Rotary kinetic fluid motors or pumps – Including destructible – fusible – or deformable non-reusable...
Reexamination Certificate
1998-12-07
2001-05-01
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
Including destructible, fusible, or deformable non-reusable...
C415S174400, C415S224500
Reexamination Certificate
active
06224321
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a containment system for containing a burst impeller or impeller fragments and, in particular, an impeller containment system that utilizes a cooperating snagger and catcher to contain the tangential movement of a burst impeller or impeller fragments.
2. Description of the Prior Art
Aircraft engines and auxiliary power units are known to include turbines and compressors which rotate about a central shaft at high rotational speeds. Although modern gas turbine engines and auxiliary power units can perform for thousands of hours without any significant malfunction, circumstances have arisen where turbine blades or impeller blades can burst from their rotational hub. In general, when such a burst occurs, it is most desirable to contain such hub fragments of the burst disk within the shortest possible radius. In this way, the material cross-section required to provide the necessary shear and hoop strength to contain the burst can be minimized to reduce weight, while still maintaining a sufficient factor of safety for protection of the engine and aircraft systems and structure.
It is also desirable to contain the burst within the shortest axial distance as can be obtained, so that the range of trajectories of burst fragments resulting from a burst will be minimal. In practice within the prior art, impeller hub fragments have been contained by using impeller shrouds, diffusers, and the outer engine cases as the primary containment structures. However, the conventional prior art impeller shrouds and diffusers have sometimes failed to contain the hub burst over sufficiently small axial and radial distances. In the conventional prior art, these containment structures have tended to be remote from the respective origin of burst. Consequently, in order to span the anticipated range of trajectories of burst fragments, these containment structures have been axially long and radially thick such that their cross-sections have been massive relative to adjacent normal engine structure. Tests have shown that these structures can be inefficient with respect to their weight.
An undesirable feature of these structures is that the burst fragments are generally unrestrained until they have reached the outer structure of the engine, by which time the fragments can be unfavourably oriented for efficient containment having been deflected from the original plane of rotation, both by intermediate structure and by the mode of break-up of the disk since each failure event can be different.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a containment structure which contains burst hub fragments within the shortest possible radius and the shortest possible axial distance from the point of burst.
It is another object of the present invention to provide an impeller containment system which protects engine components from tri-hub burst, as will be explained, but which is designed to minimize added material and thus added weight to an engine.
It is a further object of the present invention to provide an impeller containment system in which the impeller itself forms part of the containment system, so as to minimize the travel of impeller fragments during an impeller burst.
It is a feature of the present invention to provide a containment system for containing fragments of a rotating impeller, resulting from a burst impeller within a housing, where the impeller comprises an annular impeller hub mounting impeller blades on the hub, the hub including an annular recessed portion; and containment means surrounding said impeller hub, said containment means including a catcher for catching a burst portion of said hub by engaging the annular recessed portion of said hub. More specifically, the containment means also includes a curved shroud surrounding the impeller blades.
It is a feature of the invention, from a broad aspect, to provide a containment system in which a portion of the impeller hub is formed with a concave recess to form a “snagger”, and a portion of the shroud back plate downstream of the impeller hub is formed with a convex flange to form a “catcher”. During an impeller burst, the impeller snagger is designed to engage the shroud back plate catcher. Because the center of gravity of the impeller is axially offset from the center of gravity of the blade tip shroud, a burst impeller fragment will tend to slide rearwards and tend to push the shroud forward. Since the groove on the impeller hub portion fits complementarily with the flange on the rear of the shroud, the impeller will be snagged by the flanged portion of the back plate shroud and be restrained from traveling any farther radially outward or longitudinally rearward. The hub is also constrained from moving more than a few inches from the point of burst.
It is another feature of the present invention, from a broad aspect, to provide a diffuser which is arranged to serve as a complementary containment structure for containing burst impeller fragments. The diffuser of the present invention is a circumferential ring arranged radially outward of the tip of the impeller blades. The diffuser is sized so that it will contain structure for any impeller fragments traveling in the tangentially outward direction between the curved shroud and the shroud back plate. The diffuser is also designed with a groove which will trap outward expansion of the curved shroud resulting from the high energy shock of the hub burst.
The invention can apply to any high speed rotating unit where safety and weight efficiencies are considerations, such as pumps, compressors, fans, etc.
REFERENCES:
patent: 3613360 (1971-10-01), Howes
patent: 3652176 (1972-03-01), Walsh
patent: 4264271 (1981-04-01), Libertini
patent: 4687412 (1987-08-01), Chamberlain
patent: 5427498 (1995-06-01), Lehe et al.
patent: 5601406 (1997-02-01), Chan et al.
patent: 5618162 (1997-04-01), Chan et al.
patent: 676737 (1991-02-01), None
patent: 0 834 646 (1998-04-01), None
PCT International Search Report, Mar. 13, 2000, European Patent Office.
Ebden Clive
Gomuc Reha
Look Edward K.
McDowell Liam
Pratt & Whitney Canada Inc.
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