thus also the radial distance from the rotational axis of the turbine engine. In this manner, the lower surfaces of the rails 124 bear against the bottom of the undercut grooves 126 for the full length of the rails. As such, wear of the grooves 126 by the ends 113 of the rails 124 is substantially reduced relative to the wear caused by the straight rails as discussed herein.

[0055] Although not essential, the bottom surfaces 134 of the rails 124 are shown to match the bottom surface 128 of the base 114. Typically, this facilitates the manufacture of the stator base 114 and the corresponding rails 124.

[0056] The thickness T of the rails 124 is slightly less than the height H of the of the undercut grooves 126, see FIG. 2B. Typically, a clearance of about 0.010″ inch is provided between thickness of the rails 124 and the height of the undercut grooves 126. This clearance is less that needed when straight rails are used.

[0057] The ends 130 of the base 114 are not parallel to each other, rather the ends 130 extend along a radial line coinciding with the center of the compressor casing 116 which also coincides with the rotational center of the gas turbine engine. As such, when the stator blades 110 are disposed end to end as shown in FIGS. 2A, 2B, and 4, the ends 130 of the bases 114 of adjacent stator blades, being in radial alignment with the center of the compressor casing 116, are in full face-to-face contact with each other, and not at a point-to-point contact in the manner discussed herein with respect to existing stator blades 110.

[0058] It will be appreciated that with the full face-to-face contact of the ends 130 of the stator blade bases 114 and the base rails 124 being curved to match the curvature of the undercut grooves 126, the point loading of the bases on the grooves 126 and the point loading of the bases 114 on each other is eliminated or at least greatly reduced. As such, blade rock is also substantially reduced, thereby reducing the frequency of the needed repair and / or replacement of the compressor casing 116 and the stator blades 110.

[0059] While illustrative embodiments have been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention. In this regard, the present disclosure has been described in conjunction with a gas turbine engine; however, the present disclosure can be used in conjunction with other types of turbines.

Claims

1. A stator blade for installation in the cylindrical casing of a compressor for a turbine, the casing having a circumferential channel disposed about the rotational axis of the turbine for receiving the stator blade and having undercut circumferential grooves extending into the casing along opposite sides of the channel, the stator blade comprising:a. a base comprising a first surface and opposite sides and opposite ends, the base being sized and shaped to be engageable in the casing channel, wherein the opposite ends of the base are disposed at an angle with each other to engage in face-to-face abutment with the end of an adjacent stator blade base when installed in the casing;b. an airfoil projecting from the first surface of the base; andc. rails extending along and projecting outwardly from the sides of the base, the rails being sized to be receivable within the grooves and curved in the circumferential direction of the grooves to correspond to the circumferential curvature of the grooves, wherein the face-to-face abutment of the base is configured to prevent wear of the casing.

2. The stator blade of claim 1, wherein the rails are of a thickness corresponding to the height of the grooves.

3. The stator blade of claim 1, wherein the base comprises a second surface opposite to the first surface, and the rails extend along the second surface of the base.

4. The stator blade of claim 3, wherein the second surface of the base is curved about the center of the casing to coincide with the curvature of the rails.

5. The stator blade of claim 4, wherein the curvature of the rails is located at their distal radial distance from the rotational axis of the turbine.

6. The stator blade of claim 1, wherein the first surface of the base is curved about the rotational axis of the turbine.

7. The stator blade of claim 6, wherein curvature of the first surface of the base about the rotational axis of the turbine is located at the distal radial distance of the first surface from the rotational axis of the turbine.

8. (canceled)9. The stator blade of claim 8, wherein the opposite ends of the base being in radial alignment with the rotational axis of the turbine.

10. A stator assembly for a turbine, the turbine having a longitudinal rotational axis, the stator assembly comprising:a. a cylindrical casing disposable concentrically with the turbine longitudinal rotational axis, the casing having a circumferential channel extending along the inside surface of the casing and undercut circumferential grooves extending into the casing along opposite sides of the channel,b. a stator blade comprising:i. a base comprising a first surface and opposite sides and opposite ends, the base being sized and shaped to be engageable in the casing channel, wherein the opposite ends of the base are disposed at an angle with each other to engage in face-to-face abutment with the end of an adjacent stator blade base when installed in the casing;ii. an airfoil projecting from the first surface of the base; andiii. rails extending along and projecting outwardly from the sides of the base, the rails being sized to be receivable within the grooves and curved along their lengths to correspond to the circumference of the grooves, wherein the opposite ends of the base are disposed at an angle with each other to engage in face-to-face abutment with the end of an adjacent stator blade base when installed in the casing, wherein the face-to-face abutment of the base is configured to prevent wear of the casing.

11. The stator assembly of claim 10, wherein the rails are of a thickness corresponding to the height of the grooves.

12. The stator assembly of claim 10, wherein the base comprises a second surface opposite to the first surface, and the rails extend along the second surface of the base.

13. The stator assembly of claim 12, wherein the second surface of the base is curved about the rotational axis of the turbine to coincide with the curvature of the rails.

14. The stator assembly of claim 13, wherein the curvature of the rails is located at their distal radial distance from the longitudinal rotational axis of the turbine.

15. The stator assembly of claim 10, wherein the first surface of the base is curved about the rotational axis of the turbine.

16. The stator assembly of claim 15, wherein curvature of the first surface of the base about the rotational axis of the turbine is located at the distal radial distance of the first surface from the longitudinal rotational axis of the turbine.

17. (canceled)18. The stator assembly of claim 17, wherein the opposite ends of the base are in radial alignment with the longitudinal rotational axis of the turbine.

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