Abstract:
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 extended between and connected to the outer casing and to the center body.

Description:
BACKGROUND 
       [0001]    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. 
         [0002]    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. 
         [0003]    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. 
         [0004]    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. 
       SUMMARY 
       [0005]    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. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a cross-sectional view of a gas turbine engine with strut rods according to the current invention. 
           [0007]      FIG. 2A  is a perspective view of structural members of a fan exit case with structural guide vanes and strut rods from a front side. 
           [0008]      FIG. 2B  is a view of  FIG. 2A  with the structural guide vanes removed. 
           [0009]      FIG. 3  is a perspective view of a back side of a second embodiment of a fan exit case with structural guide vanes and strut rods. 
           [0010]      FIG. 4  is a perspective view of a back side of a third embodiment of a fan exit case with structural guide vanes and strut rods. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]      FIG. 1  is a cross-sectional view of gas turbine engine  10 , which includes turbofan  12 , compressor section  14 , combustion section  16  and turbine section  18 . Compressor section  14  includes low-pressure compressor  20  and high-pressure compressor  22 . Engine  10  also includes bypass section  26  with structural guide vanes  28  and strut rods  30  extending between outer casing  32  and center body  34 . Center body  34  houses compressor section  14 , combustion section  16  and turbine section  18 . 
         [0012]    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  24 A, which drives low pressure compressor  20  and turbofan  12 , and outer shaft  24 B which drives high pressure compressor  22 . 
         [0013]    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. 
         [0014]      FIG. 2A  is a front perspective view of structural members of fan exit case C with structural guide vanes  28  and strut rods  30 .  FIG. 2B  is a view similar to  FIG. 2A , but with the structural guide vanes  28  removed.  FIGS. 2A and 2B  show outer casing  32 , structural guide vanes  28  (with inner ends  36  and outer ends  38 ), strut rods  30  (with inner ends  40  and outer ends  42 ) and portions of center body  34 . Vanes  28  can be made of a high strength material, such as aluminum (including aluminum alloys), a carbon epoxy composite or different materials depending on system requirements. Rods  30  can be made of a high-strength, low weight material, such as titanium or aluminum (including alloys). 
         [0015]    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. 
         [0016]    In  FIGS. 2A and 2B , rods  30  are connected in an A-frame arrangement so that outer ends  42  of two rods  30  connect to outer casing  32  at a point close together. This point is also at or near where structural guide vanes  28  are connected to outer casing  32  at outer ends  38 . This embodiment contains three A-frame arrangements of strut rods  30 , but different systems can have more or fewer A-frames depending on system requirements. Strut rods  30  can be aerodynamically shaped, for example, with a teardrop shaped cross section. 
         [0017]    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. 
         [0018]    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 . 
         [0019]      FIG. 3  is a perspective view of a back side of a second embodiment of fan exit case C′.  FIG. 4  is a perspective view of a back side of a third embodiment of fan exit case C″.  FIGS. 3 and 4  include outer casing  32 , guide vanes  28  (with inner ends  36  and outer ends  38 ), strut rods  30  (with inner ends  40  and outer ends  42 ), and center body  34 . Structural guide vanes  28  are connected to center body  34  and to outer casing  32  and are swept back. Strut rods  30  are connected to center body  34  and to outer casing  32 . 
         [0020]    In these embodiments, rods  30  are connected in H-frame arrangements, forming a sort of “H” around center body  34 . In  FIG. 3 , rods  30  are connected roughly vertically from side portions of center body  34  (not radially) to outer casing  32 . In  FIG. 4 , rods  30  are connected tangentially to center body  34 . Each of these arrangements connects strut rods  30  outer ends  42  at locations close to the connection of outer ends  38  of structural guide vanes  28 . This allows strut rods  30  to add stability and torsional strength to structural guide vanes  28 . It also allows structural guide vanes  28  to be swept back and still able to withstand engine loads while minimizing noise. 
         [0021]    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. 
         [0022]    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. 
         [0023]    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.