Abstract:
A turbine cooling component comprising a circumferential leading edge, a circumferential trailing edge, a pair of spaced and opposed side panels connected to the leading and trailing edges, an arcuate base connected to the trailing and leading edges having a fore portion, a midsection portion, an aft portion, opposed side portions, an outer surface partially defining a cavity operative to receive pressurized air, and an arcuate inner surface in contact with a gas flow path of a turbine engine, a first side cooling air passage in the base extending along the first side portion from the fore portion to the aft portion, and a fore cooling air passage in the fore portion of the base communicative with the side cooling air passage and the cavity, operative to receive the pressurized air from the cavity.

Description:
BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates to turbine engines and particularly to methods and apparatus involving shroud cooling in turbine engines. 
     The high pressure turbine section of a turbine engine includes rotor blades extending radially from a disk assembly mounted inside a casing. The turbine engine includes a shroud assembly mounted on the circumference of the casing surrounding the rotor blades. The rotor blades and shroud assembly are subjected to a high temperature gas flow that affects the rotation of the rotor blades. The rotor blades include a blade tip at a distal end of a rotor blade. A small gap is defined between the blade tips and the shroud assembly. The small gap is desirable for engine efficiency since gas flow passing through the gap does not efficiently affect the rotation of the rotor blades. 
     In practice, the shroud assembly often comprises a number of segments mounted to the casing to form a circumferential shroud assembly. The shroud assembly is subjected to high temperatures and the segments are often cooled with flowing pressurized air. The pressurized air contacts a surface of a shroud segment and may pass through internal passages of the shroud segment and into the gas flow path inside the casing. Once the pressurized air has cooled the shroud segment, the pressurized air entering the gas flow path may undesirably affect the gas flow path by changing a direction of flow. Thus, it is desirable to reduce the amount of pressurized air used to cool the shroud segment and to discharge the pressurized air into the gas flow path in a manner that lessens the effects to the gas flow path. 
     BRIEF DESCRIPTION OF THE INVENTION 
     According to one aspect of the invention, a turbine cooling component comprising, a circumferential leading edge, a circumferential trailing edge spaced from the leading edge, a first side panel connected to the leading and trailing edges, a second side panel connected to the leading and trailing edges, spaced and opposed to the first side panel, an arcuate base connected to the trailing ledge and the leading edge having a fore portion, a midsection portion, an aft portion, an opposed first side portion and second side portion, an outer surface partially defining a cavity operative to receive pressurized air, and an arcuate inner surface in contact with a gas flow path of a turbine engine moving in the direction from the leading edge to the trailing edge of the turbine component, a first side cooling air passage in the base extending along the first side portion from the fore portion to the aft portion, and a fore cooling air passage in the fore portion of the base communicative with the side cooling air passage and the cavity, operative to receive the pressurized air from the cavity. 
     According to another aspect of the invention, a method for manufacturing a turbine cooling component comprising, forming a first side cooling air passage in a base of a shroud segment having a circumferential leading edge, a circumferential trailing edge spaced from the leading edge, wherein the first side cooling air passage extends through the circumferential leading edge and the circumferential trailing edge, and forming a fore cooling air passage communicative with the first side cooling air passage, extending through a first side panel of the shroud segment connected to the leading and trailing edges and a second side panel connected to the leading and trailing edges, spaced and opposed to the first side panel. 
     According to yet another aspect of the invention, a method for forming a cooling air passage in a component comprising, forming a first portion of an air passage having a first inner diameter in the component with a probe, forming a second portion of the air passage having the first inner diameter in the component communicative with the first portion of the air passage with the probe, and varying a rate of travel of the probe such that the probe increases the inner diameter of the second portion of the air passage to a second inner diameter. 
     These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a side partially-cutaway view of a turbine cooling subassembly in the form of a shroud assembly. 
         FIG. 2  is at top partially cut away view of an exemplary embodiment of the shroud segment of  FIG. 1 . 
         FIG. 3  is at top partially cut away view of an alternate exemplary embodiment of the shroud segment of  FIG. 1 . 
         FIG. 4  is at top partially cut away view of another alternate exemplary embodiment of the shroud segment of  FIG. 1 . 
         FIG. 5  is at top partially cut away view of an exemplary method for manufacturing the shroud segment of  FIG. 1 . 
         FIG. 6  is at front partially cut away view along the line A-A of  FIG. 5 . 
         FIG. 7  is a top cut away view of a portion of an exemplary profiled inner surface of a passage. 
         FIG. 8  is a top cut away view of a portion of an exemplary method of forming the profiled inner surface of the passage of  FIG. 7 . 
     
    
    
     The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a side partially-cutaway view of a turbine cooling subassembly in the form of a shroud assembly generally indicated at  100  disposed in a surrounding relation with turbine blades  112 . The turbine blades  112  are connected to a rotor (not shown) in a high pressure turbine section of a turbine engine. The gas flow path is shown in the direction of the arrows  101 . The shroud cooling assembly  100  includes a shroud having an annular array of arcuate shroud segments. A shroud segment is shown generally at  102 . The shroud segments  102  are held in position by an annular array of arcuate hanger sections. A hanger section is shown generally at  104 . The hanger sections  104  are supported by an engine outer case shown generally at  106 . 
     The shroud segment  102  includes a base  108 , a fore rail  110  radially and forwardly extending from the base  108  that defines a circumferential leading edge of the shroud segment  102 , an aft rail  114  that defines a circumferential trailing edge of the shroud segment  102 , and angularly spaced side rails  116  radially outwardly extending from the base  108 . The base  108  partially defines a shroud segment cavity  118 . 
     In operation, pressurized air  103  from, for example, the compressor section of the turbine engine enters an upper plenum cavity  120  defined by the hanger section  104 , and enters the shroud segment cavity  118  via holes  122  in the hanger section  104 . The pressurized air  103  in the shroud segment cavity  118  impinges on a radially outer surface  124  of the base  108 . Impingement air  105  cools the base  108 , and enters entrance holes  130  of passages  126  that extend from the outer surface  124  of the base  108  into the base  108  to provide convection cooling of the shroud segment  102 . The impingement air  105  exits the passages  126  via exit holes  128  located in the aft rail  114  of the shroud segment  102 . Once the impingement air  105  has exited the exit holes  128 , the impingement air  105  enters the gas flow path shown by the arrow  101 . 
       FIG. 2  illustrates at top partially cut away view of an exemplary embodiment of the shroud segment  102 . The shroud segment  102  includes a fore passage  202  communicative with the shroud segment cavity  118  via the entrance holes  130 . The fore passage  202  is communicative with side passages  204  that include the exit holes  128 . In operation, impingement air  105  (of  FIG. 1 ) enters the entrance holes  130  and flows through the fore passage  202  and the side passages  204 , and exits into the gas flow path via the exit holes  128 . The illustrated embodiment includes supplemental pressure holes  206  that may be included to provide additional impingement air  105  to the side passages  204 . The supplemental pressure holes  206  compensate for a loss of impingement air  105  pressure in regions of the side passages  204  that are remote from the entrance holes  130 . 
     The location of the fore passage  202  and the side passages  204  increases convection cooling in the fore rail  110  and the side rail  116  regions of the shroud segment  102 . The fore rail  110  and the side rail  116  regions of the shroud segment  102  have been shown through experimentation to become relatively hotter than regions of the base  108  that are below to the shroud segment cavity  118  and are cooled by impingement air  105  that collects and cools the shroud segment cavity  118 . 
     Previous embodiments of shroud segments have included vent holes disposed along the side rails  116 , fore rail  110 , and aft rail  114  that receive impingement air  105  from the shroud segment cavity  118  and port the impingement air  105  along outer surfaces of the shroud segment cavity  118  into the gas flow path. The illustrated embodiment of  FIG. 2  uses the fore passage  202  and side passages  204  to cool the fore rail  114  and side rail  116  regions and may not include such vent holes. One advantage of omitting the vent holes is that the shroud segment  102  may include a thermal coating along the radially inner surface  132  (of  FIG. 1 ). In production, the coating may be applied after the vent holes are fabricated (cast or drilled into the shroud segment  102 ), or applied before the vent holes are fabricated. If the coating is applied after the vent holes are fabricated, the vent holes are covered to prevent the coating from fouling the vent holes. If the coating is applied before fabricating the vent holes, the coating is removed from the area of the vent holes prior to fabrication. Either of these production methods increases the production costs of the shroud segment  102 . 
     The increased cooling in the fore rail  114  and the side rail  116  provided by the location of the fore passage  202  and the side passages  204  may provide an opportunity to omit vent holes from the design of the shroud segment  102 , reducing production costs. Other benefits may include reducing the amount of impingement air  105  that exits the shroud segment  102 . The exiting impingement air  105  is often undesirable because the exiting impingement air  105  enters the high pressure section of the turbine engine and may negatively affect the gas flow path, thereby reducing the efficiency of the engine. The impingement air  105  is often ported from the air compressed in the compression section of the turbine engine (bleed air). Bleed air used for cooling is not used for combustion; thus reducing the bleed air used for cooling increases the efficiency of the turbine engine. 
     The illustrated embodiment of  FIG. 2  is not limited to include two entrance holes  103  and exit holes  128 , but may include any number of entrance holes  130  and exit holes  128 , including a single entrance hole  130  or a plurality of entrance holes  130 , and a single exit hole  128  or a plurality of exit holes  128 . 
       FIG. 3  illustrates an alternate exemplary embodiment of the shroud segment  102 . The shroud segment  102  in  FIG. 3  is similar to the shroud segment  102  of  FIG. 2  and includes an aft passage  208  communicative with the side passages  204 . The aft passage  208  routs impingement air  105  for convection cooling of the aft rail  114  region of the shroud segment  102 . 
       FIG. 4  illustrates another alternate exemplary embodiment of the shroud segment  102 . The shroud segment  102  in  FIG. 4  is similar to the shroud segment  102  of  FIG. 2  and includes a plurality of vent holes  210  communicative with the side passages  204  and the outer surface of the side rails  116 . The vent holes  210  may be used to increase the cooling of the outer surface of the side rails  116 , though the vent holes  210  may increase production costs. 
       FIG. 5  illustrates at top partially cut away view of an exemplary method for manufacturing the shroud segment  102 . The fore passage  202 , the side passages  204 , and the aft passage  208  have been formed through the outer surfaces of the fore rail  110 , the side rails  116 , and the aft rail  114 . Once the passages have been drilled the undesirable drill holes may be sealed in the regions  501 . The forming of the passages may be performed using a variety of techniques including, for example, drilling, electrical discharge machining (EDM), and electro chemical machining (ECM). 
       FIG. 6  illustrates at front partially cut away view along the line A-A (of  FIG. 5 ) of an exemplary method for manufacturing the shroud segment  102 . The radially inner surface  132  of the shroud segment  102  includes an annular profile. The annular profile may make drilling the fore passage  202  difficult. The drilling of the fore passage  202  may be more easily performed by drilling the fore passage  202  from each side rail  116  at an angle theta. For example, the drilling procedure may include drilling a first passage  601  from one of the side rails  116  at an angle theta to a mid point of the shroud segment  102 . A second passage  603  may then be drilled from the opposite side rail  116  at a similar angle with a drill depth that may intersect the first passage  601  approximately at the mid point of the shroud segment  102 . Alternate embodiments may include a first passage  601  and a second passage  603  that do not intersect. The drilling of the fore passage  202  at angles using from opposite side rails  116  accommodates the annular profile. The aft passage  208  (of  FIG. 5 ) may be drilled in a similar manner. The side passages  204  may be drilled in one drilling procedure if desired and will intersect portions of the fore passage  202  and the aft passage  208 . Once the passages have been drilled, the portions of the passages that translate through the outer surfaces of the shroud segment may be sealed. The desired entrance holes  130  and exit holes  128  may be drilled in subsequent processes. Though the methods for fabricating the passages described above include drilling, the passages in the shroud segment  102  may be fabricated using other methods including, for example, casting processes. 
     An advantage of using a (EDM/ECM) processes for fabricating the passages described above is that the drilling process may be used to create a profiled inner surface of the passages.  FIG. 7  illustrates a top, cut away view of a portion of an exemplary profiled inner surface of a passage. The profiled inner surface of the passage may be included as a feature of any of the passages described above, including the fore passage  202 , the aft passage  208 , and the side passage  204 . Referring to  FIG. 7 , a passage  701  includes ridges  705  that decrease the inner diameter of the passage  701 . The ridges  705  may improve the convective cooling of the impingement air  105  that flows in the passage  701 , by disrupting the flow of the impingement air  105  (of  FIG. 1 ). A desirable effect of the ridges  705  may include creating vortices in the flow of the impingement air  105  that increase the convective cooling effects of the impingement air  105 . 
       FIG. 8  illustrates an exemplary method for forming the ridges  705 . A EDM probe  801  is used to drill the passage  701 . While drilling, the probe  801  rotates, and is driven forward in the direction of the arrow  805  into the material  807  to drill the passage  701 . To form the ridges  705 , the forward drive of the probe  801  pauses momentarily while the probe  801  continues material removal in the region  803  increasing the inner diameter of the passage  701  in the region  803 . Pausing the forward drive of the probe  801  along portions of the passage  701  forms the ridges  705 . 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.