Abstract:
A splitter apparatus for a gas turbine engine includes: a splitter including: an annular outer wall which defines a convex-curved leading edge at a forward end thereof; an annular floorplate positioned radially inboard of the outer wall; and an annular first bulkhead spanning between the outer wall and the floorplate. The outer wall, the floorplate, and the bulkhead collectively define an annular splitter plenum positioned adjacent the leading edge of the outer wall. At least one exhaust passage formed in the outer wall extends past the floorplate and communicates with the exterior of the splitter. At least one jumper tube assembly passes through the first bulkhead, each configured to pass air flow from the exterior of the splitter into the plenum.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of provisional application 61/438,251, filed Jan. 31, 2011. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention relates generally to turbine engine structures and more particularly to materials and designs for improving anti-icing characteristics from such structures. 
         [0003]    One common type of aircraft powerplant is a turbofan engine, which includes a turbomachinery core having a high pressure compressor, combustor, and high pressure turbine in serial flow relationship. The core is operable in a known manner to generate a flow of propulsive gas. A low pressure turbine driven by the core exhaust gases drives a fan through a shaft to generate a propulsive bypass flow. The low pressure turbine also drives a low pressure compressor or “booster” which supercharges the inlet flow to the high pressure compressor. 
         [0004]    Certain flight conditions allow for ice build up on the leading edge structures, and in particular, the fan and booster flowpath areas of the engine. One specific leading edge structure of interest is the engine&#39;s booster splitter. The splitter is an annular ring with an airfoil leading edge that is positioned immediately aft of the fan blades. Its function is to separate the airflow for combustion (via the booster) from the bypass airflow. 
         [0005]    It is desired to minimize ice build up and shed volume from the splitter during an icing event. This in turn minimizes risk of compressor stall and compressor mechanical damage from the ingested ice. 
         [0006]    It is known to heat engine structures for anti-icing. However, because the splitter is exposed to fan by-pass air, injection of hot air directly into the splitter would lead to insufficient heating at the nose due to heat loss to the fan air. 
         [0007]    Accordingly, there is a need for a splitter which is efficiently heated so as to be resistant to ice buildup. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    This need is addressed by the present invention, which provides a splitter having an internal plenum supplied with heated air to reduce ice buildup, promote ice release, and reduce shedding of large ice pieces. 
         [0009]    According to one aspect of the invention, a splitter apparatus for a gas turbine engine includes: a splitter including: an annular outer wall which defines a convex-curved leading edge at a forward end thereof; an annular floorplate positioned radially inboard of the outer wall; and an annular first bulkhead spanning between the outer wall and the floorplate. The outer wall, the floorplate, and the bulkhead collectively define an annular splitter plenum positioned adjacent the leading edge of the outer wall. At least one exhaust passage formed in the outer wall extends past the floorplate and communicates with the exterior of the splitter. A plurality of jumper tube assemblies passing through the first bulkhead, each configured to pass air flow from the exterior of the splitter into the plenum. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The invention may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which: 
           [0011]      FIG. 1  is a schematic half cross-sectional view of a gas turbine engine incorporating a heated booster splitter constructed according to an aspect of the present invention; 
           [0012]      FIG. 2  is a half-sectional view of a splitter shown in  FIG. 1  and surrounding structures; 
           [0013]      FIG. 3  is another half-sectional view of the splitter shown in  FIGS. 1 and 2  and surrounding structures; and 
           [0014]      FIG. 4  is a schematic diagram showing the components used to supply heated air to the splitter. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,  FIG. 1  depicts a known type of turbofan engine  16  mounted in a nacelle  18 . While the present invention will be described further in the context of a turbofan engine, it will be understood that the principles contained to other types of engines, such as turbojet or turboshaft engines, or other kinds of leading edge structures. 
         [0016]    The engine  16  has a longitudinal axis “A” and includes conventional components including a fan  24 , a low pressure compressor or “booster”  26  and a low pressure turbine (“LPT”)  28 , collectively referred to as a “low pressure system”, and a high pressure compressor (“HPC”)  30 , a combustor  32 , and a high pressure turbine (“HPT”)  34 , collectively referred to as a “gas generator” or “core”. Various components of the nacelle  18 , and stationary structures of the engine  16 , including a core nacelle  36 , cooperate to define a core flowpath marked with an arrow “F”, and a bypass duct marked with an arrow “B”. 
         [0017]    A stationary annular booster splitter  38  (or simply “splitter”) is positioned at the forward end of the core nacelle  36 , between the bypass duct B and the core flowpath F. The splitter  38  may be a single continuous ring, or it may be built up from arcuate segments. While a variety of materials such as metal alloys and composites may be used, the splitter  38  in this example is constructed from a known titanium alloy. 
         [0018]    The structure of the splitter  38  is shown in more detail in  FIGS. 2 and 3 . The splitter  38  has an annular outer wall  40  with a convex-curved, tapered shape that defines a flowpath surface  42 . The flowpath surface  42  includes a radially-outward-facing portion and a radially-inward-facing portion; the two portions are demarcated by an aerodynamic convex-curved leading edge  44  at the forward end of the splitter  38 . A radially-aligned annular aft bulkhead  46  is disposed at the aft end of the splitter  38 . A radially-aligned annular forward bulkhead  48  is disposed approximately halfway between the aft bulkhead  46  and the leading edge  44 . The outer wall  40  and bulkheads  46  and  48  could all be constructed as one integral component. The components surrounding and positioned adjacent to the splitter  38  may be made from materials such as metal alloys or composite materials (for example, carbon-fiber epoxy composites). 
         [0019]    An annular, axially-aligned, aft-facing groove  50  is defined by the outer wall  40  just aft of the leading edge  44 . An annular step  52  is formed just aft and radially outboard of the groove  50 . 
         [0020]    An annular floorplate  54  extends axially between the outer wall  40  and the forward bulkhead  48 . A forward edge of the floorplate  54  is received in the step  52 . The floorplate  54  may be joined to the splitter  38  by fasteners, welding or brazing, or adhesives. Collectively, the forward portion of the outer wall  40 , the forward bulkhead  48 , and the floorplate  54  define a continuous 360 degree splitter plenum  56  adjacent the leading edge  44 . 
         [0021]    The splitter  38  is mounted to an annular outer band  58  which circumscribes a row (i.e. a radial array) of airfoil-shaped booster inlet guide vanes  60 . Specifically, a forward rail  62  of the outer band  58  is received in the groove  50 . The aft bulkhead  46  bears against and is secured to a radially-extending annular flange  64  of the outer band  58  or adjacent stationary structure, for example using bolts or other mechanical fasteners. 
         [0022]    A resilient annular seal  66  is disposed between the outer band  58  and the floorplate  54 , near the forward end of the floorplate  54 , and serves to mitigate airflow leakage between the floorplate  54  and the outer band  58 . In the illustrated example the seal  66  has a hollow cross-section. 
         [0023]    An annular array of spaced-apart shallow slots  68  or other exhaust passages are formed in the inner surface of the outer wall  40  behind the leading edge  44  and adjacent the forward rail  62  of the outer band  58 . The slots  68  define a generally “U”-shaped path from the splitter plenum  56  around the forward rail  62  and communicating with the inboard surface of the outer band  58 , through a gap between the outer band  58  and the outer wall  40 . The slots  68  are shaped, sized, and oriented to return heating air to the turbine flowpath at an angle and location selected to minimize aerodynamic disruption. In the illustrated example there is one slot  68  located between each inlet guide vane  60 . 
         [0024]      FIG. 4  shows schematically components which may be used to supply a uniform flow of heated bleed air to the splitter plenum  56 . An annular manifold  70  with wyes (also seen schematically in  FIG. 1 ) is positioned outside the booster  26  just forward of an annular fan hub frame  72  of the engine  16 . Struts  73  extend radially outward from the fan hub frame  72  to join the nacelle  18 . An annular array of feed pipes  74  (which may be thermally insulated) extend axially from the manifold  70  to the splitter  38 . A jumper tube assembly  76  (seen in  FIG. 2 ) extends forward from each feed pipe  74 . 
         [0025]    The engine  16  includes a conventional engine anti-icing duct  78  which takes high-temperature pressured bleed air from the high pressure compressor  30  (in this case from the seventh compressor stage), under the control of a pressure regulating shut-off valve  80 . This air is ducted through a pressure regulating valve  82  to the engine&#39;s inlet and other conventionally heated structures. A takeoff duct  84  branches from the anti-icing duct  78  to an active valve  86  which controls flow through a splitter feed duct  88 . The splitter feed duct  88  passes through the fan hub frame  72  (through a boss  90 ) and feeds the manifold  70 . The active valve  86  is controlled (for example using a electropneumatic, hydraulic, or electronic controller, not shown) according to an appropriate control law which provides heated air flow under the necessary conditions. In this example, redundant pressure transducers  92  are provided in the splitter feed duct  88  downstream of the active valve  86 . They may be used to verify operation of the active valve  86 . For example, if the active valve is commanded “open”, but no pressure increase is sensed by the transducers  92 , this is an indication that the active valve  86  has failed to actually open. 
         [0026]    The jumper tube assemblies  76  are shown in more detail in  FIG. 2 . Each assembly  76  includes a jumper tube  94 . The forward end  96  of the jumper tube  94  passes through the forward bulkhead  48  and at its aft end  98  passes through the aft bulkhead  46  and couples it to the feed pipe  74 . The feed pipes  74  and jumper tube assemblies  76  are arranged to provide circumferentially-consistent air flow to the splitter plenum  56 . In the illustrated example there are six equally-spaced feed pipes  74  with corresponding jumper tube assemblies  76 . 
         [0027]    The diameter, length, material, surface finishes and other characteristics of the ducting including the takeoff duct  84 , splitter feed duct  88 , manifold  70 , feed pipes  74  and jumper tube assemblies  76  may be selected according to known engineering principles to provide appropriate pressure, velocity and flow rate to feed the splitter plenum  56  as needed for anti-icing operation. 
         [0028]    In operation, the engine  16  will be exposed to icing conditions, namely the presence of moisture in temperatures near the freezing point of water. Ice will naturally tend to form on the leading edge structures including the splitter  38 . As the ice mass builds up, it protrudes into the air flow and increasing aerodynamic (drag) forces act on it, eventually causing portions of it to shed from the splitter  38 . 
         [0029]    When necessary to avoid ice buildup or to cause shedding of accreted ice, the valves  80  and  86  are opened, permitting high-temperature pressurized air to enter the splitter feed duct  88  and manifold  70 . The valve  86  may be used to reduce the pressure as needed. The heated air is fed into the splitter plenum  56  through the jumper tube assemblies  76 . The air will circulate freely around the circumference of the splitter plenum  56 , heating the outer wall  40 , with the heating effect concentrated near the leading edge  44 , where ice shedding is of the greatest concern. This has the effect of reducing or preventing ice buildup and/or causing shedding of already attached ice. The splitter plenum  56  may be heated in such a way that ice sheds as relatively small particles which have a reduced tendency to affect engine operation. 
         [0030]    The spent heating air exits the splitter plenum  56  through the slots  68  which redirect the air in such a way as to minimize aerodynamic losses, such as by ejecting it parallel to the streamlines flowing past the inlet guide vanes  60 . In this way the cycle penalty for using bleed air to heat the splitter  38  is reduced. 
         [0031]    The splitter configuration described above reduces exposure to the fan air as well as provides a means to distribute heat circumferentially from the hot air injection sites. The invention described herein provides a means of unlimited operation in cold weather. Without the booster splitter plenum  56 , insufficient heat would lead to ice build-up on the splitter lip during airplane ground operation. Upon run up to take-off power the ice shed would produce a stall thus delaying plane departure. A secondary benefit of the booster splitter plenum  56  is to protect the composite hardware aft of the splitter  38 . Bleed air temperatures from the high pressure compressor  30  can reach 530° C. (1000° F.). By moving the hot air away from the less temperature capable composite parts, this ensures the composite does not degrade. The splitter plenum design reduces the size and weight of tubing required to heat the splitter  38  as well as the temperature and flow of bleed air needed. 
         [0032]    The foregoing has described a heated booster splitter plenum for a gas turbine engine. While specific embodiments of the present invention have been described, it will be apparent to those skilled in the art that various modifications thereto can be made without departing from the spirit and scope of the invention. Accordingly, the foregoing description of the preferred embodiment of the invention and the best mode for practicing the invention are provided for the purpose of illustration only.