The present invention generally relates to systems for containing a burst impeller or impeller fragments and, more particularly, to containment systems that include a vaneless diffuser.
A prior art compressor 30, as depicted in
U.S. Pat. No. 6,695,574 discloses an energy absorber and deflection device for deflecting engine debris fragments from a core of a gas turbine engine. The device includes a deflection plate radially spaced from and adapted to cover any rotating component of the engine. The disclosed device may be used to contain fan blade fragments, rotor fragments, broken shaft fragments, compressor fragments, turbine blade fragments or turbine rotor fragments. Unfortunately, the deflection plate adds weight to and increases the envelope of the engine. Although the described device may be used to contain engine debris, it is not suitable for some applications due to envelope and weight restrictions.
U.S. Pat. No. 6,224,321 discloses an impeller containment system. The described system utilizes a catcher extending from a shroud plate adjacent to the impeller, which engages with a snubber formed as a unitary part of the impeller. The catcher and snubber cooperate to restrain a burst impeller or impeller fragments to their shortest radial distance from their point of burst. The described system also includes a shroud, which circumferentially surrounds the impeller and a diffuser, which circumferentially surrounds the radial tip portions of the impeller. The back plate of the described containment system has a catcher groove and flange and the impeller has a snubber groove and flange. These grooves and flanges increase the complexity of the compressor components. The described system adds further complexity by including a bayonet flange on the impeller shroud that is designed to interact with a recessed grooved portion of the diffuser.
Other fragment containment methods have included increasing the strength of the shroud by increasing the thickness of the housing walls. Unfortunately, increasing wall thickness increases system weight.
For some compressors, the inclusion of vaned diffusers can provide sufficient fragment containment. Unfortunately, vaned diffusers are not suitable for all compressor designs.
As can be seen, there is a need for improved containment systems. Additionally, containment systems are needed that do not adversely affect the weight and envelope of the engine/machine. Further, simple containment systems are needed that do not require complex component designs. Moreover, containment systems are needed for compressor designs that do not include vaned diffusers.
In one aspect of the present invention, a system for an impeller comprises a housing surrounding the impeller; a diffuser passage defined by the housing; and at least one passage obstructer having an obstructing portion, the obstructing portion extending through the diffuser passage.
In another aspect of the present invention, an apparatus for a compressor having a vaneless diffuser comprises a fastener portion; and an obstructing portion integral to the fastener portion, the obstructing portion extending axially through the vaneless diffuser.
In a further aspect of the present invention, a method of containing a burst impeller fragment comprises the steps of obstructing a path of the burst impeller fragment with at least one passage obstructer; and adsorbing at least a portion of the energy of the burst impeller fragment.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.
The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.
Broadly, the present invention provides containment systems and methods for containing burst impellers. Embodiments of the present invention may find beneficial use in many industries including aerospace, automotive and electricity generation. Embodiments of the present invention may be beneficial in applications including manufacturing and repair of aerospace components. Embodiments of the present invention may be useful in all radial debris containment application, such as but not limited to, burst impeller containment for aircraft engines.
In one embodiment, the present invention can incorporate modified fasteners (passage obstructers) at some of their existing locations to enhance the in-situ containment capacity during a tri-hub burst test. The passage obstructers can replace the existing housing fasteners used in the first stage vacuum generator compressor inlet cover/middle housing to tie in with the second stage vacuum generator compressor back housing. The passage obstructers of the present invention can be positioned such that they extend axially through the diffuser of the compressor to obstruct the path of the burst impeller fragments. Unlike the prior art that includes a deflection plate radially spaced from the compressor, the present invention does not adversely affect the weight or the envelope of the machine. Unlike the prior art that includes complex snubbers and catchers, the present invention can include simple modified fasteners that comprise extended studs. Unlike the prior art designs that require vaned diffusers for fragment containment, the present invention can be used with compressor designs having vaneless diffusers.
A containment system 40 installed in a compressor 60, according to an embodiment of the present invention is depicted in
The passage obstructer 41, as depicted in
The fastener portion 42, as depicted in
The dimensions of the fastener shaft 45 may vary with application. The length of the fastener shaft 45 (fastener shaft length 51) may depend of the thickness of the housing 63 and on the number of housing members through which the fastener shaft 45 extends. For example, for some two-stage compressor applications the fastener shaft length 51 may be between about 1.0 and about 3.0 inches. For some single-stage compressor applications the fastener shaft length 51 may be between about 0.50 and about 1.00 inches. The diameter of the fastener shaft 45 (fastener shaft diameter 50) may vary with application and may depend on the closing force required for the housings and operating conditions. For example, for some two-stage compressor applications, the fastener shaft diameter 50 may be between about 0.060 and about 0.250 inches.
The obstructing portion 43, as depicted in
The obstructing portion 43 may be designed such that the obstructing portion 43 may be bent by the impact of an impeller fragment. The obstructing portion 43 may obstruct the path of the fragment, reduce the velocity of the fragment or stop the outward movement of the fragment. The dimensions of the obstructing portion 43 may vary with application. The length of the obstructing portion 43 (obstructing portion length 52) may depend on the width of the diffuser passage 67 (diffuser passage width 53) and the depth of the recess 68 (recess depth). For some applications, the obstructing portion length 52 may be at least about equal to the sum of the width of the diffuser passage 67 plus the depth of the recess 68, as depicted in
The depth of the recess 68 may be about equal to or greater than the length of the penetrating portion of the elongated member 46. The depth of the recess 68 may depend on the thickness of the back housing 66 and may be designed such that the recess 68 does not adversely affect the structural integrity of the back housing 66. For example, the depth of the recess 68 may be between about 0.050 and about 0.10 inches when the thickness of the back housing 66 is about 0.20 inches. The depth of the recess 68 may be deep enough to retain at least some of the obstructing portion 42. In other words, the recess may be deep enough to prevent the second end 48 of the obstructing portion 43 from easily sliding along the surface of the back housing 66 to prevent plastic bending deformation. For some aircraft applications, the depth of the recess 68 may be at least about 0.025 inches. The recess 68 may be formed by conventional machining techniques or casting methods.
The containment system 40 may comprise at least one passage obstructer 41. The number of passage obstructers 41 may vary with application and may depend on the dimensions of the impeller 61 and the requirements of the compressor 60. For some two-stage aircraft compressors, the number of passage obstructers 41 may be between about 1 and about 12. The containment system 40 may comprise a plurality of circumferentially spaced passage obstructers 41, as depicted in
The housing 63, as depicted in
The diffuser passage 67 may comprise a passage positioned between the impeller 61 and the scroll housing containment structure 69. The diffuser passage 67 may comprise a vaneless diffuser, as depicted. The vaneless diffuser may include an annular volume that circumferentially surrounds the impeller 61. The annular volume may be designed to receive the supply of compressed air from the impeller 61 and to reduce the velocity of the compressed air. For some embodiments, the diffuser passage 67 may comprise other diffuser types, such as a vaned diffuser.
A method 100 of containing a burst impeller fragment that is traveling along a path in a radially outward direction is depicted in
The step 110 of obstructing the path of the burst impeller fragment may comprise obstructing the path of the burst impeller fragment such that the direction of the burst impeller fragment is altered by contact with the passage obstructer 41. The step 110 of obstructing the path of the burst impeller fragment may comprise obstructing the path of the burst impeller fragment such that the radial movement of the burst impeller fragment is ceased by contact with the passage obstructer 41.
The step 120 of absorbing at least a portion of the energy of the burst impeller fragment may comprise absorbing at least a portion of the energy of the burst impeller fragment with the passage obstructer 41. The step 120 of absorbing at least a portion of the energy of the burst impeller fragment may comprise absorbing the energy of the burst impeller fragment such that the velocity of burst impeller fragment is reduced by contact with the passage obstructer 41. The step 120 of absorbing at least a portion of the energy of the burst impeller fragment may include bending an obstructing portion 43 of the passage obstructer 41 by impacting the obstructing portion 43 with the burst impeller fragment.
A containment system 40 according to an embodiment of the present invention was installed on a compressor 60. Nine passage obstructers 41 were used to replace existing fasteners in the compressor housing 63. Each passage obstructer 41 was positioned such that a portion of the passage obstructer 41 extended through the diffuser passage 67 of the compressor 60. The passage obstructers 41 were circumferentially spaced, as depicted in
A tri-hub test was performed. Generally, in practice, an impeller 61 will break from a single failure origin, often from a fault in the bore, where the stress is often maximum. The exact fracture mode is unpredictable and can result in impeller fragments of various sizes and shapes. Theoretically, the most dangerous and damaging failure configuration is a failure that produces three equal impeller fragments. For a tri-hub test, three evenly spaced slots are cut into the hub of the impeller 61 to weaken the hub to the point where it bursts at, or marginally above, the maximum operating speed of the compressor 60. The results of the tri-hub test are shown in
As can be appreciated by those skilled in the art, the present invention provides improved containment systems. Embodiments of the present invention can provide impeller containment systems that do not adversely affect the weight and envelope of the engine. Embodiments of the present invention can provide impeller containment systems for use with vaneless diffusers.
It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.
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