Two-piece Channel Diffuser

Abstract

A channel diffuser for a centrifugal compressor in which the diffuser is formed from two annular elements, sandwiched together. One element is a flangelike portion of the outer housing for an engine and has a smooth radially extending face. The second element has a series of tangentially directed channels open toward the radial face on the first element to form diffuser passages. The channels in the second element diverge both in width and in height so that all the divergence in the passages is provided by the channels.

Description

The present invention relates to compressor diffusers and more particularly to compressor diffusers for radial-type compressors.

One of the most important components of a centrifugal compressor is the fixed diffuser section which receives the high velocity air discharged from a rotating impeller. This component is designed to diffuse the high velocity and increase its static pressure to a level suitable for use in the combustor of a gas turbine. Many different aerodynamic configurations have been proposed and adopted in the past to give the most efficient performance possible for a diffuser of this type.

One type of diffuser that is particularly advantageous is a so-called channel diffuser in which a series of vanes, extending between flangelike faces, form a series of tangentially directed diffuser passages. This type of diffuser gives good performance but it fails to provide sufficient divergence for the very high pressure increases desired in an advanced gas turbine engine. In addition, it is very expensive to manufacture and requires time-consuming manufacturing techniques. The reason for this is that each blade must be secured at its ends to both walls of the diffuser by welding.

The above ends are solved in accordance with the present invention by a compressor diffuser having a first annular element that has a substantially smooth face defined by an inner and outer diameter. The face is defined by straight-lined elements extending radially from the inner to the outer diameter. A second annular element abuts the face on the first element and has a plurality of tangentially directed channels open to the face to form a series of diffuser passages. The channels have an increasing cross-sectional flow area defined by an increasing channel height and width so that all of the divergence in the diffuser passages takes place in the channels formed in the second element.

The above and other related features of the present invention will be apparent from a reading of the following description of the disclosure shown in the accompanying drawing and the novelty thereof pointed out in the appended claims.

In the drawings:

FIG. 1 is a longitudinal, simplified section view of a gas turbine engine which has a compressor diffuser embodying the present invention;

FIG. 2 is an enlarged fragmentary cross-sectional view of the diffuser of FIG. 1, taken on line 2--2 of FIG. 1; and

FIG. 3 is a fragmentary cross-sectional view of the diffuser of FIG. 1, taken on line 3--3 of FIG. 2.

Referring to FIG. 1 there is shown a gas turbine engine comprising an output gearbox 10 which supports an annular inlet housing 12. Inlet housing 12 forms a bellmouth 14 to provide an annular inlet for ambient air into a compressor 16. Compressor 16 comprises an axially bladed hub 18, stator vanes 20 and a centrifugally bladed impeller 22. Hub 18 and impeller 22 are mounted on a central shaft 24 journaled for rotation at its upstream end by bearing assembly 26. The compressor 16 pressurizes and accelerates air for discharge radially outward through a compressor diffuser, generally indicated at 28, whose construction will be described in detail below. Air leaves the diffuser 28 with a substantially tangential component. Vanes 29, secured between inner and outer annular duct walls 31, 33, turn air to an axial direction for discharge into a chamber 30. Chamber 30 is formed by an outer housing 32 which mounts duct wall 33 and an inner cast strut assembly 34. A perforated combustor 36 in chamber 30 receives metered fuel from nozzles 38 for mixture with air passing inward through the perforations. The mixture is ignited by a suitable device and the resultant hot gas stream is turned by a turbine inlet duct 40 for discharge from a turbine inlet nozzle 42. The hot gas stream then passes across a bladed turbine rotor 44 also secured to shaft 24. A bearing assembly 46, supported by strut assembly 34, journals shaft 24 adjacent turbine rotor 44. From there the hot gas stream passes across a bladed power turbine rotor 48 which drives a gear set in the output box through a power turbine shaft 50.

The diffuser 28 forms an extremely important component of the engine. In accordance with the present invention it is constructed in such a way that economical mass production is possible without sacrificing excellent performance. The compressor diffuser 28 comprises a first annular element 52 secured to the annular inlet housing 12 through an integral structural cone 54, as shown in FIG. 1. The element 52 has an integral outer flange 56 having a shoulder 58 which receives the forward end 60 of housing 32. Housing 32 is secured to flange section 56 by a series of screws 62. Duct wall 33 is secured to housing 32 so that it is removed with housing 32.

Referring to FIG. 3, annular element 52 has a smooth aft-facing surface 64 defined by an inner diameter D.sub.1 and an outer diameter D.sub.2. The surface 64 is defined by straight-lined elements extending radially between the inner and outer diameters. Preferably, the surface 64 lies in a single plane at right angles to the axis of rotation of the compressor. A second annular element 66 abuts the surface 64 and has an integral structural cone 68 forming a structural component of the engine and an integral outer flange element 70 with a lip 72 defining an annular flow path between the housing 32 and the lip for passage of air to chamber 30 (see FIG. 1). The element 66 has a section corresponding to surface 64 which has an inner diameter d.sub.1 and outer diameter d.sub.2 generally corresponding to those on surface 64. Inner diameters D.sub.1 and d.sub.1 are spaced from the periphery of impeller 22 to form a vaneless annular inlet 69. This inlet may have an area controlled configuration, as disclosed in copending patent application entitled "Compressor Diffuser Inlet," Ser. No. 420,203, filed Nov. 29, 1973, T. Exley and C. Kuintzle inventors of common assignment with the present application.

As shown particularly in FIG. 2, element 66 has a series of channels 74 extending tangentially from the inner diameter d.sub.1. These channels 74 each have a throat 76 at their inlet end, a first diffusing section 78 and a second diffusing section 80. The throat sections 76 are formed by a section of constant channel height and width. The first diffusing section 78 is formed by a channel having an expanding width and depth. The channel diffusing section 80 is formed by an expanding channel depth and width which are greater than that for the intermediate section 78. As is apparent from FIG. 2, section 80 has a channel width C.sub.w which increases toward the downstream end of the passage. As is apparent from FIG. 3, the channel depth C.sub.d also increases in the downstream direction.

The result of forming channels 74 is a series of wedgelike sections 82 in between the channels 74 and having knife edge inlets 84. To permit securing of element 66 to element 52 a series of threaded holes 86 are provided in the wedge-shaped sections 82. These are aligned with suitable holes in the element 52 to permit the elements to be releasably secured by bolt assemblies 88. Holes 87, passing through wedges and the corresponding section of annular housing 52, provide access from one side of the diffuser to the other. Threaded holes 89 enable additional bolt assemblies 91 to hold the diffuser section together at that point and provide means to attach other elements, such as a bleed air conduit.

Element 66 may also be provided with a series of pockets 90 formed in the downstream section of wedge elements 82 and opening away from the surface 64, as shown in FIG. 1. These pockets enable the weight of the element 66 to be substantially reduced without decreasing its strength.

The diffuser 28 is easily manufactured using mass production techniques. Element 66 may be formed from a solid piece of material or cast in rough form. The channels 74 may be formed to very precise tolerances using standard milling techniques or electrochemical discharge. Alternatively, the element 66 may be cast from sintered material to produce the finished dimensions without further machinery, except for the sharpening of leading edges 84 on the wedges 82.

Once the passages are formed the forwardly facing surfaces of the wedge-shaped elements correspond to the plane of surface 64 and a tight fit is permitted between the two elements. When the diffuser is assembled by securing sections 52 and 66 together it is incorporated as part of the engine structure. Element 52, in addition to forming one portion of the diffuser, conveniently forms a portion of the exterior of the engine housing. The flange 70 in cooperation with the housing 32 conveniently forms a passage for flow of air from the diffuser to the combustor chamber 30. A diffuser of this type in operation is highly efficient since the passageway geometry can be controlled to a high degree of precision. At the same time the diffuser can be made using standard mass production techniques, thereby significantly decreasing the cost of an engine.

It should be noted that the degree of divergence for the above diffuser is significantly greater than that for a prior art channel diffuser. The reason is that the channels increase both in width and depth while the conventional diffuser channel increases in width only. Thus, a new dimension is available for providing increased divergence.

While a preferred embodiment of the present invention has been described, it should be apparent to those skilled in the art that it may be practiced in other forms without departing from its spirit and scope.

Claims

Having thus described the invention what is claimed as novel and desired to be secured by letters Patent of the United States is:

1. A compressor diffuser for use with a gas turbine engine having a generally annular housing comprising:

a first annular element having a substantially smooth face defined by an inner and outer diameter, said face being defined by straight-lined elements extending radially from said inner to said outer diameter, said first annular element forming a portion of said housing;

a second annular element having an inner and outer diameter substantially equal to the inner and outer diameter of the face on said first element, said second annular element abutting the face of said first element, said second element having a plurality of tangentially directed channels extending from the inner to the outer diameter of said second element to form a series of diffuser passages, said passages comprising an inlet throat section having a constant height and width, a first diffusing section having a height and width which expand at a first rate and a second diffusing section having a height and width which expands at a second faster rate, said widths expanding in the downstream portion of the channel whereby said diffuser sections provide an increasing cross-sectional flow area defined by an increasing channel depth and increasing channel width and whereby all of the divergence in the diffuser passageways takes place in said second element.

2. Apparatus as in claim 1 wherein said first annular element is in the form of a flange and said smooth face is in a radial plane.

3. Apparatus as in claim 1 wherein said gas turbine engine comprises a combustor positioned downstream from said diffuser and an outer housing surrounding said combustor, said outer housing being removably secured to the periphery of said first annular element.

4. Apparatus as in claim 3 wherein the first element has a periphery extending radially outward beyond the periphery of said second annular elemennt, said annular outer housing being attached to the periphery of said first element thereby forming an annular flow path turning air discharged from said diffuser from a radial to an axial direction.

5. Apparatus as in claim 4 wherein said second element has an aft flange and a curved lip positioned inward from said annular outer housing thereby defining, in part, said annular flow turning passage.

6. Apparatus as in claim 1 wherein said second annular element is a unitary piece of material having said passages formed in one face as a series of tangentially directed channels separated by generally wedge-shaped segments forming, in combination with the face on said first element, passages having a generally rectangular cross section.

7. Apparatus as in claim 6 further comprising means for releasably holding said first and second annular elements against one another.

8. Apparatus as in claim 7 wherein said releasable holding means comprises a plurality of bolts extending through one and threaded into the other of said elements.

9. Apparatus as in claim 6 wherein said second annular element is cast and has a plurality of pockets formed in said wedge-shaped portions, said pockets being opened to the face of said second element that is opposite the face in contact with the annular face on said first element.