Rotary kinetic fluid motors or pumps – Including destructible – fusible – or deformable non-reusable...
Reexamination Certificate
1999-09-07
2001-03-27
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
Including destructible, fusible, or deformable non-reusable...
C415S173400, C415S215100
Reexamination Certificate
active
06206631
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to turbomachinery and blade containment structures for minimizing structural damage due to blade release. More particularly, this invention relates to a dual-wall containment casing for turbomachinery, such as a high bypass turbofan engine, in which the casing has a multi-component construction of different materials and is configured to benefit from the different mechanical and physical properties of the materials.
BACKGROUND OF THE INVENTION
High bypass turbofan engines are widely used for high performance aircraft that operate at subsonic speeds. These engines have a large fan placed at the front of the engine to produce greater thrust and reduce specific fuel consumption. The fan serves to compress incoming air, a portion of which is then delivered to the combustion chamber, with a larger portion being bypassed to the rear of the engine to generate additional engine thrust. The fan is circumscribed by a fan casing that must be capable of containing and minimizing damage to the engine from the remote event of a fan blade that is released from its hub during engine operation. For this reason, fan casings are equipped with specialized blade containment structures that serve to minimize structural damage to the engine as well as the aircraft to which the engine is mounted.
Various materials and configurations for blade containment structures have been proposed. Steel is well suited for blade containment on the basis of its mechanical properties, and particularly its toughness (strain to failure). However, a significant drawback to the use of steel in aerospace applications is its density. Consequently, thin steel containment structures coupled with a wrap formed of KEVLAR® or another fiber-reinforced polymer material have been developed. While reducing weight, these containment structures are characterized by significantly higher manufacturing costs. Containment structures formed of relatively lightweight metals such as aluminum alloys have also been used, though they do not provide the level of high toughness and other desirable mechanical properties possible with steel.
An additional consideration for blade containment structures is the natural frequency of the casing and the avoidance of blade/case interaction. The frequency of steel containment structures has typically been increased above blade/case interaction frequencies by the inclusion of rings that are integral with or bolted to the structure. Frequency-altering measures such as integral or bolt-on rings have also been required with aluminum containment structures. For steel containment structures coupled with fiber-reinforced polymer wraps, a honeycomb structure between the steel component and the wrap has been used to increase the natural frequency of the casing assembly. In addition to additional material, and manufacturing and assembly costs, each of the above modifications for addressing blade/case interaction incurs the penalty of unwanted weight, space and cost.
From the above, it can be seen that improvements in blade containment through material selection based on mechanical properties and the structural requirements for avoiding blade/case interaction have combined to increase the weight and cost of manufacturing high bypass turbofan engines. It would be desirable if a blade containment structure were available that exhibited the blade containment capabilities of steel casings but without the weight penalty associated with steel, while also maintaining fan casing natural frequencies at acceptable margins to avoid blade/case interactions.
BRIEF SUMMARY OF THE INVENTION
According to the present invention, there is provided a blade containment structure for a fan casing of turbomachinery, such as a high bypass turbofan engine. The blade containment structure of this invention includes a first casing member having a wall that defines an inner containment shell immediately surrounding the blades of the turbomachine, and a second casing member assembled to the first casing member. The second casing member has a wall that defines an outer containment shell surrounding the inner containment shell of the first casing member, such that a cavity is defined by and between the inner and outer containment shells. According to the invention, the first casing member is formed from a relatively tough material such as a stainless steel or a nickel-base alloy, while the second casing member is formed from a material that is less dense than the material of the first casing member. The material of the second casing member may also have lower toughness as compared to the material of the first casing member.
The overlapping portions of the first and second casing members provide for a multi-component containment structure whose ability to contain a released blade benefits from the toughness of the first casing member immediately adjacent the blades. Simultaneously, the containment structure benefits from the relatively low weight of the second casing member, which preferably forms the balance of the containment structure such that the overall weight of the fan casing is significantly lower than that possible if the entire containment structure was formed of the material of the first casing member. The overlapping portions of the first and second casing members also provide a load path if the first casing member is torn on blade impact, and the cavity defined by the overlapping portions can be sized and configured to accommodate a variety of devices that provide positive damping between the casing members to react any case vibrational interaction with the blades.
Other objects and advantages of this invention will be better appreciated from the following detailed description.
REFERENCES:
patent: 4534698 (1985-08-01), Tomich
patent: 4648795 (1987-03-01), Lardellier
patent: 5431532 (1995-07-01), Humke et al.
patent: 5437538 (1995-08-01), Mitchell
patent: 5486086 (1996-01-01), Bellia et al.
patent: 1466385 (1977-03-01), None
General Electric Company
Herkamp Nathan D.
Hess Andrew C.
Look Edward K.
McDowell Liam
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