Patent Application
20130084174
Gas turbine engines (or combustion turbines) are built around a center body, holding a power core made up of a compressor, combustor and turbine, arranged in flow series with an upstream inlet and downstream exhaust. The compressor compresses air from the inlet, which is mixed with fuel in the combustor and ignited to generate hot combustion gas. The turbine extracts energy from the expanding combustion gas, and drives the compressor via a common shaft. Energy is delivered in the form of rotational energy in the shaft, reactive thrust from the exhaust, or both.
A fan section pulls air into the engine, and is surrounded by an outer fan casing which defines an air flow path. The outer casing must be structurally connected to the center body. This connection can be made with aerodynamic vanes that are called structural guide vanes because they provide the structural connection between the outer casing and the center body. These structural guide vanes can turn and straighten swirling air after it passes through the fan rotor.
Turbofan engines are commonly divided into high and low bypass configurations. High bypass turbofans generate thrust primarily from the fan, which drives airflow through a bypass duct oriented around the engine core. This design is common on commercial aircraft and military transports, where noise and fuel efficiency are primary concerns. Low bypass turbofans generate proportionally more thrust from the exhaust flow, providing greater specific thrust for use on supersonic fighters and other high-performance aircraft. Unducted (open rotor) turbofans and ducted turboprop configurations are also known, as are a variety of counter-rotating and aft-mounted designs.
Turbofan engine performance depends on precise control of the working fluid flow. Because engine noise is a factor, however, particularly for aviation applications, there are competing engineering challenges for both fan and compressor design.
A reinforced structural guide vane system includes an outer casing; a center body within the outer casing; a plurality of structural guide vanes extending between and connected to the center body and the outer casing; and a plurality of strut rods extending between and connected to the outer casing and to the center body.
Air is taken in through fan 12 as fan 12 spins. A portion of the inlet air is directed to compressor section 14 where it is compressed by a series of rotating blades and stationary vanes. The compressed air is mixed with fuel, and then ignited in combustor section 16. The combustion exhaust is directed to turbine section 18. Blades and vanes in turbine section 18 extract kinetic energy from the exhaust to turn inner (low spool) shaft 24A, which drives low pressure compressor 20 and turbofan 12, and outer shaft 24B which drives high pressure compressor 22.
The portion of inlet air that is taken in through fan 12 and not directed through compressor section 14 is bypass air. When fan 12 spins, it creates pressure and imparts swirl into the air. Guide vanes 28 act to slow down and straighten the air, increasing static pressure and creating thrust.
Structural guide vanes 28 are connected to center body 34 at inner ends 36 and to outer casing 32 at outer ends 38. This connection can be through bolts or any other connection means to secure them on inner ends 36 and outer ends 38. Structural guide vanes 28 are swept back so that they are connected at inner ends 36 to center body 34 at a location closer to fan 12 than the connection to outer casing 32 at outer ends 38. Strut rods 30 are connected to center body 34 at inner ends 40 and to outer casing 32 at outer ends 42. These connections can be by bolts or another method known in the art.
In
Structural guide vanes 28 are very thin, making them lightweight but susceptible to torsional winds and stresses from swirling fan air. Additionally, structural guide vanes 28 are susceptible to other catastrophic load conditions in an engine, such as the loss of a fan blade which may directly impact structural guide vanes 28 and/or may cause severe vibrations within the engine. By connecting outer ends 42 of strut rods 30 at locations close to outer ends 38 of guide vanes 28, strut rods 30 reinforce structural guide vanes 28, adding torsional stability and torsional rigidity for structural guide vanes 28. The insertion, placement and angles of strut rods 30 allows structural guide vanes 28 to withstand normal loading as well as many catastrophic loading conditions.
Additionally, the use of strut rods 30 allows for the placement of structural guide vanes 28 close to the fan to efficiently straighten air. Pressure pulsations arriving from rotation of upstream fan blades generate noise when they encounter structural guide vanes 28. The smaller the distance between fan blades and structural guide vanes 28, the louder the noise generated. This noise must be kept to a minimum, so sweeping structural guide vanes 28 reduces noise while allowing placement close to the fan. The sweep angle in structural guide vanes 28 combined with the placement and angle of strut rods 30 provide a wide base to distribute vertical loads and prevent bending loads in structural guide vanes 28 while allowing placement toward the front of the center body 34.
In these embodiments, rods 30 are connected in H-frame arrangements, forming a sort of “H” around center body 34. In
In summary, strut rods 30 are added to fan exit casing C, C′, or C″ to reinforce structural guide vanes 28, bringing additional torsional stability and torsional rigidity to vanes 28. Strut rods 30 connect at outer ends 42 to outer casing 32 at locations close to outer end 38 connections of structural guide vanes 28 to outer casing 32. This allows structural guide vanes 28 to stay thin and light weight while ensuring they are strong enough to endure engine loads, including normal loads from airflow from a fan or loads from catastrophic events such as a fan blade loss. Strut rods 30 are connected to center body 34 and to outer casing 32 at specific positions to reinforce structural guide vanes 28, allowing structural guide vanes 28 to be swept back, keeping the center body 34 connection near the fan while minimizing noise generated from a close connection.
While the placement of structural guide vanes and strut rods has been shown in three embodiments (A-frame and two variations of H-frames), strut rods can be placed in different positions and at different angles to reinforce and add torsional stability and torsional rigidty to the structural guide vanes. The only requirement is that they are not extending out radially from the center body to ensure that they can take torsional loads. While the invention has been shown with individual structural guide vanes, the structural guide vanes can be arranged in multipacks, with two or more vanes made integral to each other.
While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.
