Stator Assembly

Abstract

A stator assembly for a compressor includes a plurality of circumferentially spaced apart vanes positively retained at the outer radial ends by engagement within a split casing wherein the vanes further include root portions at their inner radial ends for respective engagement within pocket formed around an inner segmented shroud member.

Description

The invention herein described was made in the course of or under a contract or subcontract thereunder (or grant) with the Department of the Air Force.

BACKGROUND OF THE INVENTION

This invention relates to a stator vane assembly and, more particularly, to a stator vane assembly for an axial flow compressor wherein a plurality of axially spaced apart rows of stator vanes having inner shrouds are interdigitated between a plurality of axially spaced apart rows of rotor blades.

In axial flow compressors, which may be of the type commonly utilized in gas turbine engines, there is generally included a rotor from which extend a number of axially spaced apart rows of rotor blades. Rows of axially spaced apart stator vanes are also provided and extend radially inward from the compressor casing between the rows of rotor blades. In order to prevent airflow leakage around each row of stator vanes, there is generally included an inner shroud which is retained at the inner radial ends of each row of stator vanes. Each shroud is supported entirely by a row of stator vanes and may be arranged to sealingly engage a plurality of revolving teeth formed integral to the compressor rotor.

Difficulty may arise as a direct result of the means utilized to fasten the inner shroud to the stator vanes. In the past, it has often been necessary to use retaining bolts or clips which may loosen during engine operation and thereby enter the compressor flowpath, causing severe damage. In a gas turbine engine, the use of retaining bolts or clips further adds to the weight of the compressor and thereby reduces the overall thrust to weight ratio of the engine. Also, it has generally been necessary to make shrouds from metal which again unduly adds to the weight of the compressor.

Therefore, it is a primary object of this invention to provide a stator vane assembly wherein the inner shroud may be readily fastened to the inner radial ends of the stator vanes without the use of retaining bolts or clips.

It is a further object of this invention to provide a stator vane assembly wherein the inner shroud may be molded from a lightweight plastic in order to reduce the overall weight of the compressor.

SUMMARY OF THE INVENTION

A stator assembly includes an outer casing longitudinally split into at least two sectors wherein each sector has a dovetail groove around the inside surface thereof. There is also included an inner segmented shroud longitudinally split into at least two sectors, each of which has a plurality of circumferentially spaced apart pockets in the outer surface thereof wherein each pocket is undercut at one end. A plurality of stator vanes extends radially between the shroud and casing with each vane having an inner root portion which includes an integral heel portion and an integrally extending toe portion for engaging the undercut end of a respective shroud pocket. Each vane also includes an outer platform from which extend forward and aft tangs which engage the dovetail groove.

DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims distinctly claiming and particularly pointing out the invention described herein, it is believed that the invention will be more readily understood by reference to the discussion below and the accompanying drawings in which:

FIG. 1 is a side view, partly in cross-section, of a gas turbine engine embodying the stator assembly of this invention.

FIG. 2 is a cross-sectional view of a portion of a compressor embodying the stator assembly of this invention.

FIG. 3 is a cross-sectional view taken along the line 3--3 in FIG. 2.

FIG. 4 is an enlarged cross-sectional view taken along the line 4--4 in FIG. 3.

FIG. 5 is a cross-sectional view taken along the line 5--5 of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, there is shown a gas turbine engine 10 having an outer casing 12 open at one end to provide an inlet 14. Ambient air enters the inlet 14 and is compressed by a compressor 16 which may be of the axial flow type. Compressor 16 includes a rotor 18 from which extend a number of axially spaced apart rows of rotor blades 20 interdigitated between rows of axially spaced apart stator vanes 22. Pressurized air is discharged from the compressor 16 through a plurality of circumferentially spaced apart outlet guide vanes 24 whereupon the compressed air is diffused prior to entering a combustion chamber 26. Combustion chamber 26 is defined by a combustion liner 28 and receives an inlet flow of fuel through a plurality of circumferentially spaced apart fuel nozzles 30. The high pressure air and fuel mixture is ignited to produce a high energy gas stream which exits from the combustion chamber 26 through a nozzle diaphragm 32. High energy gas from the nozzle diaphragm 32 drives a turbine 34 which connects to the compressor rotor 18 through a shaft 36. It will thus be appreciated that the gas turbine engine 10 so far described could be utilized as a gas generator in combination with a power turbine (not shown) to form either a turboprop, turbofan or a turboshaft engine in a manner well known to the gas turbine art. Within the engine 10 there is also disclosed a frame 38 within which the shaft 36 is journalled for rotation by a forward bearing 40 and aft bearing 40'.

As best seen by referring to FIG. 5, casing 12 is longitudinally split along two 180.degree. sectors which are connected by a plurality of axially spaced apart locking bolts 13. Locking bolts 13 pass through aligned holes in two pairs of integral flanges 15, 15' and 17, 17' which are spaced 180.degree. apart around the compressor casing 12. Lock nuts 13' may be provided to threadably engage lock bolts 13.

Referring now to FIG. 2, there is shown a portion of the compressor 16 including a forward rotor disc 42 and an aft rotor disc 44, both of which are interconnected to simultaneously rotate as an integral part of the compressor rotor 18. It should be readily appreciated that the compressor rotor 18 may include more or less rotor discs depending upon the specific design requirements of the gas turbine engine 10. A plurality of circumferentially spaced apart blades 20 are disposed about the periphery of the forward rotor disc 42 wherein each blade 20 includes a root portion 46 for attachment to the rotor disc 42 as is well known to the compressor art. In like manner, a plurality of circumferentially spaced apart blades 20' are also disposed about the periphery of the aft rotor disc 44 wherein each blade includes a root portion 48 for attachment to the rotor disc 44. In order to prevent air flow leakage around the blades 20 and 20', the outer tips of the blades are respectively circumscribed by shrouds 50 and 52, which may be of the honeycomb type.

Intermediate the forward rotor disc 42 and aft rotor disc 44, there is provided a row of circumferentially spaced apart stator vanes 22, each of which includes an outer platform 66, from which extend forward and aft tangs 68, 68', which engage a dovetail groove 70 around the inner surface of the casing 12. In order to prevent air flow leakage around the stator vanes 22, there is provided an inner segmented shroud 56 which may operate as the stator member of a labyrinth type seal by engaging a plurality of revolving teeth 57 formed integral to the compressor rotor 18. Each stator vane 22 includes a root portion 54 formed in the manner of a foot so as to have an integral heel portion 58 together with an integrally extending toe or tang portion 60. Shroud 56 includes a plurality of circumferentially spaced apart pockets 62 which are undercut on one end 64 to accommodate insertion of the individual root portions 54.

Referring now to FIG. 4, the manner of insertion for each individual root portion 54 within a corresponding pocket 62 may be more readily understood. Each stator vane 22 is first tipped or rotated in relation to the center axis of the shroud in order to insert the tang portion 64 of the root 54 into the pocket 62 so as to engage the undercut surface 64 as illustrated by the phantom lines. Each stator vane 22 is then rotated about the undercut surface 64 so as to bring the heel portion 58 of the root 54 into engagement with the pocket 62. The fit between the root 54 and pocket 62 may have a controlled clearance upon full engagement of the root within the pocket.

Referring now to FIG. 5, it can be seen that the inner shroud 56 has also been longitudinally split into two 180.degree. sectors. In order to assemble engine 10, individual stator vanes 22 are first inserted into respective pockets 62 in the inner shroud segments 56. Once the stator vanes 22 have been arranged in circumferentially spaced apart relation by insertion within respective pockets 62 in shroud segments 56, each shroud segment, together with its associated stator vanes, is then slid circumferentially into engagement with the dovetail groove 70 in casing 12. As is readily apparent, splitting the casing 12 provides access to the dovetail groove 70, thereby permitting circumferential insertion of the individual stator vane outer platforms 66 within the dovetail groove. Once all the stator vane outer platforms 66 have been inserted within the dovetail groove 70, it will be appreciated that the inner segmented shroud 56 is positively restrained from detaching from the stator vane root portions 54. In order for the shroud 56 to detach from the stator vane root portions 54 it would be necessary for all the stator vanes 22 to simultaneously rotate about a plane normal to the center axis of the shroud 56. As is readily apparent, however, the dovetail groove 70 prohibits simultaneous rotation of the stator vane outer platforms 66 and thereby positively precludes detachment of the inner shroud segments 56 from the stator vanes 22 after insertion within the dovetail groove 70. As is readily apparent, the shroud 56 may be made relatively thin and lightweight and still remain radially constrained for close clearance with the rotor 18. In addition, the shroud 56 positively engages the inner radial ends of the stator vanes 22 constraining the stator vanes from rotating or flexing about their radial axes. Once the individual sectors have been assembled, as shown in FIG. 5, it is a simple matter to insert locking bolts 13 through flanges 15, 15' and 17, 17' respectively in order to connect the two casing sectors.

The engine 10 may be disassembled by reversing the above described process. First the connecting bolts 13 are loosened in order to separate the two sectors of the engine casing 12. Then the stator vane outer platforms 66 are circumferentially slid out of engagement with the dovetail groove 70, after which each stator vane 22 may be rotated out of engagement with its respective shroud pocket 62. Although the inner shroud 56 has been illustrated in two 180.degree. segments, it is to be understood that the arc length of each shroud is not so limited and may, in fact, be less than 180.degree.. Of particular advantage is the ease of assembly for the segmented shroud 56 which may be fastened to the stator vanes 22 without additional hardware such as locking bolts and nuts. Such hardware unduly adds to the weight of the engine and may loosen during engine operation, damaging other compressor components. The segmented shroud 56 may also be produced economically by injection molding wherein the molded segments may be formed of lightweight plastic.

Thus having described a preferred embodiment of the invention, though not exhaustive of all possible equivalents, what is desired to be secured by Letters Patent is claimed below.

Claims

What is claimed is:

1. A stator assembly comprising:

an outer casing longitudinally split into at least two sectors and having a dovetail groove around the inside surface thereof;

an inner segmented shroud longitudinally split into at least two sectors, each of which has a plurality of circumferentially spaced apart pockets in the outer surface thereof wherein each pocket is undercut at one end, and

a plurality of stator vanes extending radially between the shroud and casing with each vane having:

an inner root portion which includes an integral heel portion and an integrally extending toe portion for engaging the undercut end of a respective shroud pocket, and an outer platform from which extend forward and aft tangs which engage the dovetail groove.

2. The stator assembly of claim 1 wherein the shroud is plastic.

3. The stator assembly of claim 1 wherein the casing is longitudinally split along two 180.degree. sectors and the sectors are connected by a plurality of axially spaced apart locking bolts which pass through aligned holes in two pairs of integral flanges which are spaced 180.degree. apart around the casing.

4. The stator assembly of claim 1 wherein each stator vane may be individually inserted into a respective pocket in the shroud by first rotating the stator vane in relation to the center axis of the shoud in order to insert the tang portion of the root into the pocket so as to engage the undercut surface whereupon the stator vane may be rotated about the undercut surface so as to bring the heel portion of the root into engagement with the pocket.

5. A compressor comprising:

an outer casing longitudinally split into at least two sectors and having at least one dovetail groove around the inside surface thereof;

a rotor from which extend at least two axially spaced apart rows of rotor blades;

at least one inner segmented shroud longitudinally split into at least two sectors which are interposed between two rows of rotor blades wherein the sectors each include a plurality of circumferentially spaced apart pockets in the outer surface thereof, each of which is undercut at one end, and a plurality of stator vanes extending radially between the shroud and casing with each vane having:

an inner root portion including an integral heel portion and an integrally extending toe portion for engaging the undercut end of a respective shroud pocket, and an outer platform from which extend forward and aft tangs which engage the dovetail groove.

6. The compressor of claim 5 wherein the shroud in plastic.

7. The compressor of claim 5 wherein the casing is longitudinally split along two 180.degree. sectors and the sectors are connected by a plurality of axially spaced apart locking bolts which pass through aligned holes in two pairs of integral flanges which are spaced 180.degree. apart around the compressor casing.

8. The compressor of claim 5 wherein each stator vane may be individually inserted into a respective pocket in the shroud by first rotating the stator vane in relation to the center axis of the shroud in order to insert the tang portion of the root into the pocket so as to engage the undercut surface whereupon the stator vane may be rotated about the undercut surface so as to bring the heel portion of the root into engagement with the pocket.

9. The compressor of claim 5 wherein the inner shroud operates as the stator member of a labyrinth type seal by engaging a plurality of revolving teeth formed integral to the compressor rotor.