Abstract:
An inner diameter vane shroud for use in a gas turbine engine is comprised of lightweight cast forward and aft shroud components. The forward and aft shroud components are made with an investment casting technique that creates a hollow cavity that runs in a circumferential direction through each component. The forward and aft shroud components are matable to form sockets that receive inner diameter ends of variable stator vanes.

Description:
This invention was made with U.S. Government support under contract number N00019-02-C-3003 awarded by the United States Navy, and the U.S. Government may have certain rights in the invention. 

   CROSS-REFERENCE TO RELATED APPLICATION(S) 
   The present application is related to the following copending applications filed on the same day as this application: “RACK AND PINION VARIABLE VANE SYNCHRONIZING MECHANISM FOR INNER DIAMETER VANE SHROUD” by inventors J. Giaimo and J. Tirone III (application Ser. No. 11/185,622); “SYNCH RING VARIABLE VANE SYNCHRONIZING MECHANISM FOR INNER DIAMETER VANE SHROUD” by inventors J. Giaimo and J. Tirone III (application Ser. No. 11/185,623); “GEAR TRAIN VARIABLE VANE SYNCHRONIZING MECHANISM FOR INNER DIAMETER VANE SHROUD” by inventors J. Giaimo and J. Tirone III (application Ser. No. 11/185,624); and “INNER DIAMETER VARIABLE VANE ACTUATION MECHANISM” by inventors J. Giaimo and J. Tirone III (application ser. No. 11/185,995). All of these applications are incorporated herein by this reference. 
   BACKGROUND OF THE INVENTION 
   This invention relates generally to gas turbine engines and more particularly to vane shrouds for use in such engines. 
   Gas turbine engines operate by combusting a fuel source in compressed air to create heated gases with increased pressure and density. The heated gases are ultimately forced through an exhaust nozzle, which is used to step up the velocity of the exiting gases and in-turn produce thrust for driving an aircraft. The heated gases are also used to drive a turbine for rotating a fan to provide air to a compressor section of the gas turbine engine. Additionally, the heated gases are used to drive a turbine for driving rotor blades inside the compressor section, which provides the compressed air used during combustion. The compressor section of a gas turbine engine typically comprises a series of rotor blade and stator vane stages. At each stage, rotating rotor blades push air past the stationary stator vanes. Each rotor/stator stage increases the pressure and density of the air. Stators serve two purposes: they convert the kinetic energy of the air into pressure, and they redirect the trajectory of the air coming off the rotors for flow into the next compressor stage. 
   The speed range of an aircraft powered by a gas turbine engine is directly related to the level of air pressure generated in the compressor section. For different aircraft speeds, the velocity of the airflow through the gas turbine engine varies. Thus, the incidence of the air onto rotor blades of subsequent compressor stages differs at different aircraft speeds. One way of achieving more efficient performance of the gas turbine engine over the entire speed range, especially at high speed/high pressure ranges, is to use variable stator vanes which can optimize the incidence of the airflow onto subsequent compressor stage rotors. 
   Variable stator vanes are typically circumferentially arranged between an outer diameter fan case and an inner diameter vane shroud. In split shroud designs, the vane shroud is divided into a forward and aft component, with inner diameter ends of the variable stator vanes secured between the two components. Traditionally, the forward and aft components of the inner diameter vane shroud have been fabricated from solid metal pieces. These solid metal vane shrouds are typically used in ground test engines where weight is not a concern. However, these solid vane shrouds are not suitable for use in production engines used in aircraft where weight is of the utmost concern. Thus, there is a need for a flight-weight inner diameter variable vane shroud. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention is directed toward an inner diameter vane shroud for receiving inner diameter ends of stator vanes in a turbine engine. The inner diameter vane shroud includes a forward shroud component and an aft shroud component. The forward shroud component has a defined length and includes a forward hollow channel running the length of the forward shroud component. The aft shroud component has a defined length and includes an aft hollow channel running the length of the aft shroud component. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a partially cut away front view of a stator vane section of a gas turbine engine in which the present invention is used. 
       FIG. 2  shows a close up of a stator vane array positioned between a fan case and the inner diameter vane shroud of the present invention. 
       FIG. 3A  shows section  3 - 3  of  FIG. 2  showing a cross section of the inner diameter vane shroud between the vane sockets. 
       FIG. 3B  shows an exploded view of the cross section of the inner diameter vane shroud of  FIG. 3A . 
       FIG. 4A  shows section  4 - 4  of  FIG. 2  showing a cross section of the inner diameter vane shroud at the vane sockets. 
       FIG. 4B  shows an exploded view of the cross section of the inner diameter vane shroud of  FIG. 4A . 
   

   DETAILED DESCRIPTION 
     FIG. 1  shows a partially cut away front view of stator vane section  10  of a gas turbine engine in which the present invention is used. Stator vane section  10  comprises fan case  12 , vane shroud  14 , variable vane array  16  and actuator  18 . Vane shroud  14  is comprised of forward vane shroud component  20  and aft vane shroud component  22 , which form inner diameter vane sockets  24 . A half-socket, or a recess, is located on each of forward shroud portion  20  and aft shroud portion  22  to form socket  24 . In  FIG. 1 , only a portion of forward vane shroud  20  is shown so that the interior of sockets  24  can be seen. Inner diameter vane shroud  14  can be constructed in component sizes less than the entire circumference of inner diameter vane shroud. In one embodiment, as shown in  FIG. 1 , forward vane shroud component  20  is made of sections approximately one sixth (i.e. 60°) of the circumference of inner diameter vane shroud  14 , and aft shroud component  22  is made of sections one half (i.e. 180°) the circumference of inner diameter vane shroud  14 . 
   Variable vane array  16  is comprised of drive vanes  26  and a plurality of follower vanes  28 . Drive vanes  26  and follower vanes  28  are connected inside inner diameter vane shroud  14  by a synchronizing mechanism such as described in the copending related applications referred to above. Thus, when actuator  18  rotates drive vanes  26 , follower vanes  28  rotate a like amount. 
   Typically, follower vanes  28  encircle the entirety of vane shroud  14 . Only a portion of variable vane array  16  is shown so that sockets  24  can be seen. Drive vanes  26  and follower vanes  28  are rotatably mounted at the outer diameter of stator vane section  10  in fan case  12 , and at the inner diameter of stator vane section  10  in vane shroud  14 . The number of drive vanes  26  varies in other embodiments and can be as few as one. In one embodiment, variable vane array  16  includes fifty-two follower vanes  28  and two drive vanes  26 . Drive vanes  26  are similar in construction to follower vanes  28 . In one embodiment, drive vanes  26  are of heavy duty construction to withstand forces applied by actuator  18 . 
   Stator vane section  10  is typically located in a compressor section of a gas turbine engine downstream of, or behind, a rotor blade section. Air is forced into stator vane section  10  by a preceding rotor blade section or by a fan. The air that passes through stator vane section  10  typically passes on to an additional rotor blade section. Drive vanes  26  and follower vanes  28  rotate along their respective radial positions in order to control the flow of air through the compressor section of the gas turbine engine. 
     FIG. 2  shows a close up of variable vane array  16  between fan case  12  and vane shroud  14 . Drive vanes  26  and follower vanes  28  are rotatable in sockets  24  of inner diameter vane shroud  14 . Section  3 - 3  is taken at a position along inner diameter vane shroud  14  between sockets  24 . Between sockets  24 , forward shroud component  20  and aft shroud component  22  are fastened together to form inner diameter vane shroud  14 . Section  44  is taken at a position along inner diameter vane shroud  14  where inner diameter end of follower vane  28 A is inserted in socket  24 A. Forward shroud component  20  and aft shroud component  22  come together to form sockets  24  for securing the inner ends of variable vane array  16 . 
     FIG. 3A  shows section  3 - 3  of  FIG. 2  showing a cross section of inner diameter vane shroud  14  between vane sockets  24 .  FIG. 3B  shows an exploded view of the cross section of the inner diameter vane shroud of  FIG. 3A .  FIGS. 3A and 3B  will be discussed concurrently. Inner diameter vane shroud  14  includes forward shroud component  20 , aft shroud component  22 , forward hollow region  30 , aft hollow region  32 , hole  34 , fastener  36 , locking insert  37 , opening  38 , cap  39 , recess  40  and hole  42 . 
   Forward hollow region  30  and aft hollow region  32  are formed during the manufacture of forward vane shroud component  20  and aft vane shroud component  22  using investment casting techniques known in the art. In one embodiment, ceramic cores are placed in the mold during the casting of forward shroud component  20  and aft shroud component  22 . The ceramic cores are removed after molds of forward vane shroud component  20  and aft vane shroud component  22  have solidified and cooled in order to create forward hollow region  30  and aft hollow region  32 , respectively. Forward hollow region  30  and aft hollow region  32  reduce the amount of material required to produce forward shroud component  20  and aft shroud component  22  thereby reducing the weight of inner diameter vane shroud  14 . Inner diameter vane shroud  14  remains sturdy enough to secure drive vanes  26  and follower vanes  28  during operation of a gas turbine engine. Lightweight cast forward shroud component  20  and aft shroud component  22  are also capable of being machined to meet the design requirements of the stator vanes and gas turbine engine with which they are to be used. 
   Forward vane shroud component  20  is cast with opening  38 , which provides access to forward hollow region  30 . In other embodiments, opening  38  can be produced with machining procedures after casting. Additional features of forward vane shroud component  20  are machined into forward vane shroud component  20  after casting. For example, recess  40  can be machined into forward shroud component  20  and aft shroud component  22  as a weight reduction measure. Hole  34  and hole  42  can be produced with additional machining steps. The exact shape and form of hole  34  and recess  40  depend on specific design requirements of gas turbine engine in which inner diameter vane shroud  14  will be used. Forward vane shroud component  20  and aft vane shroud component  22  can be made in segments less than entire circumference of the final required inner diameter vane shroud  14 . In one embodiment, forward vane shroud component  20  is comprised of approximately one sixth circle (i.e. 60°) segments and aft vane shroud component  22  is comprised of approximately half circle (i.e. 180°) segments for use in split fan case designs. 
   Inner diameter vane shroud  14  is assembled by securing forward shroud component  20  to aft shroud component  22  with fastener  36 . Locking insert  37  is placed inside hole  34  across from hole  42 . Fastener  36  is inserted through forward hollow region  30 , through hole  42  and into locking insert  37  of hole  34 . Cap  39  is placed over opening  38  to close it off and provide an aerodynamic surface to the front of forward vane shroud component  20 . Drive vanes  26  and follower vanes  28  are inserted into sockets  24  before assembly of forward shroud component  20  and aft shroud component  22 . 
     FIG. 4A  shows section  4 - 4  of  FIG. 2  showing a cross section of inner diameter vane shroud  14  at vane sockets  24 .  FIG. 4B  shows an exploded view of the cross section of the inner diameter vane shroud of  FIG. 4A .  FIGS. 4A and 4B  will be discussed concurrently. Inner diameter vane shroud  14  includes forward shroud component  20 , aft shroud component  22 , socket  24 A, forward hollow region  30 , aft hollow region  32 , recess  33 , opening  38 , and cap  39 . Follower vane  28 A includes trunnion  43 , which is pivotably located in socket  24 A of inner diameter vane shroud  14 . Socket  24 A is comprised of recess  25 A and recess  25 B. Forward vane shroud component  20  and aft vane shroud component  22  come together to form socket  24 A when forward vane shroud component  20  is secured to aft vane shroud component  22  using fastener  36  as shown in  FIG. 3A . Socket  24 A is shaped to have a profile for accepting the profile of trunnion  42 . Thus, trunnion  43  is secured in socket  24 A and able to rotate in socket  24 A. Recess  33  is molded directly into or machined into aft shroud component  22  as a weight reduction measure. 
   Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.