Overlap interface for a gas turbine engine composite engine case

[0001] This invention was made with government support under Contract No.: N00019-02-C-3003. The government therefore has certain rights in this invention.

[0002] The present invention relates to an engine case for a gas turbine engine.

[0003] A gas turbine engine, such as a turbofan engine for an aircraft, includes a fan section, a compression section, a combustion section, and a turbine section. An axis of the engine is centrally disposed within the engine, and extends longitudinally through these sections. A primary flow path for working medium gases extends axially through the engine. A secondary flow path for working medium gases extends radially outward of the primary flow path.

[0004] The secondary flow path is typically defined by a bypass duct formed from a multiple of portions which are fitted together along a flange arrangement. Although effective for metallic duct structures, composite bypass ducts for military engines require other interface arrangements. The viability of turned-up axial flanges on composite components may be relatively low due to a lack of duct circumferential stiffness at mid-span. Additional difficulties may arise in mitered turned-up axial and circumferential flanges.

[0005] The composite engine case according to the present invention provides an axial interface for single-walled composite pressure vessels utilized in gas turbine engines. One configuration includes an alternating mix of full length and partial plies to provide the total thickness required at the axial interface. This configuration provides for strength through the thickness at the axial interface. Another configuration provides only full-length structural plies at the axial interface. Flyaway inserts co-cured into the lay-up along the inner mold line (IML) side provide the required thickness.

[0006] The composite engine case without the complications of a 3D or corner turned-up flange provides a less labor-intensive lay-up process; a simpler mold; less likelihood for voids due to tight/sudden bends; and more efficient use of ply orientation at the axial interface.

[0007] The present invention therefore provides an effective axial interface for multi-section composite engine cases with substantial circumferential stiffness at mid-span.

[0016] FIG. 1 schematically illustrates a gas turbine engine 10 which generally includes a fan section 12, a compressor section 14, a combustor section 16, a turbine section 18, an augmentor section 19, and a nozzle section 20. The compressor section 14, combustor section 16, and turbine section 18 are generally referred to as the core engine. An axis of the engine A is centrally disposed and extends longitudinally through these sections. Within and aft of the combustor 16, engine components are typically cooled due to intense temperatures of the combustion core gases.

[0017] An outer engine duct structure 22 and an inner cooling liner structure 24 define an annular secondary fan bypass flow path 26 around a primary exhaust flow (illustrated schematically by arrow E). It should be understood that various structure within the engine may be defined as the outer engine case 22 and the inner cooling liner structure 24 to define various cooling airflow paths such as the disclosed fan bypass flow path 26. The fan bypass flow path 26 guides a secondary flow or cooling airflow (illustrated schematically by arrows C, FIG. 2) between the outer engine case 22 and the inner cooling liner structure 24. Cooling airflow C and/or other secondary airflow that is different from the primary exhaust gas flow E is typically sourced from the fan section 12 and/or compressor section 14. The cooling airflow C is utilized for a multiple of purposes including, for example, pressurization and partial shielding of the nozzle section 20 from the intense heat of the exhaust gas flow F during particular operational profiles.

[0018] The fan bypass flow path 26 is generally defined by the outer engine case 22 having a first section 40A which may be an upper half and a second section 40B which may be a lower half (FIG. 2). The first section 40A engages the second section 40B along an axial interface 42 (illustrated as a lateral section in FIG. 3). It should be understood that although the first section 40A and the second section 40B are disclosed as a particular module of the engine and that other engine sections and pressure vessels may alternatively or additionally benefit from the axial interface 42.

[0019] Referring to FIG. 3, the axial interface 42 includes an alternating mix of full-length and partial-length plies to provide a desired total thickness required for strength at the axial interface 42. This configuration provides for strength through the thickness of the integration of partial-length plies at the axial interface 42. That is, the outer engine case 22 is thicker adjacent the axial interface 42 than at the remainder of the first section 40A and the second section 40B. The thickness may begin to increase in the respective first section 40A and second section 40B at approximately 30 degrees and 20 degree circumferential position defined on each side of the axial interface 42 (FIG. 4). Generally, the increased thickness at the axial interface is provided by non-structural build-up plies integrated or added to the structural plies (FIG. 5). Alternatively, the non-structural build-up plies may be eliminated such that only the lap-joint of structural plies remain.

[0020] The axial interface 42 defines a stepped interface 44 in lateral cross-section. The stepped interface 44 is defined by an extended portion 46 of the first section 40A which overlaps an extended portion 48 of the second section 40B. The full length continuous plies are located along ether side of the extended portions 46, 48 to provide an overlap which minimizes delamination and crack propagation at the axial interface 42.

[0021] The first section 40A of the stepped interface 44 defines first ledge 50A and the second section 40B defines a second ledge 50B. The extended portion 46 of the first section 40A rests upon the second ledge 50B of the second section 40B while the extended portion 48 of the second section 40B rests upon the first ledge 50A of the first section 40A.

[0022] A seal 52 may be located along the first ledge 50A to seal the first section 40A and the second section 40B about an outer perimeter thereof. Alternatively, a portion of the first section 40A above the extended portion 48 of the second section 40B may be removed along with the axial seal 52.

[0023] The extended portion 46 of the first section 40A overlaps the extended portion 48 of the second section 40B to define a lap joint which receives a multiple of fasteners 54. The multiple of fasteners 54 may be arranged in a stagger pattern (FIG. 6) which minimizes the number of fasteners required by providing additional outer engine case 22 material therebetween.

[0024] Referring to FIG. 7, another axial interface 42′ includes only full-length structural plies to define a portion of the stepped interface 44′ as described above. The axial interface 42′ includes flyaway inserts 56 co-cured into the lay-up along the inner mold line (IML) side to provide the required thickness. It should be understood that other lightweight inserts which provide the desired thickness may alternatively or additionally be provided.

[0025] It should be understood that relative positional terms such as “forward,” “aft,” “upper,” “lower,” “above,” “below,” and the like are with reference to the normal operational attitude of the vehicle and should not be considered otherwise limiting.

[0026] It should be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit from the instant invention.

[0027] Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present invention.

[0028] The foregoing description is exemplary rather than defined by the limitations within. Many modifications and variations of the present invention are possible in light of the above teachings. The disclosed embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.