Abstract:
A turbine engine stator segment has an outer wall segment with inboard and outboard surfaces. An inner wall segment has inboard and outboard surfaces essentially sharing an axis with those of the outer wall segment. Airfoils forming a sector of a first airfoil stage extend between the wall segments. The outboard wall segment has a compressor bleed port mounted at least along a forward edge by a lip projecting rearward and radially outward. The lip has inner and outer surfaces and a rim and projects radially beyond an adjacent portion of the outer wall segment.

Description:
U.S. GOVERNMENT RIGHTS  
       [0001] The invention was made with U.S. Government support under contract N-00019-02-C-3003 awarded by the U.S. Navy. The U.S. Government has certain rights in the invention. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    (1) Field of the Invention  
           [0003]    This invention relates to turbine engine compressors, and more particularly to compressor bleeds from high pressure compressors.  
           [0004]    (2) Description of the Related Art  
           [0005]    Multi-stage axial flow compressors are typically used in gas turbine engines to supply high pressure gas for combustion and subsequent expansion in a coaxial multi-stage turbine. In normal operation, the turbine, in turn, drives the compressor. Many engine configurations split the compressor and turbine into high and low pressure/speed sections whose blades are mounted on respective high and low speed spools. A typical engine core flowpath extends through the low compressor, high compressor, combustor, high turbine, and low turbine in sequence.  
           [0006]    Compressor air is commonly bled from the core flowpath through bleed ports in the outer wall surrounding the flowpath. The bleed air may be used for several purposes. It may be directed for internal cooling of the turbine blades and vanes. It may be directed to provide thermal and/or mechanical energy for external systems (e.g., aircraft HVAC, de-icing, cross-bleed engine starting, and the like). During start-up, a relatively downstream bleed (e.g., in the later stages of the high compressor) may limit backpressure and, thereby, reduce stall tendencies.  
         BRIEF SUMMARY OF THE INVENTION  
         [0007]    Accordingly, one aspect of the invention involves a turbine engine stator segment has an outer wall segment with inboard and outboard surfaces. An inner wall segment has inboard and outboard surfaces essentially sharing an axis with those of the outer wall segment. Airfoils forming a sector of a first airfoil stage extend between the wall segments. The outboard wall segment has a compressor bleed port mounted at least along a forward edge by a lip projecting rearward and radially outward. The lip has inner and outer surfaces and a rim and projects radially beyond an adjacent portion of the outer wall segment.  
           [0008]    The lip may project at least a height of 0.400 inch beyond adjacent portion of the outer wall segment. The lip may have a thickness of 0.06-0.09 inch. The outer wall segment outboard surface may have a recess at least immediately ahead of the lip. The lip may circumscribe the bleed port. The lip may be shorter along a trailing edge than along the forward (leading) edge. Along a majority of the lip inner surface extending from the bleed port forward edge, the lip inner surface may have an angle between 40° and 50° relative to the axis. The outer wall segment may include a number of bleed ports. Each bleed port may have a circumferential length of between 2.0 and 2.3 inch. The bleed port may be elongate in the circumferential direction about the axis. The segment may further include a second inner wall segment having inboard and outboard surfaces and a second plurality of airfoils forming a sector of a second airfoil stage and extending between the second inner wall segment and the outer wall segment. The first airfoil segment may be ahead of the bleed ports and the second behind. The segment may be formed essentially as a unitary casting of a nickel-based superalloy.  
           [0009]    Another aspect of the invention involves a turbine engine compressor. The compressor has a case having an axis, a number of rings of vanes, and a number of rings of blades alternating with the vane rings and coaxial therewith about the axis and mounted for rotation about the axis. The case has a core outboard wall having an inboard surface essentially locally bounding an outboard extreme of a core flowpath sequentially through the alternating rings of vanes and blades. At least one additional wall cooperates with the core outboard wall to bound a bleed air plenum outboard of the core flowpath. A number of bleed ports in the core outboard wall provide communication from the core flowpath to the bleed air plenum. A number of bleed port leading walls extend from the core outboard wall at a leading edge of associated bleed ports into the bleed air plenum and have port length to depth ratios of 2.5:1-3.5:1. The ratios may be 2.8-3.2. The case may be an assembly including a number of segments assembled longitudinally and circumferentially. The vanes may be unitarily formed with associated ones of the segments.  
           [0010]    Another aspect of the invention involves a method for modifying a turbine engine compressor. A first outer wall segment is removed and replaced with a replacement having bleed ports bounded along a forward edge by a lip projecting rearward and radially outward. The lip has inner and outer surfaces and a rim and projects at least a height radially beyond an adjacent portion of the outer wall of the second segment.  
           [0011]    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  
       [0012]    [0012]FIG. 1 is a partial longitudinal sectional view of a turbine engine high compressor.  
         [0013]    [0013]FIG. 1A is an enlarged view of a bleed port of the compressor of FIG. 1.  
         [0014]    [0014]FIG. 2 is a longitudinal sectional view of an alternate bleed port.  
         [0015]    [0015]FIG. 3 is a longitudinal sectional view of a second alternate bleed port.  
         [0016]    [0016]FIG. 4 is a view of a prior art engine stator segment.  
         [0017]    [0017]FIG. 5 is a view of a stator segment of the compressor of FIG. 1.  
         [0018]    Like reference numbers and designations in the various drawings indicate like elements.  
     
    
     DETAILED DESCRIPTION  
       [0019]    [0019]FIG. 1 shows a turbine engine high pressure/speed compressor  20 . The compressor has a case assembly  22  circumscribing a central longitudinal axis or centerline  500  (spacing not to scale). The exemplary compressor includes alternating rings of vanes  24 A- 24 F and blades  26 A- 26 F. The exemplary case  22  has a wall  30  having inboard and outboard surfaces  32  and  34 . The inboard surface defines an outboard boundary/wall of a core flowpath  502 . An inboard boundary/wall of the flowpath  502  is largely defined by platforms of the vanes and blades.  
         [0020]    The exemplary wall  30  is provided with a plurality of bleed ports  38  having inlets  40  and outlets  41  diverting a bleed flow  504  from the core flowpath  502  to a bleed manifold or plenum  42  circumscribing the wall  30  and inboard bounded by the surface  34  and outboard bounded by an interior surface  44  of a case second wall  46 . In the exemplary implementation, the ports  40  are circumferentially arrayed along the wall  30 . In the exemplary implementation, the bleed ports  38  fall between two vane stages  24 E and  24 F and, more particularly, between a vane stage  24 E and the following blade stage  26 E. In an exemplary implementation, the vane stage  24 E is the seventh stage (there being two additional stages in the low compressor and the inlet guide vane ring  24 A not typically being counted as a separate stage).  
         [0021]    [0021]FIG. 1A shows further details of the bleed port  38 . The port has an interior surface  50  which converges slightly from upstream to downstream near its upstream end at the surface  32 . The surface  50  extends radially outward therefrom as a generally right slot at a longitudinal angle θ to the axis  500 . The local wall inboard surface  32  may be somewhat off-longitudinal (e.g., converging slightly such as by up to about 1°) at this point. The surface  50  extends along a lip formed as tubular projection  54  radially outward and aft into the plenum  42  beyond a generally cylindrical local portion of the surface  34 . This projection or lip has an exterior/outer surface  56  and a downstream rim surface  58 . The exterior surface  56  is generally parallel to the interior surface  50  outboard of a root transition  60  along the lip&#39;s leading and trailing edge portions  62  and  64  and lateral portions  66 . In the exemplary embodiment, the transition  60  is sub-flush to the local cylindrical portion of the surface  34  defining a recess  70  circumscribing the lip  54 . The exemplary bleed port has a length L along the bleed flowpath  504 . In the exemplary embodiment, the leading and trailing edges of the bleed port inlet  80  and  81  are longitudinally radiused. The length may thus advantageously be measured from the projected intersection of the straight medial portions of the interior surface  50  along the leading edge wall or portion  62 . The interior of the rim surface  50  may be much more sharply radiused and the length may be measured to a similarly projected value (the projection difference creating a relatively insignificant difference). The length may alternatively be measured near the trailing edge of the port or in-between. As discussed below, performance is believed more sensitive to length along the leading edge and, therefore, this measurement location is contemplated unless otherwise noted. The exemplary bleed port is elongate in the circumferential direction about the axis  500 . Its smaller dimension is thus transverse to the flowpath  504  and has a depth D. The port height (e.g., of the rim  58  radially beyond the surface  32 ) is Lsinθ. Additional dimensions shown are the thickness T of the unrecessed portions of the wall  30  (e.g., between the cylindrical portions of the surfaces  32  and  34 ), the depth R of the recess  70  (e.g., of the nadir of the recess below the cylindrical portion of the surface  34 ), and the thickness S of the lip  54  away from its root and tip.  
         [0022]    In an exemplary embodiment, the ratio of L to D is chosen to be approximately 3.0 (e.g., 2.5-3.5 or, more narrowly, 2.8-3.2). Exemplary values of L and D are 0.88 and 0.29 inches. A broader range of L is 0.7-1.0 inch. An exemplary value of θ is 45.87°. An exemplary range of θ is 40°-50°. Narrower ranges are 43°-47° and 44°-46°. An exemplary lip wall thickness S is 0.080 inch. An exemplary range is 0.060-0.090 inch. A narrower range is 0.065-0.085 inch. An exemplary height H is 0.674 inch. An exemplary range is 0.60-0.75 inch. A narrower range is 0.65-0.70 inch. An exemplary case wall thickness T is 0.245 inch. An exemplary difference between H and T is at least 0.4 inch. A narrower difference range is at least 0.5 inch. An exemplary recess depth R is 0.06 inch. An exemplary range is 0.05-0.07 inch. An exemplary longitudinal radius of curvature at the leading edge of the inlet of the bleed port is 0.12 inch. An exemplary range is 0.09-0.25 inch. An exemplary radius of curvature at the downstream edge of the inlet port is 0.031 inch. An exemplary range is 0.024-0.063 inch. The depth and geometry of the recess are selected for weight reduction in view of strength considerations. To maintain strength, a transition  60  is curved, having a relatively tight radius of curvature along the trailing wall  64  and a greater radius of curvature along the leading wall  62 . The relative straightness of the port (especially of the downstream portion of the port near its rim) and the size/shape of the recess are artifacts of weight and manufacturability concerns. Ideally, to minimize flow disturbance and increase diffusion (and thereby minimize pressure losses through the bleed port) the port would diverge near its downstream end. Computationally, it appears that ratios of L to D approaching or exceeding 3:1 exhibit a high reduction in flow separation. Ratios substantially greater than 3:1 appear to provide little additional flow benefit to justify the weight penalty.  
         [0023]    A further reduction in weight may be obtained by further truncating the portion of the lip along the trailing edge or extreme of the bleed port so that the outlet is more nearly perpendicular to the bleed flow  504 . It appears that flow performance is not particularly sensitive to this shortening. FIG. 2 shows a bleed port  138  having an inlet  140  similarly dimensioned and positioned to the inlet of the embodiment of FIG. 1A. The outlet  141  defined by the rim  158  is perpendicular to the bleed flow. In the exemplary embodiment, the leading portion  162  of the lip is the same as that of FIG. 1A whereas the trailing portion  164  is relatively shortened and the lateral portions  166  more perpendicular (right) at their downstream ends.  
         [0024]    The lower sensitivity to shortening of the trailing portion of the lip appears to be not merely the case when it protrudes farther downstream than does the leading portion. Accordingly, FIG. 3 shows yet another port  238  where the lip trailing portion has been entirely removed so that the trailing portion of the port terminates at the recess  270  in the surface  234 . In this exemplary embodiment, the leading portion  262  is substantially the same as the leading portions of FIGS. 1A and 2, as is the inlet  240 . The outlet  241  is defined by the rim  258  along the leading portion  262 , side portions  266 , and along the recess  270  at the trailing edge of the port.  
         [0025]    [0025]FIG. 4 shows an exemplary prior art engine case segment  400  having an outboard wall segment  402  with inboard and outboard surfaces and a pair of compressor bleed ports  404  therebetween. The exemplary segment  400  has a pair of inboard wall segments  406  and  408  with groups of respective airfoils  410  and  412  extending between the such inboard wall segments and the outboard wall segment  402 . In the exemplary embodiment, the segment is dimensioned to nominally encompass 30° about the engine so that twelve such segments may be assembled side-to-side in a ring to provide twenty-four ports and encompass two stator stages of the engine. In an exemplary implementation, exemplary circumferential lengths (lengths along the circumference of the segment about the axis  500  at the port inlet of the ports are 2.0-2.3 inch. More narrowly, 2.1-2.2 inch. Multiple rings may be assembled end-to-end for the additional stages.  
         [0026]    The segment  400  of FIG. 4 may be removed from its engine and replaced with a replacement stator segment  440  (FIG. 5). An outboard wall  442  of the segment  440  provides a sector of the case wall  30  of FIG. 1. Inboard wall segments  446  and  448  are respectively connected to the outboard wall segment  442  by groups of the vanes  24 E and  24 F. The exemplary segment  400  may be formed such as by investment casting of nickel-based superalloy. The exemplary segment can be formed from two unitarily-cast subsegments joined along a circumferential weld  450  such as by electron beam welding. The exemplary weld is aft of the bleed ports dividing the outboard wall segment longitudinally approximately in half with the vanes  24 E and inboard wall segment  446  unitarily formed with the leading half and the vanes  24 F and inboard wall segment  448  unitarily formed with the trailing half.  
         [0027]    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, when implemented as a reengineering or retrofit of an existing compressor, details of the existing compressor may influence or dictate details of the implementation. Accordingly, other embodiments are within the scope of the following claims.