One-piece compressor and turbine containment system

A compressor shroud for containing fragments of a compressor impeller and a turbine wheel within a gas turbine engine. The compressor shroud includes a compressor containment section, a turbine containment section, and a containment continuity section. The containment continuity section connects the compressor containment section and the turbine containment section to form a one-piece part.

BACKGROUND

The present invention relates to gas turbine engines. In particular, the invention relates to containment systems for gas turbine engines.

Gas turbine engines employ two relatively large components that rotate at very high speeds. These are a compressor impeller and a turbine wheel. The compressor impeller compresses incoming air which is directed to a combustion chamber, mixed with fuel and ignited. The turbine wheel is propelled by rapidly expanding gases resulting from the combustion of the fuel and the compressed incoming air. The compressor impeller is linked to, and powered by, the turbine wheel. Mechanical failure of either of these two components can result in considerable damage to the gas turbine engine. In some cases, pieces of the failed component may contain enough kinetic energy to penetrate a gas turbine engine housing and cause considerable damage outside the gas turbine engine. Therefore, it is frequently a requirement that the compressor impeller and the turbine wheel each have a containment device or system to prevent such flying fragments from escaping the engine.

Typically, a compressor impeller or turbine wheel containment system is a metal band or a series of metal bands surrounding either the compressor impeller section or the turbine wheel section of the engine. Such containment systems add weight, which reduces efficiency for gas turbine engines in transportation applications in general and is particularly problematic for applications aboard aircraft.

SUMMARY

The present invention includes a compressor shroud for containing fragments of a compressor impeller and a turbine wheel within a gas turbine engine. The compressor shroud includes a compressor containment section, a turbine containment section, and a containment continuity section. The containment continuity section connects the compressor containment section and the turbine containment section to form a one-piece part.

DETAILED DESCRIPTION

Conventional containment systems in gas turbine engines for a compressor impeller and a turbine wheel are separate, additional components adding weight and complexity. In addition, in conventional gas turbine engines, portions of engine components, such as a forward inlet bell mouth of a bearing capsule or a combustor assembly, are positioned radially outward from the compressor impeller or the turbine wheel, forcing compromises in manufacturing methods and material choices for these key components to enable them to not only perform their respective primary functions, but to contain flying fragments as well. Finally, conventional gas turbine engines have a flange connection between a compressor shroud and a combustor housing that is positioned radially outward from the compressor impeller or the turbine wheel. Such a flange connection is the weakest link in a conventional containment system.

The present invention solves these problems by extending the compressor shroud such that it is axially around both the compressor impeller and the turbine wheel. The extended compressor shroud is thickened as necessary to insure containment of flying fragments. The traditional separate containment systems for the compressor impeller and the turbine wheel are eliminated, reducing weight and complexity. With the compressor shroud providing containment, the forward inlet bell mouth and the combustor assembly no longer need to provide containment. This permits the use of manufacturing methods and materials better suited to their primary functions. Finally, the extended, one-piece compressor shroud has no flange connection positioned radially outward from the compressor impeller and the turbine wheel, improving reliability by removing the weakest link in a containment system.

Bearing capsule12attaches to compressor impeller36and to turbine wheel38of rotor assembly14along centerline axis CL, connecting compressor impeller36to turbine wheel38. Compressor shroud18axially surrounds compressor impeller36and turbine wheel38of rotor assembly14with compressor containment section18aaxially surrounding compressor impeller36, turbine containment section18baxially surrounding turbine wheel38, and containment continuity section18cbetween compressor containment section18aand turbine section18b. A first flanged end of compressor shroud18coextensive with an end of compressor impeller36farthest from turbine wheel38, attaches to bearing capsule12at forward inlet flange28. Forward inlet flange28is adjacent to bell mouth26, which contains forward inlet24. A second flanged end of compressor shroud18coextensive with an end of turbine wheel38farthest from compressor impeller36, attaches to combustor assembly16at combustor flange34. Combustor flange34is adjacent to combustor housing30, which contains combustion chamber32. Compressor shroud18also includes bleed slots18din compressor containment section18a. Bleed slots18dprovide compressed air for other aircraft systems and help regulate pressure around compressor impeller36to prevent engine performance problems, such as engine surge or blow-out. In the present invention, bleed slots18dare angled through compressor shroud18at an angle away from a radial orientation with respect to centerline axis CL, such that there is no direct radial path from compressor impeller36through bleed slots18d. Diffuser20is attached to compressor shroud by bolts22passing through bolt holes18e.

In operation, air enters forward inlet24of bearing capsule12at bell mouth26and is compressed by the centrifugal action of compressor impeller36. The compressed air is directed by compressor shroud18, through diffuser20, and into combustor housing30where it mixes with fuel and is ignited to produce a flame in combustor chamber32. Diffuser20comprises a series of impediments to air flow, such as angled vanes, to slow the compressed air, and increase its pressure, thereby preventing the compressed air from blowing out the flame in combustion chamber32. High temperature gases produced by the flame expand rapidly and propel turbine wheel38. Turbine wheel38, through its attachment to bearing capsule12, drives compressor impeller36and any additional systems attached to bearing capsule12. Compressor shroud18is an essential element of gas turbine10, directing compressed air from forward inlet24, through diffuser20, to combustion housing30.

In the present invention, compressor shroud18also serves a second essential function by providing containment of flying fragments for both compressor impeller36and turbine wheel38by extending axially around both components, as described above and illustrated in the FIGURE. In order to accomplish this second function, compressor shroud18is thicker than compressor shrouds that do not provide containment and is made of materials not normally used for compressor shrouds. Compressor shroud18is not of uniform thickness but is thicker in some areas to provide sufficient containment. The thickness of containment shroud18varies with proximity to a rotary component and expected incident angle of impact for flying fragments. For example, compressor containment section18ais thicker to provide the necessary containment for compressor impeller36, turbine containment section18bis thicker to provide the necessary containment for turbine wheel38, but need not be as thick as compressor containment section18a. Containment continuity section18cis thinnest of all because it is much more angled to a likely impact from a flying fragment compared to compressor continuity section18aor turbine containment section18b. Containment continuity section18chas bolt holes18eto accommodate bolts22for attaching diffuser20to containment shroud18. Also, as mentioned above, bleed slots18dare angled through compressor shroud18such that there is no direct radial path from compressor impeller36through bleed slots18d. This prevents flying fragments from compressor impeller36from passing unimpeded through compressor shroud18via bleed slots18d.

Containment shroud18is made of a material with mechanical properties desirable for containment, such as high strength and stability at high temperatures to provide resistance to piercing, as well as high elongation properties to provide high hoop tension. A suitable material is a nickel super alloy, for example, Inconel® 625. Containment shroud18is manufactured by a method that further enhances the desired mechanical properties, such as forging. Other manufacturing methods, such as casting, do not achieve the necessary strength for a given material thickness, requiring more material and greater weight to perform the same containment function. However, casting is more suitable than forging in creating more intricate and complex parts, such as bearing capsule12with bell mouth26. The complex shape of bell mouth26is critical for aerodynamics. The present invention, with the first flanged end of compressor shroud18coextensive with an end of compressor impeller36farthest from turbine wheel38, removes any containment requirement from bearing capsule12, permitting bearing capsule12to be cast without requiring extra material in bearing capsule12to provide a containment function.

As shown in the FIGURE, combustor assembly16also does not need to perform any containment function in the present invention. This permits a more efficient design, with no need to accommodate or work around a separate containment band within combustor assembly16. A combustor flange for a combustor assembly in a conventional gas turbine engine is located approximately between the gas turbine engine's compressor impeller and turbine wheel, thus requiring at least a portion of the combustor assembly to provide containment for the turbine wheel. In the present invention, combustor flange34is not positioned axially around turbine wheel38, so there is no need for combustor assembly16to provide containment.

As noted above, conventional gas turbine engines have a combustor flange between a compressor shroud and a combustor housing that is positioned radially outward from either the compressor impeller or the turbine wheel. This flange typically represents the weakest link in a conventional containment system. The present invention, with single piece compressor shroud18providing containment for both compressor impeller36and turbine wheel38as described above, has no flanges in the region radially outward from compressor impeller36or turbine wheel38. This feature eliminates the weakest link in a containment system.

Finally, replacing three components, a conventional compressor shroud, a conventional compressor impeller containment system and a conventional turbine wheel containment system with one component, compressor shroud18, provides significant benefits in simplifying and reducing costs associated with manufacturing, assembling, and controlling inventory. Attaching compressor shroud18is no more difficult than attaching any conventional compressor shroud, but the operations necessary to manufacture, inventory, deliver and attach the conventional compressor impeller containment system and the conventional turbine wheel containment system are completely eliminated. In addition, moving from three components to one also provides an opportunity for weight savings, which is important in transportation applications and critically important in aircraft applications.