Abstract:
An internally-cooled turbomachine element has an airfoil extending between inboard and outboard ends. A cooling passageway is at least partially within the airfoil and has at least a first turn. Means are in the passageway for limiting a turning a loss of the first turn. The turbomachine element may result from a reengineering of an existing element configuration lacking such means.

Description:
U.S. GOVERNMENT RIGHTS 
   The invention was made with U.S. Government support under contract N00019-97-C-0050 awarded by the U.S. Navy. The U.S. Government has certain rights in the invention. 

   BACKGROUND OF THE INVENTION 
   The invention relates to the cooling of turbomachine components. More particularly, the invention relates to internal cooling of gas turbine engine blade and vane airfoils. 
   A well developed art exists regarding the cooling of gas turbine engine blades and vanes. During operation, especially those elements of the turbine section of the engine are subject to extreme heating. Accordingly, the airfoils of such elements typically include serpentine internal passageways. Exemplary passageways are shown in U.S. Pat. Nos. 5,511,309, 5,741,117, 5,931,638, 6,471,479, and 6,634,858 and U.S. patent application publication 2001/0018024A1. 
   Nevertheless, there remains room for improvement in the configuration of cooling passageways. 
   SUMMARY OF THE INVENTION 
   One aspect of the invention involves an internally-cooled turbomachine element comprising an airfoil extending between inboard and outboard ends. A cooling passageway is at least partially within the airfoil and has at least a first turn. Means in the passageway limit a turning loss of the first turn. 
   In various implementations, the means may comprise a wall essentially dividing the entirety of the first turn into first and second flowpath portions. A leading end of the wall may be upstream of the first turn (e.g., by at least 1.0 hydraulic diameters or, more narrowly, at least 1.5 hydraulic diameters, with an exemplary 1.5–2.5 or 1.5–2.0). The turn may be in excess of 90° or 120° and may be essentially 180°. The turn may be around an end of a wall. The element may have at least a first airfoil end feature selected from the group consisting of an inboard platform and an outboard shroud. The first turn may be at least partially within the first airfoil end feature. 
   Another aspect of the invention involves an internally-cooled turbomachine element having an airfoil extending between inboard and outboard ends. Internal surface portions define a cooling passageway at least partially within the airfoil. The cooling passageway has a first turn from a first leg to a second leg. A dividing wall bifurcates the cooling passageway into first and second portions and extends within the cooling passageway along a length from a wall first end to a wall second end. The first and second portions may each provide 25–75% of a cross-sectional area of the cooling passageway along said length of said wall, more narrowly, 35–65%. 
   The passageway may have a second turn from the second leg to a third leg. The wall first end may be proximate an end of the first leg at the first turn. The wall second end may be proximate an end of the third leg at the second turn. The wall first end may be 1.0–3.0 hydraulic diameters from the end of the first leg at the first turn. The wall second end may be 1.0–3.0 hydraulic diameters from the end of the third leg at the second turn. At the first turn, the passageway first portion may be within the second portion. At the second turn, the passageway second portion may be within the first portion. At the first turn, the passageway first portion may have a smaller cross-sectional area than the second portion. At the second turn, the passageway second portion may have a smaller cross-sectional area than the first portion. At the first turn, the passageway first portion may have a cross-section that is less wide than a cross-section of the second portion. At the second turn, the passageway second portion may have a cross-section that is less wide than a cross-section of the first portion. At the first turn, the passageway first portion may have a cross-section that is less elongate than a cross-section of the second portion. At the second turn, the passageway second portion may have a cross-section that is less elongate than a cross-section of the first portion. The element may be a vane having an inboard platform and an outboard shroud. The wall may have a number of apertures therein. The apertures may be no closer than an exemplary two hydraulic diameters from the first turn. 
   Another aspect of the invention involves a method for reengineering a configuration for an internally-cooled turbomachine element from a baseline configuration to a reengineered configuration. The baseline configuration has an internal passageway having first and second legs and a first turn therebetween. The method includes adding a wall to bifurcate the passageway into first and second portions. The wall extends within the passageway along a length from a wall first end to a wall second end. Otherwise, a basic shape of the first cooling passageway is essentially maintained. 
   In various implementations, the first cooling passageway may be slightly enlarged to at least partially compensate for a loss of cross-sectional area resulting from the addition of the wall. 
   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 partial, cut-away, partially-schematic, medial sectional view of a prior art airfoil. 
       FIG. 2  is a partial, cut-away, partially-schematic, medial sectional view of an inboard portion of an airfoil according to principles of the invention. 
       FIG. 3  is a partial, cutaway, partially schematic, medial sectional view of an outboard portion of an airfoil according to principles of the invention. 
       FIG. 4  is a partial sectional view of the airfoil of  FIG. 2 , taken along line  4 — 4 . 
       FIG. 5  is a partial sectional view of the airfoil of  FIG. 2 , taken along line  5 — 5 . 
       FIG. 6  is a sectional view of the airfoil of  FIGS. 2 and 3  at an intermediate location. 
       FIG. 7  is a sectional view of the airfoil of  FIG. 3 , taken along line  7 — 7 . 
       FIG. 8  is a partial sectional view of the airfoil of  FIG. 3 , taken along line  8 — 8 . 
     Like reference numbers and designations in the various drawings indicate like elements. 
   

   DETAILED DESCRIPTION 
     FIG. 1  shows a turbine element  40  shown as an exemplary vane having an inboard platform  42  and an outboard shroud  44 . An airfoil  46  extends from an inboard end at the platform to an outboard end at the shroud and has a leading edge (not shown) and a trailing edge  48  separating pressure and suction side surfaces. In the exemplary airfoil, one or more passageways of a cooling passageway network extend at least partially through the airfoil. In the exemplary airfoil, one passageway  50  extends in a downstream direction  500  along a cooling flowpath from an inlet  52  in the shroud to an exemplary closed downstream passageway end  54  which may be closed or may communicate with a port in the platform. 
   An upstream first leg  60  of the passageway  50  extends from an upstream end at the inlet  52  to a downstream end at a first turn  62  of essentially 180°. The first leg  60  is bounded by: an adjacent surface of a first portion  63  of a first wall  64 ; a first portion  65  of a second wall  66 ; and adjacent portions of passageway pressure and suction side surfaces (not discussed further regarding other portions of the passageway). The exemplary second wall  66  extends downstream to an end  67  at the first turn  62 . A second portion  68  of the first wall  64  extends along the periphery of the first turn  62 . A second passageway leg  70  extends downstream from a first end at the center of the first turn  62  to a second end at a second turn  72 . The second leg  70  is bounded by a continuation of the first surface of the wall  64  along a third portion  69  thereof and by an opposite second surface of the second wall  66 . The first wall  64  and its third portion  69  extend to an end  74  at the center of the second turn  72 . A second portion  75  of the second wall  66  extends along the periphery of the second turn  72 . 
   A third passageway leg  76  extends from a first end at the second turn  72  to a second end defined by the passageway end  54 . The third leg  76  is bounded by: a second surface of the first wall third portion  69  opposite the first surface thereof and extending downstream along the path  500  from the wall end  74 ; and a continuation of the second surface of the second wall  66  along a third portion  77  thereof. Along a portion of the third leg  76 , the exemplary second wall third portion  77  includes an array of impingement holes  80  extending into one or more impingement cavities or chambers  82 . An impingement cavity downstream wall  84  having apertures  85  separates the impingement cavities  82  from an outlet cavity  86 . An array of trailing edge cooling holes or slots  87  extend from the cavity  86  to the trailing edge. 
   In operation, a cooling airflow passes downstream along the flowpath  500  from the inlet  52  through the first leg  60  in a generally radially inboard direction relative to the engine centerline (not shown). The flow is turned outboard at the first turn  62  and proceeds outboard through the second leg  70  to the second turn  72  where it is turned inboard to pass through the third leg  76 . While passing through the third leg  76 , progressive amounts of the airflow are bled through the holes  80  into the impingement cavities  82 . From the impingement cavities  82 , the airflow passes out through the holes  85  into the outlet cavity  86 . From the outlet cavity  86 , the flow passes through holes/slots  87  to cool a trailing edge portion of the airfoil. 
   Viewed in cross-section transverse to the downstream direction, the exemplary passageway  50  is roughly transversely elongate rectangular (i.e., a radial span is substantially less than a height). In general, turning losses tend to increase with elongate passageway cross-sections (e.g., height much greater or less than radial span) and with sharper turns. Partially splitting the passageway into portions whose cross-sections (at least for one of the portions) are closer to square may reduce aerodynamic turning losses. In particular, an inboard portion may be made relatively less elongate than an outboard portion. The outboard portion may rely on a greater characteristic turn radius of curvature (e.g., mean or median) to maintain an advantageously low level of turning losses. 
     FIGS. 2 and 3  show a vane  140  which may be formed as a reengineered version of the vane  40  of  FIG. 1 . The exemplary reengineering preserves the general cooling passageway configuration (e.g., the shape and approximate positioning and dimensioning of the walls and other structural elements) but adds an exemplary single dividing wall  240  within the first passageway  150 . For ease of reference, elements analogous to those of the vane  40  are referenced with like reference numerals incremented by one hundred. The exemplary dividing wall  240  extends from a first end  242  ( FIG. 2 ) to a second end  244  ( FIG. 3 ) and has generally first and second surfaces  246  and  248 . The dividing wall  240  locally splits or bifurcates the passageway  150  into portions  150 A and  150 B and the flowpath  600  into first and second flow portions  600 A and  600 B. In the exemplary airfoil, this bifurcation starts near the downstream end of the first leg  160  and extends through the first turn  162 , second leg  170 , second turn  172 , to near the first (upstream) end of the third leg  176  where the flow portions fully rejoin. In the exemplary embodiment, the bifurcation and rejoinder advantageously occur within the respective first and third legs (as further discussed below), although they may alternatively occur within the first and second turns. 
   To preserve total cross-sectional area along the bifurcated flowpath, the walls defining the flowpath may be shifted slightly relative to the baseline airfoil of  FIG. 1 . For example, with a first portion  163  ( FIG. 2 ) of the first wall  164  fixed relative to its  FIG. 1  counterpart, the third portion  169  may be shifted somewhat toward the airfoil trailing edge. The third portion  177  of the second wall  166  may be similarly shifted relative to its counterpart (potentially shrinking the size of any impingement or outlet cavity or being associated with a switch from double impingement to single impingement if exterior airfoil shape and dimensions are essentially maintained). 
   The exemplary wall  240  has an approximately S-shaped planform with arcuate first and second turn portions  250  and  252  and a relatively straight leg  254  therebetween. Portions  250  and  252  are shown having diameters D 1  and D 2 , although they may be other than semicircular. Near the ends  242  and  244 , associated end portions  255  and  256  may be relatively straight and taper to provide smooth flow split and rejoinder and may extend by lengths L 1  and L 2  beyond the turns. 
     FIG. 6  shows the sections of the passageway portions  150 A and  150 B having characteristic heights H 1  and H 2  between interior pressure and suction side surfaces and characteristic widths W 1  and W 2  between adjacent walls. H 1  and H 2  and W 1  and W 2  may vary slightly around each turn. At the second turn, however, the relative transverse elongatedness of the two passageway portions is reversed. This permits whichever of the two portions is inboard at each of the turns to have a less elongate cross-section. 
   To achieve the switch between the first and second turns, the dividing wall  240  extends generally diagonally across the passageway second leg  170 . To equalize pressure across the wall  240  during this transition, the leg  254  has a row of apertures  260  along a central portion thereof. Advantageously, the upstream and downstream ends of the row are recessed from the upstream and downstream ends of the leg  170 .  FIGS. 2 and 3  show such recessing by lengths L 3  and L 4 . To minimize losses, advantageously, entering each turn, the dividing wall is continuous from upstream of such turn by a sufficient distance to provide desired flow through the turn, but not so far as to add unnecessary drag in the straight portion of the passageway leg thereahead. Advantageously, it may be continuous by at least one hydraulic diameter (of the inboard passageway portion at the adjacent end of the associated turn), more particularly, between about 1.5 and 2.0 hydraulic diameters. Accordingly, L 1  and L 4  may advantageously be of such dimension. Similarly, the wall may continuously extend downstream of the turn by a similar figure. Thus, L 2  and L 3  may be similar. Hydraulic diameter is defined as D H =4A/P, where A is the cross-sectional area and P is the wetted perimeter of the cross-section. 
   In the exemplary reengineering, the first turn  62  may have a turn loss parameter K T . The loss parameters for the outer and inner portions of the turn  162  (i.e., along first and second passageway portions  150 A and  150 B) may be substantially reduced, the loss along the outer portion being reduced by a greater factor due to the greater characteristic radius of curvature. For example, with an existing turn of loss parameter in the vicinity of 3.5–4, the reengineered turn may have an inboard portion of loss parameter in the vicinity of 2.0–2.5 and an outboard portion with loss parameter below 1.5, if not below 1.0. The second turn may see similar changes. 
   In other embodiments, the wall may be continuous between the two turns. In yet other embodiments, a wall may only extend through a single turn, although there may be individual walls for each of several turns. Depending on part geometry, the possibility exists of adding multiple walls for a given turn or turns. 
   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 to the reengineering of a variety of existing passageway configurations. Any such reengineering may be influenced by the existing configuration. Additionally, the principles may be applied to newly-engineered configurations. Accordingly, other embodiments are within the scope of the following claims.