The present invention relates to turbomachinery and vanes for guiding air flow through a turbomachine. More particularly, this invention relates to a fan outlet guide vane frame comprising sectors of outlet guide vanes formed of different materials, in which some of the sectors are load-bearing and others are not.
High-bypass turbofan engines are widely used for high performance aircraft that operate at subsonic speeds. As schematically represented in FIG. 1, a high-bypass turbofan engine 10 includes a large fan 12 placed at the front of the engine 10 to produce greater thrust and reduce specific fuel consumption. The fan 12 serves to compress incoming air 14, a portion of which flows into a core engine (gas turbine) 16 that includes a compressor section 18 containing low and high pressure compressor stages 18A and 18B to further compress the air, a combustion chamber 20 where fuel is mixed with the compressed air and combusted, and a turbine section 22 where a high pressure turbine 22A extracts energy from the combustion gases to drive the high pressure stages 18A of the compressor section 18 and a low pressure turbine 22B extracts energy from the combustion gases to drive the fan 12 and the low pressure stages 18B of the compressor section 18. A larger portion of the air that enters the fan 12 is bypassed to the rear of the engine 10 to generate additional engine thrust. The bypassed air passes through an annular-shaped bypass duct 24 that contains one or more rows of stator vanes, also called outlet guide vanes 28 (OGVs), located immediately aft of the fan 12 and its fan blades 26. The fan blades 26 are circumscribed by a fan casing 32, which in turn is surrounded by the fan cowling or nacelle 34 that defines the inlet duct 36 to the turbofan engine 10 as well as a fan nozzle 38 for the bypassed air exiting the bypass duct 24.
The outlet guide vanes 28 form part of a vane frame 40 that further includes inner and outer shrouds 42 and 44 at the radially inward and outward extents, respectively, of the guide vanes 28. A common construction is to form the vane frame 40 of segments, each comprising one or more vanes 28 connecting a pair of inner and outer shroud segments. The outer shroud 44 (formed by the assembly of the outer shroud segments) is secured to the fan casing 32, while the inner shroud 42 (formed by the assembly of the inner shroud segments) is secured to the core engine 16, and more particularly to an inner frame (not shown) of the core engine 16. The fan nacelle 34 is shown in FIG. 1 as attached to and supported by the core engine 16 through the outlet guide vanes 28. The guide vanes 28 have cambered airfoil shapes to modify the air flow through the bypass duct 24 to promote deswirling of the fan air, thus improving efficiency and reducing engine noise.
Because of its dual functions, the vane frame 40 is an important structural component whose design considerations include aerodynamic criteria as well as the ability to provide sufficient structural support and stiffness to the fan nacelle 34 for maintaining the shape of the inlet duct 36 and adequately transitioning static and dynamic loads to the engine core 16. For these reasons, it is important to select appropriate constructions, materials and assembly methods when manufacturing the vane frame 40 and its individual components, including the guide vanes 28 and inner and outer shrouds 42 and 44 and their connections to the fan casing 32 and core engine 16. Various materials and configurations for outlet guide vanes have been considered. Metallic materials, and particularly aluminum alloys, have been widely used. Composite materials have also been considered, as they offer the advantage of significant weight reduction. However, in order to be reliably capable of supporting the fan nacelle and transitioning fan nacelle loads, outlet guide vanes formed of composite materials have generally required complex attachment geometries and hardware, which increases weight and manufacturing and material costs.