Patent Publication Number: US-11028703-B2

Title: Gas turbine engine airfoil with tip leading edge shelf discourager

Description:
BACKGROUND 
     The present disclosure relates to components for a gas turbine engine and, more particularly, to a tip shelf discourager of an airfoil. 
     Gas turbine engines typically include a compressor section to pressurize airflow, a combustor section to burn a hydrocarbon fuel in the presence of the pressurized air, and a turbine section to extract energy from the resultant combustion gases. Aviation applications include turbojet, turbofan, turboprop and turboshaft engines. Engine performance depends on precise control of the working fluid flow, including flow across the airfoil tip. Where clearance, abrasion and temperature effects are of concern, moreover, these factors often pose competing design demands on compressor and turbine rotor geometry, particularly in the tip region of the airfoil. 
     The tip region of some airfoils includes tip shelves to improve turbine airfoil durability by allowing cooling holes to be drilled or cast into the shelf which creates a cooling film over the shelf to effectively cool the blade tip region. CFD analysis of current configuration demonstrates that high pressure gas path flow pushes tip shelf cooling air over the airfoil tip prior to creating a film of cooling air on the tip shelf surface. Consequently, part durability is impacted due to cooling air not having time to cover the tip shelf surface. 
     SUMMARY 
     An airfoil for a gas turbine engine according to one disclosed non-limiting embodiment of the present disclosure includes a pressure sidewall and a suction sidewall extending to a tip region of the airfoil; a leading edge and a trailing edge defining a chord length of the airfoil therebetween; a tip shelf formed along the tip region of the airfoil between the pressure sidewall and a tip shelf wall; and a tip shelf discourager that extends from the tip shelf. 
     A further aspect of the present disclosure includes that the tip shelf discourager extends for a portion of a length of the tip shelf. 
     A further aspect of the present disclosure includes that the tip shelf discourager extends for an entire length of the tip shelf. 
     A further aspect of the present disclosure includes a squealer pocket formed within the tip region. 
     A further aspect of the present disclosure includes that the tip shelf wall is between the tip shelf discourager and the squealer pocket. 
     A further aspect of the present disclosure includes that the tip shelf discourager extends for a height equivalent to the tip shelf wall. 
     A further aspect of the present disclosure includes that the tip shelf discourager extends for a height less than the tip shelf wall. 
     A further aspect of the present disclosure includes that the squealer pocket is formed along a portion of the chord of the tip region. 
     A further aspect of the present disclosure includes that the squealer pocket extends from within 10% of the chord length measured from the leading edge to terminate less than 85% of the chord length measured from the trailing edge. 
     A further aspect of the present disclosure includes that the squealer pocket extends for more than 15% of the chord length and less than 75% of the chord length. 
     A further aspect of the present disclosure includes a plurality of cooling holes formed in the squealer pocket to maintain a pocket of cooling fluid along the tip region of the airfoil between the tip shelf wall and the squealer tip wall. 
     A further aspect of the present disclosure includes that the tip shelf discourager is about 0.01 inches in width. 
     A further aspect of the present disclosure includes that the tip shelf extends from the leading edge to an intersection of the pressure sidewall and the suction sidewall at the trailing edge such that the tip shelf communicates with both the pressure sidewall and the suction sidewall proximate to the trailing edge, wherein the tip shelf extends around the leading edge and onto the suction sidewall to terminate on the suction sidewall between the leading edge and the trailing edge of the airfoil. 
     A method of directing a cooling flow from an airfoil for a gas turbine engine, according to one disclosed non-limiting embodiment of the present disclosure includes discouraging a tip shelf cooling air from being mixed with core gas path air and pushed over a blade tip region. 
     A further aspect of the present disclosure includes directing a portion of the tip shelf cooling air along a length of a tip shelf discourager that extends from a tip shelf. 
     A further aspect of the present disclosure includes directing a portion of the tip shelf cooling air through cooling holes in a tip shelf discourager that extends from a tip shelf. 
     A further aspect of the present disclosure includes wherein the tip shelf extends from a leading edge to an intersection of a pressure sidewall and a suction sidewall at a trailing edge such that the tip shelf communicates with both the pressure sidewall and the suction sidewall proximate to the trailing edge, wherein the tip shelf extends around the leading edge and onto the suction sidewall to terminate on the suction sidewall between the leading edge and the trailing edge of the airfoil. 
     An airfoil for a gas turbine engine according to one disclosed non-limiting embodiment of the present disclosure includes a pressure sidewall and a suction sidewall extending to a tip region of the airfoil; a leading edge and a trailing edge defining a chord length of the airfoil therebetween; a tip shelf formed along the tip region of the airfoil between the pressure sidewall and a tip shelf wall; a tip shelf discourager that extends from the tip shelf, wherein the tip shelf extends from the leading edge to an intersection of the pressure sidewall and the suction sidewall at the trailing edge such that the tip shelf communicates with both the pressure sidewall and the suction sidewall proximate to the trailing edge, wherein the tip shelf extends around the leading edge and onto the suction sidewall to terminate on the suction sidewall between the leading edge and the trailing edge of the airfoil. 
     A further aspect of the present disclosure includes a squealer pocket formed within the tip region, the squealer pocket extends from within 10% of the chord length measured from the leading edge to terminate less than 85% of the chord length measured from the trailing edge. 
     A further aspect of the present disclosure includes that the squealer pocket extends for more than 15% of the chord length and less than 75% of the chord length. 
     The foregoing features and elements may be combined in various combinations without exclusivity, unless expressly indicated otherwise. These features and elements as well as the operation thereof will become more apparent in light of the following description and the accompanying drawings. It should be understood, however, the following description and drawings are intended to be exemplary in nature and non-limiting. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various features will become apparent to those skilled in the art from the following detailed description of the disclosed non-limiting embodiments. The drawings that accompany the detailed description can be briefly described as follows: 
         FIG. 1  is a schematic cross-section of an example gas turbine engine architecture; 
         FIG. 2  is an enlarged schematic cross-section of an engine turbine section; 
         FIG. 3  is a perspective view of an airfoil as an example component with a tip shelf discourager; 
         FIG. 4  is a schematic cross-section view of a tip region of  FIG. 3  showing the tip shelf discourager according to one disclosed non-limiting embodiment; 
         FIG. 5  is a schematic cross-section view of a tip region of  FIG. 3  showing the tip shelf discourager according to another disclosed non-limiting embodiment; 
         FIG. 6  is a perspective partial phantom view of the tip region; and 
         FIG. 7  is a schematic cross-section view of the tip region of  FIG. 6  showing the tip shelf discourager wall structure. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically illustrates a gas turbine engine  20 . The gas turbine engine  20  is disclosed herein as a two-spool turbo fan that generally incorporates a fan section  22 , a compressor section  24 , a combustor section  26  and a turbine section  28 . The fan section  22  drives air along a bypass flowpath while the compressor section  24  drives air along a core flowpath for compression and communication into the combustor section  26  then expansion through the turbine section  28 . Although depicted as a turbofan in the disclosed non-limiting embodiment, it should be appreciated that the concepts described herein may be applied to other types of engine architectures. 
     The engine  20  generally includes a low spool  30  and a high spool  32  mounted for rotation about an engine central longitudinal axis X relative to an engine static structure  36  via several bearing structures  38 . The low spool  30  generally includes an inner shaft  40  that interconnects a fan  42 , a low pressure compressor (“LPC”)  44  and a low pressure turbine (“LPT”)  46 . The inner shaft  40  drives the fan  42  directly or through a geared architecture  48  to drive the fan  42  at a lower speed than the low spool  30 . An exemplary reduction transmission is an epicyclic transmission, namely a planetary or star gear system. 
     The high spool  32  includes an outer shaft  50  that interconnects a high pressure compressor (“HPC”)  52  and high pressure turbine (“HPT”)  54 . A combustor  56  is arranged between the high pressure compressor  52  and the high pressure turbine  54 . The inner shaft  40  and the outer shaft  50  are concentric and rotate about the engine central longitudinal axis X which is collinear with their longitudinal axes. 
     Core airflow is compressed by the LPC  44  then the HPC  52 , mixed with the fuel and burned in the combustor  56 , then expanded over the HPT  54  and the LPT  46 . The turbines  54 ,  46  rotationally drive the respective low spool  30  and high spool  32  in response to the expansion. The main engine shafts  40 ,  50  are supported at a plurality of points by bearing structures  38  within the static structure  36 . 
     With reference to  FIG. 2 , an enlarged schematic view of a portion of the turbine section  28  is shown by way of example; however, other engine sections will also benefit herefrom. A full ring shroud assembly  60  within the engine case structure  36  supports a blade outer air seal (BOAS) assembly  62  with a multiple of circumferentially distributed blade outer air seals  64  proximate to a rotor assembly  66  (one schematically shown). 
     The full ring shroud assembly  60  and the BOAS assembly  62  are axially disposed between a forward stationary vane ring  68  and an aft stationary vane ring  70 . Each vane ring  68 ,  70  includes an array of vanes  72 ,  74  that extend between a respective inner vane platform  76 ,  78  and an outer vane platform  80 ,  82 . The outer vane platforms  80 ,  82  are attached to the engine case structure  36 . 
     The rotor assembly  66  includes an array of blades  84  circumferentially disposed around a disk  86 . Each blade  84  includes a root  88 , a platform  90  and an airfoil  92  (also shown in  FIG. 4 ). The blade roots  88  are received within a rim  94  of the disk  86  and the airfoils  92  extend radially outward such that a tip region  96  of each airfoil  92  is closest to the blade outer air seal (BOAS) assembly  62 . The platform  90  separates a gas path side inclusive of the airfoil  92  and a non-gas path side inclusive of the root  88 . 
     With reference to  FIG. 3 , the platform  90  generally separates the root  88  and the airfoil  92  to define an inner boundary of the core gas path. The airfoil  92  defines a blade chord between a leading edge  98  and a trailing edge  100  and defines a span height H from the platform  90  to the tip region  96 . A suction sidewall  102  that may be convex, and a pressure sidewall  104  that may be concave are joined at the leading edge  98  and at the axially spaced trailing edge  100 . The tip region  96  extends between the sidewalls  102 ,  104  opposite the platform  90 . It should be appreciated that the tip region  96  may include a recessed portion. 
     A tip shelf  110  and a squealer pocket  112  (also shown in  FIG. 4 ) are formed in the tip region  96  to provide improved tip cooling and resistance to oxidation, erosion and burn-through. The tip shelf  110  is located along the chord of the tip region  96 , extending axially from the leading edge  98  to the trailing edge  100  along the pressure sidewall  104 . A tip shelf discourager  130  extends from the tip shelf  110 . The tip shelf discourager  130  separates the tip shelf  110  from the pressure side gas path flow and essentially extends the span of the pressure sidewall  104  to form a discourager pocket  132  ( FIGS. 4 and 5 ) which is a closed radial recess in the tip region  96  adjacent to the squealer pocket  112 . The tip shelf discourager  130  provides an aerodynamic advantage as the tip shelf discourager  130  discourages cooling flow from mixing back into the core airflow. 
     A pressure side squealer tip wall  114  extends axially along tip region  96 , from leading edge  98  to trailing edge  100 . The pressure side squealer tip wall  114  is defined between the tip shelf  110  or discourager pocket  132  and the squealer pocket  112 , spaced from the pressure sidewall  104  by the discourager pocket  132 , and spaced from the suction sidewall  102  by squealer pocket  112 . 
     The squealer pocket  112  defines a closed perimeter radial recess in tip region  96 , between the pressure side squealer tip wall  114  and suction side squealer tip wall  116 . The suction side squealer tip wall  116  extends axially along the suction sidewall  102  of airfoil  92  at tip region  96 , from the leading edge  98  to the trailing edge  100 . The squealer pocket  112  retains cooling fluid (e.g., air) along the tip region  96  between the pressure sidewall  104  and the suction sidewall  102 . The discourager pocket  132  maintains a region or pocket of cooling fluid along the pressure sidewall  104 . 
     The tip shelf discourager  130  may extend for the entire chord of the airfoil from the leading edge  98  to the trailing edge  100  or for only a portion of the airfoil chord. The radial height of the tip shelf discourager  130  may be equivalent to the overall radial height of the airfoil  92  ( FIG. 4 ) or less ( FIG. 5 ) to define a clearance “W” with respect to the blade outer air seal  64 . The clearance “W” be greater than or equal to one quarter the distance between the tip shelf  110  and the pressure side squealer tip wall  114  and minimum of 0.020 inches (0.5 mm) in radial height. 
     The tip shelf discourager  130  may be parallel to the pressure side squealer tip wall  114  and transverse to the tip shelf  110 . In embodiments, the tip shelf discourager  130  may be at least from 0.010 inches (0.254 mm) (0.015 inches (0.381 mm) nominal with a profile tolerance of 0.010 inches (0.254 mm)). The width of the tip shelf  110  may be a minimum of 1.5× the width of the tip shelf discourager  130  to accommodate core printouts into the tip shelf  110 . 
     With reference to  FIG. 6 , the suction side squealer tip wall  116  is coextensive with the suction sidewall  102 , and spaced from the pressure side squealer tip wall  114  by the squealer pocket  112  in the mid-chord region B. Alternatively, the squealer pocket  112  may be segregated into multiple sections ( FIG. 7 ). The pressure side squealer tip wall  114  and the suction side squealer tip wall  116  may be of the same radial height and meet in the leading edge region A, along leading edge  98 , and in trailing edge region C, along trailing edge  100 . 
     In embodiments, the tip shelf  110  and the tip shelf discourager  130  extends along the tip region  96  for substantially all of the chord length L, including within the leading edge region A, (e.g., defined within 5-10% of chord length L from the leading edge  98 ), a mid-chord region B, (e.g., defined between 5-10% and 90-95% of the chord length L) and a trailing edge region C (e.g., defined within 5-10% of the chord length L from trailing edge  100 ). The tip shelf  110  and the tip shelf discourager  130  may thus extend more than 90%-95% of the chord length L between the leading edge  98  and the trailing edge  100 . In embodiments, the squealer pocket  112  extends from 75%-90% of the chord length L. The squealer pocket  112  may extend from within 5-10% of the chord length L from leading edge  98  in the leading edge region A, through the mid-chord region B to terminate in an aft region D from trailing edge  100  (e.g., defined between 10-25% of the chord length L). Thus, the tip shelf  110  and the tip shelf discourager  130  may be longer than squealer pocket  112  along chord L. This configuration facilitates a decrease in tip leakage over substantially the entire length of airfoil  92  along tip region  96 , improving rotor stage efficiency by reducing the tip loss penalty. 
     The combination of the tip shelf  110  and the squealer pocket  112  reduce the heat transfer coefficient across the tip region  96 , which reduces the net heat flux into the airfoil tip region  96  which may extend the performance and service life of the airfoil  92 . More specifically, the heat transfer coefficient may be substantially proportional to the Reynold&#39;s Number, which in turn may be substantially proportional to the mass flow. The structure of the tip shelf  110  and the squealer pocket  112  reduces mass flow, so the heat transfer coefficient is reduced in the tip region  96 . That is, there is less heat transfer from the hot core gas (working fluid) into the airfoil tip region  96  which results in in decreases thermal effects and improved service life for the airfoil  92 . 
     The airfoil  92  may also include internal cooling channels  118 . The internal cooling channels  118  provide cooling air into the discourager pocket  132  via tip shelf cooling holes  120 , and to the squealer pocket  112  via squealer tip cooling holes  122 . The tip shelf cooling holes  120  maintain a region of cooling fluid in the discourager pocket  132 , extending between the pressure side squealer tip wall  114  and the pressure sidewall  104 . The squealer tip cooling holes  122  maintain a region of cooling fluid in the squealer tip recess  108 . The discourager pocket  132  of cooling fluid provides a more uniform cooling temperature along the tip region  96  for better oxidation resistance, reduced erosion, and less burn-through. In embodiments, the tip shelf discourager  130  may include cooling apertures  134  to permit cooling flow from the tip shelf cooling holes  120  to flow through the tip shelf discourager  130 . 
     In some embodiments, the internal cooling channels  118  also provide additional cooling flow, for example, to trailing edge cooling slots  136 . In embodiments, the leading edge  98  is configured with indentation  138  to develop heat transfer and flow properties within an otherwise potential leading edge stagnation region. 
     The tip shelf  110  facilities cooling the tip region  96  as the cooling holes  120  along the tip shelf  110  direct cooling flow upward and over the tip region  96  to cool the tip region  96 . The tip shelf discourager  130  operates as a barrier between the tip shelf cooling flow from the tip shelf cooling holes  120  and the core gas path flow to discourage tip shelf cooling air from being mixed with core gas path air and pushed over the blade tip region and instead to be directed along the length of the tip shelf discourager  130 . This allows the cooling air to sit on the tip shelf  110  longer and thereby more effectively cool the blade tip region. This facilitates an improvement of the overall durability since the tip region is the thermally limited feature in most 1st stage HPT airfoils. The tip shelf discourager  130  also improves performance since tip clearances between the top of the ledge and the blade outer air seal  64  ( FIGS. 4 and 5 ) are reduced that between the surface of the tip shelf  110  and the blade outer air seal  64 . This decrease in tip clearance reduces leakage at and improves performance efficiency. 
     The use of the terms “a,” “an,” “the,” and similar references in the context of description (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or specifically contradicted by context. The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., it includes the degree of error associated with measurement of the particular quantity). All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other. It should be appreciated that relative positional terms such as “forward,” “aft,” “upper,” “lower,” “above,” “below,” and the like are with reference to normal operational attitude and should not be considered otherwise limiting. 
     Although the different non-limiting embodiments have specific illustrated components, the embodiments of this invention are not limited to those particular combinations. It is possible to use some of the components or features from any of the non-limiting embodiments in combination with features or components from any of the other non-limiting embodiments. 
     It should be appreciated that like reference numerals identify corresponding or similar elements throughout the several drawings. It should also be appreciated that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit herefrom. 
     Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present disclosure. 
     The foregoing description is exemplary rather than defined by the limitations within. Various non-limiting embodiments are disclosed herein, however, one of ordinary skill in the art would recognize that various modifications and variations in light of the above teachings will fall within the scope of the appended claims. It is therefore to be understood that within the scope of the appended claims, the disclosure may be practiced other than as specifically described. For that reason the appended claims should be studied to determine true scope and content.