Abstract:
The present disclosure generally relates to variable cellular structures, methods of making such cellular structures, and variable cellular flow discouragers for turbine engines for jet aircraft.

Description:
INTRODUCTION 
       [0001]    The present disclosure generally relates to variable cellular structures, methods of making such cellular structures, and variable cellular flow discouragers for turbine engines for jet aircraft. 
       BACKGROUND 
       [0002]    Honeycomb cellular structures are known and widely used in the aviation industry. For example, U.S. Patent App. No. 2004/0048027 to Hayes et al. discloses a honeycomb core product for use in the leading edges and ailerons for aircraft wings and airfoils. The honeycomb core product is positioned on the leading edge of wing and is covered by an outer skin member and attached to a structural support member. U.S. Patent App. No. 2004/0048027 is hereby incorporated by reference herein in its entirety. 
         [0003]    Honeycomb structures have also been used as flow discouragers in gas turbine engines for jet aircrafts. For example, U.S. Patent App. No. 2012/0163955 to Devi et al. discloses a honeycomb-shaped flow discourager in a gas turbine.  FIG. 1  illustrates a perspective view of the interface between a rotor  10  and stator  12  in a gas turbine engine.  FIG. 2  illustrates a close up view of the interface shown  FIG. 1 , including a honeycomb-shaped flow discourager  14 . The stator  12  remains stationary relative to the rotor  10 , which turns due to the force of combustion gasses moving past the rotor vanes  16 . A portion of the combustion gas  18  leaks through the interface between the rotor tip  20  and the stator  12 , reducing the efficiency of the engine. To reduce leakage, a flow discourager  14  is placed at the interface between the stator  12  and the rotor tip  20  as shown in  FIG. 2 . The rotor tip  20  moves past a portion of the honeycomb structure  22  of the flow discourager  14  defining a rub path  24  as shown in  FIG. 3 . As shown in  FIGS. 2 and 3 , each of the honeycomb cells  22  have the same geometry including having the same relative wall thickness and contours. U.S. Patent App. No. 2012/0163955 is hereby incorporated by reference herein in its entirety. 
       SUMMARY 
       [0004]    The following presents a simplified summary of one or more aspects of the invention in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated aspects, and is intended to neither identify key or critical elements of all aspects nor delineate the scope of any or all aspects. Its purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later. 
         [0005]    The disclosure provides a cellular structure, comprising a thickness dimension defined by cell walls and a surface plane defined by the edges of interconnecting cells, the surface plane comprising a first cellular region of the cells having a first maximum dimension in the surface plane, the surface plane comprising a second cellular region of the cells having a second maximum dimension in the surface plane, wherein the second dimension is less than the first dimension, and the cell walls of at least one of the first or second cellular regions having a non-linear contour or variable thickness. 
         [0006]    In another aspect, the disclosure provides a turbine engine comprising a stator, a rotor, and an interface region between the stator and rotor and a flow discourager at the interface region. The flow discourage includes a cellular structure comprising a thickness dimension defined by cell walls and a surface plane defined by the edges of interconnecting cells, the surface plane comprising a first cellular region of the cells having a first maximum dimension in the surface plane, the surface plane comprising a second cellular region of the cells having a second maximum dimension in the surface plane, wherein the second dimension is less than the first dimension. 
         [0007]    These and other aspects of the invention will become more fully understood upon a review of the detailed description, which follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a side perspective view of the interface between a rotor tip and stator in a gas turbine engine. 
           [0009]      FIG. 2  is a close-up view of a conventional honeycomb-shaped flow discourager at the interface shown in  FIG. 1 . 
           [0010]      FIG. 3  is a top view conventional honeycomb flow discourager showing the rub path of the rotor tip. 
           [0011]      FIG. 4  is a top view of a schematic representation of a cellular structure of a flow discourager in accordance with aspects of the present invention. 
           [0012]      FIG. 5  is a top view of an alternate cellular structure of a flow discourager in accordance with aspects of the present invention. 
           [0013]      FIG. 6  is a cross sectional view of the first cell type shown in  FIG. 4 . 
           [0014]      FIG. 7  is a cross sectional view of the second cell type shown in  FIG. 4 . 
           [0015]      FIG. 8  is a cross sectional view of the third cell type shown in  FIG. 4 . 
           [0016]      FIG. 9  is schematic representation showing an example apparatus for additive manufacturing of the cellular structure of  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. 
         [0018]      FIG. 4  is a top view of a schematic representation of a cellular structure  400  that may be used as a flow discourager in a gas turbine engine. The cellular structure  400  comprises a plurality of cells having different geometries. The different cell geometries may define specific regions within the cellular structure  400 , such as the rub path  402  shown in  FIG. 4 . The cellular structure  400  includes a plurality of first cells  404  having a first geometry and a plurality of second cells  406  having a second geometry. The cellular structure  400  may also include a plurality of third cells  408  having a third geometry and these third cells may be provided within a transition between cells of the first and second types. 
         [0019]    Although the cells are depicted as spherical or elliptical, the geometry of each cell may vary as long as cells of different size are arranged as described herein. For example, the cells may be polygonal such as hexagons used in a honeycomb structure, but having different sizes so that the overall structure has different regions similar to as shown in 
         [0020]      FIG. 4 . For example,  FIG. 5  depicts a similar cellular structure as  FIG. 4  but using a combination of hexagonal, diamond, and triangular shapes. In this example, the maximum diameter of the cells in the in the interior flow path region are larger than the cells outside and on both sides of the flow path. Smaller cells are found in the transition region between cells outside and inside the flow path region.  FIG. 5  shows a plurality of cells having different geometries. The different cell geometries may define specific regions within the cellular structure  500 , such as the rub path  502 . The cellular structure  500  includes a plurality of first cells  502  having a first geometry and a plurality of second cells  504  having a second geometry. The cellular structure  500  may also include a plurality of third cells  506  having a third geometry and these third cells may be provided within a transition between cells of the first and second types or between cells the same type (e.g., between cells of the first type or between cells of the second type). The cellular structure may further include a plurality of cells  508  having a fourth geometry and these fourth cells may be provided within a transition between cells of the first, second, or third types or between cells the same type (e.g., between cells of the first type, between cells of the second type, or between cells of the third type). 
         [0021]    The term “dimension” as used in this application can mean any like-dimension measurement that can be used to compare the relative size of cells. For example, where the cells  406  are elliptical in shape, the dimension is preferably the maximum diameter  410  as shown in  FIG. 4 . In this case, the second cells  406  have a dimension (i.e., maximum diameter) that is larger than the same geometry of first cells  404  and the third cells  408 . In the case where all of the cells being compared are spherical (e.g., cells  404 ,  408 ), the diameter  412 ,  414  may be the geometry that is compared. For polygons (e.g., cells  502 ,  504 ,  506 ,  508 ), the geometry may be the maximum diameter but could also be a dimension of one of the portions of the polygon such as length of a side. 
         [0022]      FIG. 6  shows a cross section of first example cell  600 .  FIG. 7  shows a cross section a second example cell  700 .  FIG. 8  shows a cross section of a wall thickness of a third example cell  800 . As seen in  FIGS. 6-8 , each of the cells  600 ,  700 ,  800  comprises a thickness dimension  602 ,  702 ,  802 , which may be varied along the height  604 ,  704 ,  804  of the cell wall, e.g., the thickness is variable. Further, the cell wall may have a non-linear contour that may include one or more bends. For example, the cell  600  shown in  FIG. 6  has a thickness  602  that gradually decreases non-linearly toward the top edges  606  of the cell. In the cell  700 , shown in  FIG. 7 , the thickness  702  decreases nonlinearly toward the top edges  706  of the cell, but additionally includes a bend  708 . In the cell  800 , shown in  FIG. 8 , the thickness  802  decreases nonlinearly toward the top edges  806  of the cell, but additionally includes a plurality of bends  808  forming a zigzag pattern. While  FIGS. 6-8  show several example cell cross section profiles, other profiles may be implemented such as other thickness contours and other types and number of bends. For example, there may be less or more bends than as illustrated (e.g., the cell wall may include 1, 2, 3, 4, 5, 6, or more bends) and the sharpness (e.g., the angle) of the bends may be smaller or greater than illustrated. In one aspect of the present invention, the cell walls of the second plurality of cells  406  may have more bends than the cell walls of the first plurality of cells  404 . 
         [0023]    In an aspect of the present invention, any of the cell contours may be combined as neighboring cells in any variety of combinations. For example, cell  600  may be connected with cell  700  and/or  800 . Cell  700  may be connected with cell  600  and/or  800 . Multiple cells  600  (e.g., 2, 3, 4, 5, etc.) may be connected together followed by one or multiple (e.g., 2, 3, 4, 5, etc.) of cells  700  and/or cells  800 . Neighboring cells may alternate. 
         [0024]    The cellular structure  400  has a thickness dimension  604 , 704 ,  804  defined by the walls of the cells  600 ,  700 ,  800 . In an aspect of the present invention, the thickness dimension is uniform across the cellular structure, e.g., each of the thickness dimensions  604 ,  704 ,  804  is the same. In another aspect thickness dimensions  604 ,  704 ,  704  may vary. The cellular structure  400  includes a surface plane  416  defined by the edges  606 ,  706 ,  806  of interconnecting cells. The surface plane  416  comprises a first cellular region of the cells having a first maximum dimension  410  (e.g., the region having the second plurality of cells  406 ) in the surface plane  416 . The surface plane  416  comprises a second cellular region of the cells having a second maximum dimension  412  (e.g., the region having the first plurality of cells  404 ) in the surface plane  416 . As shown in  FIG. 4 , the second dimension  412  may be less than the first dimension  410 . The surface plane  416  may comprise a third cellular region of the cells having a third maximum dimension  414  (e.g., the region having the third plurality of cells  408 ) in the surface plane  416 . The third maximum dimension  414  may be smaller than both the first maximum dimension  410  and the second maximum dimension  412 . 
         [0025]    In an aspect of the present invention, the third plurality of cells  408  (e.g., the cells having the third maximum dimension  414 ) may define a transition region between the first and second regions. For example, as shown in  FIG. 4 , the third plurality of cells  408  are interspersed between the first plurality of cells  404  and the second plurality of cells  406 . By having the third plurality of cells  408  interspersed between the first plurality of cells  404  and second plurality of cells  406 , a smooth transition region is provided. As shown in  FIG. 4 , there may be two transition regions such that the center of the cellular structure (e.g., the rub path  402 ) is formed of the second plurality of cells  406 , with the center being surrounded by a transition region on opposing sides. As such, starting from one end of the cellular structure  400  and terminating on the opposing end (e.g., left side of the figure to the right side), the cell profile starts with the first plurality of cells  404 , followed by the third plurality of cells  408 , followed by the second plurality of cells  406 , followed by the third plurality of cells  408 , and terminating with the first plurality of cells  404 . 
         [0026]    In another aspect of the present invention, rather than having the third plurality of cells  408 , the transition region may comprise the first plurality of cells  404  and the second plurality of cells  406  being interspersed. For example, starting from one end of the cellular structure and terminating on the opposing end, the cell profile starts with the first plurality of cells  404 , followed by the first plurality of cells  404  and second plurality of cells  406  interspersed, followed by the second plurality of cells  406 , followed by the first plurality of cells  404  and second plurality of cells  406  interspersed, and terminating with the first plurality of cells  404 . The cellular structure may comprise a rub path  402  that interacts with the tip  20  of the rotor  10 . As shown in  FIG. 4 , the rub path  402  may include primarily (e.g., greater than 90% of the cells, preferably greater than 95% of the cells, preferably greater than 99% of the cells) the second plurality of cells  406 , and may also include some portion of the transition cells, e.g., the third plurality of cells  408 . As also seen in  FIG. 4 , outside of the rub path  402 , the cells are primarily (e.g., greater than 90% of the cells, preferably greater than 95% of the cells, preferably greater than 99% of the cells) the first plurality of cells  404  with some portion of the transition cells, e.g., the third plurality of cells  408 . In an aspect of the present invention, the second plurality of cells  406  may have a relatively higher radial stiffness as compared to the first plurality of cells  404 . This can be achieved by using cells configured with sufficient wall thickness and contour to achieve desired stiffness (e.g., cells  600 ,  700 ,  800 ). By primarily having cells with higher radial stiffness in rub path  402  and cells having lower radial stiffness outside the rub path  402 , the cellular structure  400  is optimized for performance when interacting with the tip  20  of the rotor  10 . 
         [0027]    Similarly, the cellular structure  500  has a thickness dimension defined by the walls of the cells  502 ,  504 ,  506 ,  508 . The cellular structure  500  includes a surface plane  510  defined by the edges of interconnecting cells. The surface plane  510  comprises a first cellular region of the cells having a first maximum dimension  512  (e.g., the region having the first plurality of cells  502 ) in the surface plane  510 . The surface plane  510  comprises a second cellular region of the cells having a second maximum dimension  514  (e.g., the region having the second plurality of cells  504 ) in the surface plane  510 . As shown in  FIG. 5 , the second dimension  514  may be less than the first dimension  512 . The surface plane  510  may comprise a third cellular region of the cells having a third maximum dimension  516  (e.g., the region having the third plurality of cells  506 ) in the surface plane  510 . The third maximum dimension  516  may be smaller than both the first maximum dimension  512  and the second maximum dimension  514 . The surface plane  510  may comprise a fourth cellular region of the cells having a fourth maximum dimension  518  (e.g., the region having the fourth plurality of cells  508 ) in the surface plane  510 . The fourth maximum dimension  518  may be smaller than all of the first maximum dimension  512  and the second maximum dimension  514 , and the third maximum dimension  516 . The cells of the cellular structure  500  may have the same wall structure as discussed herein with respect to the cellular structure  400 , such as having the same wall profiles shown in  FIGS. 6-8 . Additionally, as shown in  FIG. 5 , the second plurality of cells  504  (e.g., the cells having the second maximum dimension  514 ) and/or the third plurality of cells  506  (e.g., the cells having the third maximum dimension  516 ) and/or the fourth plurality of cells  508  (e.g., the cells having the fourth maximum dimension  518 ) may define a transition region between other regions. For example, as shown in  FIG. 5 , the third plurality of cells  506  may be located between the first plurality of cells  502  and the second plurality of cells  504 , while the second plurality of cells  504  and the fourth plurality of cells  508  may be located between the first plurality of cells  502 . By having the second plurality of cells  504 , the third plurality of cells  506 , and/or the fourth plurality of cells  508  between the first plurality of cells  502  and second plurality of cells  504 , a smooth transition region is provided. As shown in  FIG. 5 , there may be two transition regions such that the center of the cellular structure is formed of the first plurality of cells  502 , with the center being surrounded by a transition region on opposing sides. As such, starting from one end of the cellular structure  500  and terminating on the opposing end (e.g., left to right of the figure), the cell profile begins with the second plurality of cells  504 , followed by the third plurality of cells  506 , followed by the first plurality of cells  502 , followed by the second plurality of cells  504  and the fourth plurality of cells  508 , and terminating with the first plurality of cells  502 . 
         [0028]    The cellular structure described herein may be used in place of the honeycomb structure  14 ,  22  shown in  FIGS. 1 and 2 . For example, the gas turbine in accordance with aspects of the present invention may include all of the elements shown in  FIGS. 1 and 2 , including a stator, a rotor, and an interface region between the stator and rotor. 
         [0029]    The particular thickness and counters of the cell walls of a particular cell can be achieved through the use of additive manufacturing (AM) processes. AM processes generally involve the buildup of one or more materials to make a net or near net shape (NNS) object, in contrast to subtractive manufacturing methods. Though “additive manufacturing” is an industry standard term (ASTM F2792), AM encompasses various manufacturing and prototyping techniques known under a variety of names, including freeform fabrication, 3D printing, rapid prototyping/tooling, etc. AM techniques are capable of fabricating complex components from a wide variety of materials. Generally, a freestanding object can be fabricated from a computer aided design (CAD) model. A particular type of AM process uses an energy beam, for example, an electron beam or electromagnetic radiation such as a laser beam, to sinter or melt a powder material, creating a solid three-dimensional object in which particles of the powder material are bonded together. Different material systems, for example, engineering plastics, thermoplastic elastomers, metals, and ceramics are in use. Laser sintering or melting is a notable AM process for rapid fabrication of functional prototypes and tools. Applications include direct manufacturing of complex workpieces, patterns for investment casting, metal molds for injection molding and die casting, and molds and cores for sand casting. Fabrication of prototype objects to enhance communication and testing of concepts during the design cycle are other common usages of AM processes. 
         [0030]    Selective laser sintering, direct laser sintering, selective laser melting, and direct laser melting are common industry terms used to refer to producing three-dimensional (3D) objects by using a laser beam to sinter or melt a fine powder. For example, U.S. Pat. No. 4,863,538 and U.S. Pat. No. 5,460,758 describe conventional laser sintering techniques. More accurately, sintering entails fusing (agglomerating) particles of a powder at a temperature below the melting point of the powder material, whereas melting entails fully melting particles of a powder to form a solid homogeneous mass. The physical processes associated with laser sintering or laser melting include heat transfer to a powder material and then either sintering or melting the powder material. Although the laser sintering and melting processes can be applied to a broad range of powder materials, the scientific and technical aspects of the production route, for example, sintering or melting rate and the effects of processing parameters on the microstructural evolution during the layer manufacturing process have not been well understood. This method of fabrication is accompanied by multiple modes of heat, mass and momentum transfer, and chemical reactions that make the process very complex. 
         [0031]      FIG. 9  is schematic diagram showing a cross-sectional view of an exemplary conventional system  900  for direct metal laser sintering (DMLS) or direct metal laser melting (DMLM). The apparatus  900  builds objects, for example, the cellular structure  60 , in a layer-by-layer manner by sintering or melting a powder material (not shown) using an energy beam  936  generated by a source such as a laser  920 . The powder to be melted by the energy beam is supplied by reservoir  926  and spread evenly over a build plate  914  using a recoater arm  916  travelling in direction  934  to maintain the powder at a level  918  and remove excess powder material extending above the powder level  918  to waste container  928 . The energy beam  936  sinters or melts a cross sectional layer of the cellular structure under control of the galvo scanner  932 . The build plate  914  is lowered and another layer of powder is spread over the build plate and object being built, followed by successive melting/sintering of the powder by the laser  920 . The process is repeated until the cellular structure  400 , 500  is completely built up from the melted/sintered powder material. The laser  920  may be controlled by a computer system including a processor and a memory. The computer system may determine a scan pattern for each layer and control laser  920  to irradiate the powder material according to the scan pattern. After fabrication of the cellular structure  400 , 500  is complete, various post-processing procedures may be applied to the cellular structure  400 , 500 . Post processing procedures include removal of access powder by, for example, blowing or vacuuming. Other post processing procedures include a stress release process. Additionally, thermal and chemical post processing procedures can be used to finish the cellular structure  400 , 500 . 
         [0032]    The AM process may use any suitable material to form the cellular structures  400 ,  500 , and in particular materials useful for gas turbines. Example materials may be selected from the group consisting of steel, cobalt chromium, inconel, aluminum , and titanium. Thus, each cell of the formed cellular structure may comprise or consist of a material selected from the group consisting of steel, cobalt chromium, inconel, aluminum, and titanium. 
         [0033]    This written description uses examples to disclose the invention, including the preferred embodiments, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims. Aspects from the various embodiments described, as well as other known equivalents for each such aspect, can be mixed and matched by one of ordinary skill in the art to construct additional embodiments and techniques in accordance with principles of this application.