Patent Publication Number: US-2005135923-A1

Title: Cooled vane cluster

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application discloses subject matter related to co-pending U.S. application “HOLE-DRILLING GUIDE AND METHOD” (APPLICANT REFERENCE NUMBER EH-10851). The disclosure of which is incorporated herein by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
      This invention was made with Government support under N00019-02-C-3003 awarded by the United States Navy. The Government has certain rights in this invention. 
    
    
     BACKGROUND OF THE INVENTION  
      (1) Field of the Invention  
      The invention relates to gas turbine engine components, and more particularly to a cast vane cluster with enhanced cooling.  
      (2) Description of the Related Art  
      A gas turbine engine includes a compressor for directing a primary fluid stream axially rearward, through a combustor and into a turbine. The turbine extracts power from a primary fluid stream and transmits the power through a shaft to rotate the forward-mounted compressor. A portion of the primary fluid stream is also directed to one or more secondary fluid streams for use in cooling components of the gas turbine engine. Disposed within the turbine section are alternating, annular stages of rotating blades and stationary vanes. The blades and vanes are disposed circumferentially about a central, longitudinal axis of the gas turbine engine.  
      Individual turbine vanes are comprised of an inner platform, an outer platform and an airfoil spanning radially outward from the inner platform to the outer platform. The airfoil contains a forward facing leading edge and a rearward facing trailing edge. The airfoil is staggered on the platforms in relation to the primary fluid stream direction, with the airfoil trailing edges of adjacent vanes forming an overlapping array. Together, the platforms and airfoils of adjacent vanes bound a duct for directing the primary fluid stream rearward. An inlet to the duct is bounded by adjacent airfoil leading edges and inner and outer endwall surfaces. An outlet to the duct is bounded by adjacent airfoil trailing edges and inner and outer endwall surfaces. The duct area generally converges in the axially rearward direction.  
      Vanes are typically investment cast of high-strength Nickel or Cobalt alloys and may contain multiple airfoils within a single casting. Vane castings with multiple airfoils are referred to as cast vane clusters and have the advantage of reducing the number of inter-platform interfaces in a turbine stage. Inter-platform interfaces are costly to manufacture and are a source of primary fluid stream leakage, which is detrimental to the operating efficiency of the gas turbine engine.  
      In cast vane clusters requiring cooling, one or more hollow passages extend through the interior of the airfoils forming a series of internal airfoil surfaces. The hollow passages direct a secondary fluid stream into the interior of the cast vane cluster. A multitude of cooling holes pass through the airfoil walls and into the hollow passages, allowing the secondary fluid stream to discharge into the primary fluid stream. Each hole comprises an inlet, an outlet and a bore extending from the inlet to the outlet along a central, longitudinal axis. Preferably, the multitude of cooling holes are drilled from the direction of the airfoil trailing edge and at an acute angle to the cast vane cluster surfaces. The drilling direction and angle are necessary to ensure that the secondary fluid stream is discharged in a substantially rearward direction. This optimizes the cooling effectiveness of the secondary fluid stream and reduces aerodynamic losses in the primary fluid stream.  
      Typically, cooling holes are drilled after a vane cluster casting is made. The standard methods used for drilling cooling holes in cast articles are laser and electrodischarge machining (EDM). Laser drilling methods utilize short pulses of a high-energy beam, an example is shown in U.S. Pat. No. 5,037,183. Electrodischarge machining (EDM) drilling methods pass an electrical charge through a gap between an electrode and a surface, an example is shown in U.S. Pat. No. 6,403,910. Both the laser and the EDM drilling methods require a line of sight from the drilling equipment to the hole location, limiting the surfaces that may be drilled.  
      Due to the stagger of the airfoils on the platforms of a cast vane cluster, portions of the duct surfaces are obstructed by the airfoil trailing edges and cannot be drilled using conventional laser or EDM drilling methods. The durability of cast vane clusters would be vastly improved if cooling holes could be placed wherever needed on the duct surfaces. What is needed is a cast vane cluster with cooling holes drilled into portions of the duct without a line of sight from the drilling equipment to the hole location.  
     BRIEF SUMMARY OF THE INVENTION  
      Provided is a cast vane cluster with cooling holes drilled into surfaces without a line of sight from the drilling equipment to the hole location.  
      In accordance with an exemplary embodiment, a cast vane cluster with enhanced cooling contains an inner and an outer platform and at least two airfoils for directing a primary fluid stream axially rearward. A duct is bounded by inner, an outer endwall surfaces, and adjacent airfoil fluid directing surfaces. The duct boundary contains at least one cooling hole for directing a secondary fluid stream to enhance cooling and extend the life of the cast vane cluster.  
      Other features and advantages will be apparent from the following more detailed descriptions, taken in conjunction with the accompanying drawings, which illustrate, by way of example, a preferred embodiment cast vane cluster with enhanced cooling. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       FIG. 1  is a simplified schematic of a gas turbine engine along a longitudinal axis.  
       FIG. 2  is an isometric view of a cast vane cluster of the type used in the gas turbine engine of  FIG. 1 .  
       FIG. 3  is a sectional top view of a cast vane cluster of  FIG. 2  showing an obstructed surface area.  
       FIG. 4  is an isometric view of an embodiment of a hole drilling guide for use in drilling holes into an obstructed surface area of a cast vane cluster.  
       FIG. 5  is an isometric view of an alternate embodiment of a hole drilling guide for use in drilling holes into an obstructed surface area of a cast vane cluster.  
       FIG. 6  is a sectional top view of a cast vane cluster of  FIG. 2  showing a hole-drilling guide of  FIG. 4  in place.  
       FIG. 7  is a sectional side view of a cast vane cluster of  FIG. 2  showing a hole-drilling guide of  FIG. 4  in place.  
       FIG. 8  is a sectional side view of a vane cluster of  FIG. 2  showing a hole-drilling guide of  FIG. 5  in place.  
       FIG. 9  is a partial sectional view of a cooling hole of a cast vane cluster of  FIG. 2 .  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      A gas turbine engine  10  with a central, longitudinal axis  12  is shown in  FIG. 1 . The gas turbine engine contains a compressor section  14 , a combustor section  16  and a turbine section  18 . A primary fluid stream  20  is directed axially rearward from the compressor section  14 , through the combustor section  16  and into the turbine section  18 . Within the compressor section  14 , a portion of the primary fluid stream  20  is directed to one or more secondary fluid streams  22 , which bypass the combustor section  16 , for use in cooling components within the gas turbine engine  10 . The turbine section  18  typically comprises multiple, alternating stages of rotating blades  24  and stationary vanes  26 . Multiple vanes may be cast as a single piece, which is typically called a cast vane cluster  32  (shown in  FIG. 2 ).  
      A cast vane cluster  32  comprises an inner platform  34 , an outer platform  36  and at least two airfoils  38  spanning radially outward from the inner platform  34  to the outer platform  36 . The inner platform  34  has an inner endwall surface  40  facing the airfoils and one or more inboard cavities  42  (shown in  FIGS. 7 and 8 ) opposite the airfoils. The outer platform  36  has an outer endwall surface  44  facing the airfoils and one or more outboard cavities  46  opposite the airfoils. As shown in  FIG. 3 , each of the airfoils  38  are comprised of a concave fluid directing surface  48 , a convex fluid directing surface  50 , a forward facing leading edge  52  and a rearward facing trailing edge  54 . Collectively, the platform endwall surfaces  40 ,  44  and airfoil fluid directing surfaces  48 ,  50  delineate a duct  56 , as shown in  FIG. 2 , for directing the primary fluid stream  20  rearward. One or more hollow passages  58  extend through the interior of the airfoils  38 , connecting the inboard  42  and outboard cavities  46 , (shown in  FIG. 8 ). In surfaces that have a line of sight from a drilling equipment direction  60 , a multitude of cooling holes  62  may be drilled using conventional laser or electrodischarge machining EDM drilling methods.  
      A typical cooling hole  62 , as shown in  FIG. 9 , is comprised of an inlet cross sectional area  65 , an outlet cross sectional area  66  and a bore  67 . The bore  67  extends through an airfoil wall  94 , from the inlet cross sectional area  65  to the outlet cross sectional area  66 , along a central, longitudinal axis  68 . Although this example shows a cooling hole  62  with circular inlet and outlet cross sectional areas  65 ,  66 , it is to be understood that any shape may be used. In addition, a cooling hole  62  may pass through an inner platform  34  or an outer platform  36  as well as an airfoil wall  94 .  
      Each of  FIGS. 6,7  and  8 , shows an exemplary embodiment cast vane cluster including one or more cooling holes  62  located in an obstructed area  64  (shown in  FIG. 3 ) of duct  56  (shown in  FIG. 2 ). Duct  56 , extends axially across portions of the platform endwall surfaces  40 ,  44 , and radially across portions of the airfoil fluid directing surfaces  48 ,  50 . One or more cooling holes  62 , located in portions of the duct  56 , may not be visible when viewed from an external location. Additionally, one or more cooling holes  62 , may only have an outlet cross sectional area  66  visible when viewed along a longitudinal axis  68  from an external location. An exemplary cast vane cluster, with enhanced cooling as described above, may be made using one or more of the hole-drilling guides and methods described below.  
       FIG. 4  shows an embodiment of a hole-drilling guide  70  for guiding a flexible, hole-drilling instrument  72  to a surface without a line of sight from the hole drilling equipment to a required hole location. The hole-drilling guide  70  comprises a body  74 , one or more inlet apertures  76 , one or more exit apertures  78  and a hollow, nonlinear raceway  80  connecting each corresponding inlet  76  and exit  78  apertures. Shown in this example are three raceways; however, any number may be used. An inlet aperture  76  may contain a conical, bell-shaped or a similar shaped entrance  82  to simplify insertion of the flexible, hole-drilling instrument  72 . The raceways  80  are a similar cross sectional shape as the flexible, hole-drilling instrument  72  and are slightly larger in sectional area. The clearance required between the flexible, hole-drilling instrument  72  and the nonlinear raceway  80  depends on the material of the hole-drilling guide  70  and the degree of curvature of the nonlinear raceway  80 . In this example, a radial clearance of approximately 0.004 inch is used. Each of the exit apertures  78  penetrates a substantially conforming face  84  of the hole-drilling guide  70 . The position of an exit aperture  78  in relation to an obstructed surface of an article is controlled by the substantially conforming faces  84 , and by other locating features such as rolls, pins, tabs, balls, bumps  86 . A clamping lug  88  allows the hole-drilling guide  70  to be rigidly secured to the article, once positioned.  
       FIG. 5  shows an alternate embodiment of a hole-drilling guide  70 . In the embodiment shown, the hole-drilling guide  70  comprises a body  74  and faces  84 , which substantially conform to an internal cavity or passage of an article. A clamping lug  88  allows the hole-drilling guide  70  to be rigidly secured to the article, once positioned, and contains one or more inlet apertures  76 . One or more exit apertures  78  penetrate the substantially corresponding surfaces  84  and are connected to the inlet apertures  76  by one or more nonlinear raceways  80 . Shown in this example are three nonlinear raceways; however, any number may be used.  
      In each of the above-described embodiments, the flexible, hole-drilling instrument  72  is an EDM electrode. The EDM electrode is formed of a flexible, electrically conductive wire with a diameter of between approximately (0.009-0.016) inches. For noncircular shaped holes, a flexible, electrically conductive foil strip of a comparable dimension may be used. The body  74  of the hole-drilling guide  70  is preferably made of an electrically insulating material using solid freeform fabrication, casting, molding, machining or any other suitable technique. Alternately, the body  74  may be formed of an electrically conductive material and the nonlinear raceways  80  may be coated with an electrically insulating material.  
      In one aspect of a hole-drilling method, shown in  FIG. 6 , a hole-drilling guide  70  is used to guide an EDM electrode  72  to a portion of an obstructed surface area  64  (shown in  FIG. 3 ) of a cast vane cluster  32 . In this example, the obstructed surface area is located on an airfoil convex fluid directing surface  50 . A cast vane cluster  32  is loaded in a single or multiple axis EDM station using a conventional tooling fixture  90 . In this example, an AMCHEM model HSD6-11, high-speed EDM station was used. A hole-drilling guide  70  is placed into a duct  56  (shown in  FIG. 2 ) of the cast vane cluster  32  and accurately positioned in relation to the cast vane cluster  32  by conforming surfaces  84  and a locating feature  86 . The hole-drilling guide  70  is rigidly secured by a clamp  92  contacting a clamping lug  88 . An EDM electrode  72  is inserted into an inlet aperture  76  and advanced along a nonlinear raceway  80 , until the electrode contacts the airfoil convex fluid directing surface  50 . Once loaded into the raceway  80 , the EDM electrode  72  is secured to the EDM station and plunged through an airfoil wall  94  into a hollow passage  58 , forming a hole  62 . Upon completion of the hole  62 , the EDM electrode  72  is retracted and the process is repeated as required.  
      In another aspect of a hole-drilling method, shown in  FIG. 7 , a hole-drilling guide  70  is used to guide an EDM electrode  72  to a portion of an obstructed surface area  64  (shown in  FIG. 3 ) of a cast vane cluster  32 . In this example, the obstructed surface area is located on an inner endwall surface  40 . A cast vane cluster  32  is loaded in a single or multiple axis EDM station using a conventional tooling fixture  90 . In this example an AMCHEM model HSD6-11, high-speed EDM station or equivalent may be used. A hole-drilling guide  70  is placed into a duct  56  (shown in  FIG. 2 ) of the cast vane cluster  32  and accurately positioned in relation to the cast vane cluster  32  by a conforming surface  84 . The hole-drilling guide  70  is rigidly secured by a clamp  92  contacting a clamping lug  88 . An EDM electrode  72  is inserted into an inlet aperture  76  and advanced along a nonlinear raceway  80 , until the electrode contacts the inner endwall surface  40 . Once loaded into the raceway  80 , the EDM electrode  72  is secured to the EDM station and plunged through an inner platform  34  into an inner cavity  42  of the vane cluster  32 , forming a hole  62 . Upon completion of the hole  62 , the EDM electrode  72  is retracted and the process is repeated as required.  
      In yet another aspect of a hole-drilling method, shown in  FIG. 8 , a hole-drilling guide  70  guides an EDM electrode  72  to a portion of an obstructed surface area  64  (shown in  FIG. 3 ) of a cast vane cluster  32 . In this example, the obstructed surface area is located on an airfoil concave fluid directing surface  48 , and is accessed via a hollow passage  58 . A cast vane cluster  32  is loaded in a single or multiple axis EDM station using a conventional tooling fixture  90 . In this example, an AMCHEM model HSD6-11, high-speed EDM station or equivalent may be used. A hole-drilling guide  70  is inserted into the hollow passage  58  of the vane cluster  32  and accurately positioned in relation to the hollow passage  58  by conforming surfaces  84  and locating features  86 . The hole-drilling guide  70  is rigidly secured by a clamp  92  contacting a clamping lug  88 . An EDM electrode  72  is inserted into an inlet aperture  76  and advanced along a nonlinear raceway  80 , until the electrode contacts the surface of the hollow passage  58 . Once loaded into the raceway  80 , the EDM electrode  72  is secured to the EDM station and plunged through the airfoil wall  94 , forming a hole  62  (not shown. Upon completion of the hole  62 , the EDM electrode  72  is retracted and the process is repeated as required.  
      The foregoing has described a cast vane cluster with enhanced cooling and its method of manufacture. 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 as described in the appended claims.