Abstract:
A gas turbine engine compressor has a number of shroud rings, at least a bleed one of which defines a number of bleed ports. A structural hub is downstream of the shroud rings and secured relative to the shroud rings. A structural hub case extends from an aft joint with the structural hub to a fore joint with a joined one of the shroud rings and has a number of valve ports. At least a portion of the structural case extends structurally between the fore and aft joints. A valve element is shiftable between first and second conditions for respectively blocking and not blocking communication through the valve ports.

Description:
BACKGROUND OF THE INVENTION 
   (1) Field of the Invention 
   The invention relates to turbomachinery. More particularly, the invention relates to gas turbine engines having compressor bleeds. 
   (2) Description of the Related Art 
   Axial flow gas turbine engines include a compressor, a combustor and a turbine. A core flowpath for medium gases extends through these portions of the engine. During operation, the gases are pressurized in the compressor and fuel is added in the combustor. The fuel is burned to add energy to the pressurized gases. The hot, pressurized gases are expanded through the turbine to provide the work of hot, high pressure gases for subsequent use. Common gas turbine engine configurations divide the combustor and turbine into high and low speed/pressure sections whose blades are mounted on respective high and low speed spools. Additionally, a broad spectrum of turbine engines provide a bypass wherein the turbine (typically the low speed section) drives a fan which, in turn, propels gas along a flowpath bypassing the core flowpath. 
   Under certain conditions, air is bled from a compressor section for one or more purposes. The air may be bled for use such as in cooling. Alternatively, however, the air may be bled to reduce the load on the associated turbine section under certain operating conditions. An exemplary such operating condition is a transient startup condition. Such load-reducing bleeds may be controlled by a bleed valve. U.S. Pat. No. 6,092,987 of Honda et al., the disclosure which is incorporated by reference herein, discloses a stator assembly having a valve ring moveable between first and second conditions in which the ring respectively blocks and opens communication through bleed openings in a stator housing. Shifting between the first and second conditions is via a combination of rotation and longitudinal translation so as to provide a mechanical advantage. Nevertheless, there remains room for further improvement in bleed valve technology. 
   SUMMARY OF THE INVENTION 
   Accordingly, one aspect of the invention involves a gas turbine engine having a fan and a compressor. The compressor is along a core flowpath and has a number of rows of blades, a number of rows of vanes, and a number of shroud rings. At least a bleed one of the shroud rings defines a number of bleed ports. A structural hub is downstream of the shroud rings and is secured relative to the shroud rings. A structural case extends from an aft joint with the structural hub to a fore joint with a joined one of the shroud rings. The structural case has a number of valve ports. At least a portion of the structural case extends structurally between fore and aft joints. A valve element is shiftable between first and second conditions. In the first condition the valve element blocks communication through the valve ports. In the second condition the valve element does not block that communication. 
   In various implementations, the joined one of the shroud rings may not be the bleed one of the shroud rings. The bleed one of the shroud rings may comprise a shroud ring of an exit guide vane assembly and a bleed duct. The exit guide vane assembly may have a number of duct portions associated with aft portions of the bleed ports. The bleed duct may have a number of duct portions associated with fore portions of the bleed ports. The joined one of the shroud rings may be immediately upstream of the bleed one of the shroud rings. The valve element may be so shiftable via a combined circumferential rotation and longitudinal translation. The valve element may carry an outboard aft seal and an inboard fore seal for sealing with the structural case in the first condition. A bleed flowpath through the bleed ports and the valve ports may further extend through the structural hub to join a fan bypass flow. The structural hub may contain at least one fan exit guide vane. The bleed flowpath may join a fan bypass flow downstream of the fan exit guide vane. 
   Another aspect of the invention involves a gas turbine engine wherein a structural case extends from an aft joint with a structural hub to a fore joint with a joined one of a number of shroud rings. The structural case may have a number of valve ports. At least a portion of the structural case may extend as a continuous piece between the fore and aft joints. 
   In various implementations, the joined one of the shroud rings may be immediately upstream of a bleed one of the shroud rings. The structural hub may carry a number of fan exit guide vanes. 
   Another aspect of the invention involves a method for assembling a gas turbine engine. The method involves assembling an exit guide vane assembly including an aftmost of a number of shroud rings to a structural hub. A structural case is assembled to the structural hub. An assembly of the shroud rings is assembled to the structural case with at least one of the shroud rings being at least partially inserted within the structural case. 
   In various implementations, at least one fan exit guide vane may be preassembled with the structural hub. The aftmost of the shroud rings may have a number of duct portions associated with aft portions of the bleed ports. A penultimate shroud ring may have a number of duct portions associated with fore portions of the bleed ports. The valve element may be assembled to the structural case after the structural case is assembled to the structural hub. 
   The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a longitudinal radial sectional view of a gas turbine engine according to the principles of the inventions. 
       FIG. 2  is a partial longitudinal radial sectional view of a low speed/pressure compressor section of the engine of  FIG. 1 . 
   

   Like reference numbers and designations in the various drawings indicate like elements. 
   DETAILED DESCRIPTION 
     FIG. 1  shows a gas turbine engine  20  having a case assembly  22  containing concentric high and low pressure rotor shafts  24  and  25 . The shafts are mounted within the case for rotation about an axis  500  which is normally coincident with central longitudinal axes of the case and shafts. The high pressure rotor shaft  24  is driven by the blades of a high pressure turbine section  26  to in turn drive the blades of a high pressure compressor  27 . The low pressure rotor shaft  25  is driven by the blades of a low pressure turbine section  28  to in turn drive the blades of a low pressure compressor section  29  and a fan  30 . Air passes through the engine along a core flowpath  502  sequentially compressed by the low and high compressor sections  29  and  27 , then passing through a combustor  32  wherein a portion of the air is combusted along with a fuel, and then passing through the high and low turbine sections  26  and  28  where work is extracted. Additional air is driven by the fan along a bypass flowpath  504 . 
     FIG. 2  shows details of the low speed/pressure compressor section  29 . The section has a number of blade rows including a downstreammost last row of blades  40  and a penultimate row of blades  42  thereahead separated by a row of stator vanes  44 . The blades&#39; roots are mounted to one or more rotating disks  46  of the low speed spool. The vane outboard portions are mounted to associated shrouds. 
   A compressor shroud assembly  47  essentially provides the outboard boundary of the core flowpath  502 . The assembly  47  includes a number of annular shrouds generally assembled end-to-end. Each of the shrouds may, itself, be segmented circumferentially, with the circumferential segments secured end-to-end.  FIG. 2  shows a shroud  48  carrying the outboard end of the vanes  44 . The exemplary shroud  48  has bolting flanges  49  and  50  for structurally bolting the shroud to similar flanges of shrouds immediately upstream and downstream thereof. The penultimate and last shrouds  51  and  52  downstream thereof combine to form an exit/bleed shroud. The shroud  52  is unitarily formed or alternatively integrated with a row of exit stator vanes  53  downstream of the last row of blades  40 . Exemplary shrouds  51  and  52  may be a full annulus or may be split or segmented for assembly/manufacturing ease. The shrouds  51  and  52  combine to define a circumferential array of bleed ports  54  with bleed offtake ducts  56  extending outboard therefrom into a common annular bleed plenum  58 . A downstream/trailing portion of the shroud  51  defines leading portions of the ducts  56  and an upstream leading portion of the shroud  52  defines trailing portions of the ducts  56 . 
   The shroud  51  has an upstream bolting flange  60  mounted to the bolting flange  50  thereahead. The shroud  52  has a downstream bolting flange  62  mounted to an inboard upstream bolting flange  64  on a radial circumferential web  66  of a fan hub or rotor support frame  68  which forms a principal structural component of the engine. The fan hub  68  may be fabricated by welding together several circumferentially stacked pieces. In the illustrated embodiment, an inboard piece includes a circumferential array of struts  70  extending outboard to a shroud portion  72 . Fore and aft circumferential webs  66  and  74  extend from the shroud portion  72  and are connected by longitudinal webs  76 . An outboard piece  80  is joined to inboard piece  82  along a weld  84 . The inboard piece has an outboard longitudinal circumferential web  86  and the outboard piece has inboard and outboard longitudinal circumferential webs  88  and  90 . In the exemplary embodiment, the fore and aft radial circumferential webs  66  and  74  extend along both pieces and may alternatively be referenced as combined webs of the two pieces. For reference, certain areas of these webs identified as flanges may be thickened or otherwise reinforced although alternatively the term web may be used to identify the section of web material between the flanges. 
   At its outboard end, the outboard piece  80  is secured to root portions  92  of fan exit guide vanes  94  via fore and aft hub bolting flanges  96  and  98  and corresponding fore and aft vane bolting flanges  97  and  99 . 
   A structural case  100  has an inboard surface defining an outboard extreme of the bleed plenum  58 . The structural case  100  extends from a forward/upstream bolting flange  102  to an aft/downstream bolting flange  104 . The upstream bolting flange  102  is mounted to an intermediate bolting flange  106  of the shroud  48 . The downstream bolting flange  104  is mounted to a bolting flange  108  on the web  66  outboard of the web  74  and just inboard of the weld  84 . The structural case  100  has a plurality of apertures  110  which may be selectively blocked by an annular valve element  112 . The valve element  112  may be shiftable between open and closed conditions (the closed condition being shown) respectively exposing and blocking the apertures or ports  110  via a combined rotation and longitudinal translation as in the aforementioned &#39; 987  patent and may be provided with an appropriate actuator (not shown) to effect movement between such conditions. 
   A bleed flowpath  506  extends through the bleed port  54  and duct  56  into the bleed plenum  58 . With the valve element  112  in its open condition, the bleed flowpath further continues through the apertures  110  and into an outboard plenum  114 . The outboard plenum is generally bounded by the structural case  100  and shroud assembly  47  thereahead on the inboard side, the web  66  along the outboard web piece  80  on the aft side, and a flow divider (splitter)  116  separating the outboard plenum from the bypass flowpath  504 . Therefrom, the flowpath proceeds through a port or window  120  in the forward web  66  along the outboard piece  80  of the structural hub  68 . The flowpath proceeds through a window  122  in the outboard web  90 . The flowpath may then pass between aft bolting flanges  99  of adjacent exit guide vanes  94  inboard of their platforms  124  to, downstream of trailing edges  126  of such platforms, and merge with the bypass flowpath  504 . 
   The use of a structural case having the valve ports  110  (as opposed to placing the valve ports in a totally separate non-structural member) may facilitate an advantageous assembly process. The exist guide vanes may be preassembled to the structural hub. The last shroud  52  may then be bolted to the hub. The structural case may then be bolted to the hub. The shrouds  51  and  48  may be preassembled as may be the shrouds thereahead. This shroud subassembly may then be assembled to the structural case with the process including an insertion of the shroud  51  and a portion of the shroud  48  within the structural case followed by securing with bolts. The valve element (or elements)  112  may have been preassembled with the structural case or may be assembled after assembly of the case to the hub or after assembly of the shroud subassembly to the case. Thereafter the splitter may be installed. 
   One or more embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, the principles may be applied as a modification of a preexisting engine configuration. In such a situation, details of the preexisting configuration would influence details of the particular implementation. Accordingly, other embodiments are within the scope of the following claims.