Abstract:
A turbine casing ( 100 ) for a gas turbine, having a casing section ( 5   a,    5   b,    5   c,    5   d,    5   e ), the casing section ( 5   a,    5   b,    5   c,    5   d,    5   e ) having a containment section ( 16 ) for containing blade fragments expelled radially outward. The casing section ( 5   a,    5   b,    5   c,    5   d,    5   e ) has a first reinforcing element ( 1   a   , 1   b   , 1   c   , 1   d   , 1   e ) which is joined in face-to-face contact with the radially inner and/or outer surface of the casing section ( 5   a,    5   b,    5   c,    5   d,    5   e ).

Description:
[0001]    This claims the benefit of German Patent Application DE 10 2013 210 602.5, filed Jun. 7, 2013 and hereby incorporated by reference herein. 
         [0002]    The present invention relates to a turbine casing for a gas turbine having a casing section. 
       BACKGROUND 
       [0003]    Turbine casings for gas turbines are intended, inter alia, to ensure that, in the event of a mechanical rupture or breaking off of portions of a rotor blade, the resulting fragments cannot exit the turbine casing. Thus, the turbine casing is intended to prevent such fragments from damaging, for example, the wings or the fuselage of the aircraft. 
         [0004]    To ensure this, the so-called “containment requirement” was established, among other things, in the context of safety regulations. According to the containment requirement, all fragments of a turbine blade must be contained within the turbine casing, in particular in order to prevent other parts of the aircraft from being damaged by such fragments. 
       SUMMARY OF THE INVENTION 
       [0005]    It is an object of the present invention to provide a turbine casing for a gas turbine having a containment section. 
         [0006]    Thus, in accordance with the present invention, there is proposed a turbine casing for a gas turbine that has a casing section, in particular a low pressure turbine casing section, hereinafter abbreviated as LPT casing section. The LPT casing section is that part or section of the casing which covers or encloses the low pressure portion of the turbine with respect to the exterior of the turbine. 
         [0007]    The casing section has a containment section. The casing section may have or include more than one containment section. The containment section may be referred to as containment structure. The function of the containment section is to contain blade fragments which may become detached from the rotor blades and be expelled radially outward (i.e., in the direction of the centrifugal force) in the event of damage. Blade fragments which become detached from the rotor blades in the event of damage may be referred to as blade debris. 
         [0008]    The casing section of the turbine casing of the present invention has a first reinforcing element, which is joined in face-to-face contact with the inner and/or outer surface of the casing section, as viewed in a radial direction (“as viewed in a radial direction” will be abbreviated as “radial” hereafter). The casing section may have or include further reinforcing elements. 
         [0009]    In all of the above and following discussion, the expressions “may be” and “may have”, etc., will be understood to be synonymous with “is preferably” and “preferably has”, etc., and are intended to illustrate specific embodiments according to the present invention. 
         [0010]    Whenever number words are mentioned herein, these will be understood by those skilled in the art as an indication of a lower numerical limit. Therefore, for example, when “one” is specified, those skilled in the art will always read this to imply “at least one”, unless this would constitute a contradiction recognizable by those skilled in the art. This understanding is included in the present invention, as well as the interpretation that a number word such as “one” may alternatively be meant to mean “exactly one” whenever this is recognizable as technically possible by those skilled in the art. Both of these cases are covered by the present invention and apply to all number words used herein. 
         [0011]    Advantageous refinements of the present invention are the subject matter of the respective dependent claims and specific embodiments. 
         [0012]    Specific embodiments of the present invention may include one or more of the features mentioned below. 
         [0013]    The term “containment structure”, as used herein, refers to a containment casing, as used here in the field of gas turbines, in particular in aviation applications. The term “containment” is used in the context of safety regulations. In the event that, for any reason, a turbine blade or a portion thereof becomes detached from the rotor of a turbine, a containment structure is intended to ensure that all fragments are contained in the casing, and more specifically, in the turbine casing. This is also referred to as “containment requirement”. The containment requirement may have the consequence that the wall of the casing must be dimensioned such that it satisfies the requirement described above. The turbine casing encloses the rotor in order, inter alia, to prevent the fragments from damaging other parts or causing secondary damage. For example, damage may occur to the aircraft itself such as, for example, to the wings or to the fuselage, or fragments may get on the take-off or landing runway and cause damage to following aircraft. 
         [0014]    A containment structure may have one or more containment sections. 
         [0015]    In several embodiments of the present invention, the turbine casing, in particular the LPT portion thereof, may have a multi-shell or multi-layer design. This design enables a reduction in the overall wall thickness of the casing portion, thereby advantageously reducing weight, while at the same time satisfying the containment requirement. In other words, the casing portion is designed as a containment portion of multi-shell construction. Instead of a multi-shell construction (e.g., complete shells in the circumferential direction), multi-part containment rings (e.g., formed of multiple parts in the direction of the x-axis or axis of rotation) may also be used for the LPT casing portion. 
         [0016]    The term “containment of blade fragments or debris expelled radially outward”, as used herein, refers to the containment of such fragments within the turbine casing of the present invention. Due to the containment, blade fragments or debris that may be expelled radially outward can be prevented from exiting the turbine casing of the present invention. 
         [0017]    In some embodiments of the present invention, the gas turbine includes, inter alia, all the airfoils, in particular rotor blades, that are disposed in the low-pressure turbine. However, the low pressure turbine section may also include only one or several rotor blades, for example, without the stator vanes. 
         [0018]    In some embodiments of the present invention, the term “surface of the casing section”, as used herein, refers to any surface of the casing section that is suitable and/or intended for joining with a reinforcing element. A surface may be accessible when the casing section is in either an assembled or partially assembled condition. The surface may, for example, be an undercut or be accessible only after removing further sections of the casing section or parts attached thereto. 
         [0019]    In several embodiments of the present invention, a radially inner surface is one that is located within the casing section, and thus, is located in the radially inner area of the casing section as viewed from the centerline or axis of rotation of the turbine. Accordingly, a surface on the outside of the casing section may be referred to as a radially outer surface. 
         [0020]    In some embodiments of the present invention, at least one second reinforcing element is joined face-to-face with the first reinforcing element. The two reinforcing elements may be joined completely or partially such as, for example, in overlapping fashion. The first reinforcing element may be the one that is located radially further inwardly, and the second reinforcing element may be the one that is located radially further outwardly. 
         [0021]    In certain embodiments according to the present invention, at least one second reinforcing element is joined face-to-face with the first reinforcing element and face-to-face with the radially inner and/or outer surface of the casing section. For example, both reinforcing elements may be partially (e.g., in some areas) joined together face-to-face with the surface or surfaces (radially inner and/or outer surface) of the casing section (e.g., also in some areas). 
         [0022]    In several embodiments of the present invention, some or all of the reinforcing elements are strip-shaped, band-shaped, ring-shaped or partially ring-shaped, or lamellar in shape. 
         [0023]    In certain embodiments, the reinforcing elements are designed as shells or in the shape of shells. 
         [0024]    In some embodiments of the present invention, the reinforcing elements are reversibly or non-reversibly bendable, resilient, stiff, rigid, coated or uncoated. 
         [0025]    In certain embodiments of the present invention, the reinforcing elements are made from a metallic material, from a plastic material, or from a composite material, or may contain such a (composite) material. 
         [0026]    In some embodiments of the present invention, the at least two reinforcing elements are completely or partially in face-to-face contact with the radially inner and/or outer surface of the casing section. The reinforcing elements may, for example, be joined to only the inside or only the outside of the casing section. Furthermore, some or all of the reinforcing elements may be joined partially to the inside and partially to the outside of the casing section. For example, one or more reinforcing elements may be disposed on the outside, and one or more reinforcing elements may be disposed on the inside. Some of all of the reinforcing elements may be joined face-to-face with the surface of the casing section in a shell-like or layer-like manner. 
         [0027]    In several embodiments of the present invention, some or all of the reinforcing elements are ring-shaped. The reference axis is the axis of rotation of the gas turbine. The ring-shaped design in the circumferential direction may be rectangular, square, oval, round or differently shaped in cross-sectional area. 
         [0028]    In some embodiments of the present invention, the radius (mean radius relative to the centerline of the cross section in the circumferential direction) of ring-shaped reinforcing elements may be constant or variable in the axial direction (reference axis). Reinforcing elements may, for example, have different profiles in order, for example, to conform to the inner and/or outer surface of the casing section. 
         [0029]    In certain embodiments of the present invention, the characteristic parameter AN 2  of the low-pressure turbine in the low pressure turbine section has a value greater than 8000 (m/s) 2 . This value may be given in the units “inches” and “minutes” as approximately 4.45×10 10  (inch/min) 2 . Characteristic parameter AN 2  (synonymous with A*N 2 ) is the product of the cross-sectional area A of the gas duct in the gas turbine and the square of the maximum permissible speed N of the gas turbine. The characteristic parameter AN 2  is measured in particular at the last stage of the low-pressure turbine (in the direction of flow). The characteristic parameter AN 2  may be regarded as a measure of the centrifugal load on a blade. 
         [0030]    In several embodiments of the present invention, the reinforcing elements have a wound band or are made of a wound band. The band may be wound in several layers (in a radial direction). 
         [0031]    In some embodiments of the present invention, a wound band is one having a plurality of layers stacked in mutual face-to-face contact, the layers belonging to one and the same band. In order to create individual layers, the band is bent or folded. The band may also include a plurality of bands that are wound together. 
         [0032]    In certain embodiments of the present invention, the wound band is a metal band and/or a fabric band. For example, a metal band and a fabric band may be placed face-to-face one upon the other and subsequently wound. 
         [0033]    In some embodiments of the present invention, the reinforcing elements have one or more wire layers or are made of wire layers. The wire layers may be embodied as a braided wire mesh. 
         [0034]    In certain embodiments of the present invention, the reinforcing elements are arranged relative to one another such that they are stacked one on top of the other in a radial direction. The reinforcing elements may be stacked completely or partially one upon another, which means that the reinforcing elements cover each other completely or only partially. 
         [0035]    In several embodiments of the present invention, the reinforcing elements are fixed with one another and/or with the casing section by interlocking fit. The reinforcing elements may be fixed relative to one another, in particular in the axial direction, by interlocking fit. The reinforcing elements fixed relative to each other in this manner, or individual reinforcing elements, may likewise be fixed relative to casing section in the axial direction. 
         [0036]    In certain embodiments of the present invention, reinforcing elements in the form of wire layers are used for fixation relative to one another or for fixation relative to the casing section by means of free ends of individual wires of the wire layers. Such fixations may be used, for example, for axial securement. 
         [0037]    In some embodiments of the present invention, the reinforcing elements are fixed with one another and/or with the casing section by means of spot and/or tack welding. In particular for axial fixation, the reinforcing elements may be fixed relative to one another, individually with the casing section, or the reinforcing elements initially fixed relative to one another may be fixed with the casing section. 
         [0038]    In certain embodiments of the present invention, one or more turbine casing components is/are configured to be joinable or joined with the turbine casing by means of the reinforcing elements. The turbine casing components may be attached directly to the turbine casing by means of the reinforcing elements. Such turbine casing components may be, for example, holders for abradable liners, which are provided for attachment on the casing, flanges for additional turbine casing components, or the like. 
         [0039]    Some or all of the embodiments of the present invention may have one, several or all of the advantages mentioned above and/or hereinafter. 
         [0040]    By using reinforcing elements according to the present invention in the turbine casing of the present invention, the containment requirement can be achieved more easily than with other alternative structural designs. This is based on the following consideration of the damage mechanism, which changes with increasing energy of a potential fragment in the event of a mechanical (in the sense of separating) rupture or breaking off of portions of a rotor blade. In containment walls of turbines, the damage mechanism changes with increasing energy of the potential blade fragment due to the component stiffness, and thus an increased wall thickness requirement of the containment structure, the change being from buckling (plastic deformation) and subsequent tearing open under predominantly tensile stress in the case of lower energies and thin wall thicknesses to shear stress in the case of higher energies and thick walls. As a result of this change in loading, the containment capability decreases with increasing wall thickness of the containment structure. 
         [0041]    By using reinforcing elements according to the present invention in the turbine casing of the present invention, the containment requirement can advantageously be achieved more easily because the shear stress in the above-described damage mechanisms can be better accommodated or absorbed by the inventive reinforcing elements joined in face-to-face contact with the radially inner and/or outer surface of the casing section than by the heretofore customary containment systems according to the prior art. 
         [0042]    The at least one reinforcing element, which in certain embodiments is also referred to as shell, may preferably be fixed or mounted at no distance, or only a little distance, from the casing wall in order that, in a containment event (i.e., when, for example, a fragment of a rotor blade is hurled radially into the containment structure), mutual support is achieved against shear forces, and that, during further absorption of the fragment in the containment structure, frictional effects between the reinforcing elements are advantageously used to dissipate energy. 
         [0043]    When using the inventive turbine casing and the inventive connecting elements, the containment requirement may advantageously be distributed over several areas (reinforcing elements, additional shells, casing wall, etc.). By distributing the containment requirement over several shells, it is advantageously achieved that in the event of damage (containment event), initially mainly tensile stress is exerted on the shells (plastic deformation). In the case of further loading, the stress limit of the shell material may be exceeded, resulting in the formation of cracks in one or more shells, and even in the shells tearing completely open. Using the system of the present invention, where the reinforcing elements are joined in face-to-face contact with the radially inner and/or outer surface of the casing section, cracks occurring, for example, on the inner shell are advantageously stopped at the shell boundary, thereby preventing the excess tension caused a by crack from leading to rapid failure of the entire wall. All in all, these effects result in an advantageous reduction in the added wall thickness, and thus in weight. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0044]    The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which identical or similar components are indicated by the same reference numerals. The figures are simplified schematic views in which: 
           [0045]      FIG. 1  is a cross-sectional view of a portion of a turbine casing according to the presenting invention having reinforcing elements; 
           [0046]      FIG. 2  is a cross-sectional view of a portion of another turbine casing according to the presenting invention having reinforcing elements on the exterior side of a casing section; 
           [0047]      FIG. 3  is a cross-sectional view of a portion of yet another turbine casing according to the presenting invention having reinforcing elements on two casing sections; and 
           [0048]      FIG. 4  is a cross-sectional view of a portion of a further turbine casing according to the presenting invention having a reinforcing element in the form of a wound band. 
       
    
    
     DETAILED DESCRIPTION 
       [0049]      FIG. 1  shows, in simplified, schematic cross-sectional view, a portion of a turbine casing  100  according to the present invention having a first reinforcing element  1   a  and a second reinforcing element  1   a ′. First reinforcing element  1   a  is disposed on an interior side  3  of a low pressure turbine casing section  5   a  (abbreviated as LPT casing section  5   a ). Second reinforcing element  1   a ′ is disposed on first reinforcing element  1   a  face-to-face therewith. 
         [0050]    LPT casing section  5   a  has a containment section  16 . The two reinforcing elements  1   a  and  1   a ′ and the portion of LPT casing section  5   a  that is joined with first reinforcing element  1   a  are disposed within a containment section  16 . 
         [0051]    Flow through the gas turbine is in the x-direction. This is indicated by the arrow of flow direction  4 . 
         [0052]    The two reinforcing elements  1   a  and  1   a ′ are arranged face-to-face one above the other on the one hand, and, on the other hand, first reinforcing element  1   a  is fixed face-to-face on interior side  3  of LPT casing section  5   a . In this exemplary embodiment, reinforcing elements  1   a ,  1   a ′ are arranged annularly about the axis of rotation of the turbine (x-direction), so that the reinforcing elements  1   a ,  1   a ′ shown in cross section extend around the entire circumference of the turbine casing on interior side  3 . 
         [0053]    Reinforcing elements  1   a ,  1   a ′, as well as the portion of LPT casing section  5   a  that is joined face-to-face with second first reinforcing element  1   a ′, may be referred to as shells, shell elements or shell-shaped. 
         [0054]    In the example shown here, reinforcing elements  1   a ,  1   a ′ are arranged rotationally symmetric about the axis of rotation of the turbine. 
         [0055]    Alternatively, second reinforcing element  1   a ′ may be disposed on the exterior side of LPT casing section  5   a.    
         [0056]    The enlarged detail A shows a bore  6  in the form of a blind hole extending in radial direction y and having a bore diameter  8 . By means of this bore  6 , the two reinforcing elements  1   a ,  1   a ′ are fixed in the axial x-direction. Reinforcing elements  1   a ,  1   a ′ are curved at the point where they extend into bore  6 . This end region  7  may be obtained, for example, by plastic deformation when reinforcing elements  1   a ,  1   a ′ are in the mounted condition in casing section  5   a . By means of this axial fixation, reinforcing elements  1   a ,  1   a ′ can be prevented from being (axially) displaced. 
         [0057]    A rotationally symmetric abradable liner system  9  is fixed to another casing part  11 , which is located radially further inward with respect to LPT casing section  5   a  (i.e., further in the negative y-direction). This casing part  11  is fixed radially and axially by another, axially adjacent casing part  13  and a fixing element  15 . Casing part  11 , the axially adjacent further casing part  13 , as well as fixing element  15  are not hatched (i.e., not shown in cross section) in the cross-sectional view, but may also be ring-shaped or shell-shaped. 
         [0058]    LPT casing section  5   a  may be joined by a bolted connection  17  to further casing parts (not shown here) in a flange-like manner. 
         [0059]      FIG. 2  shows, in simplified, schematic cross-sectional view, a portion of another turbine casing  100  according to the present invention having a first reinforcing element  1   b , a second reinforcing element  1   b ′, and a third reinforcing element  1   b ″, which are disposed on exterior side  19  of an LPT casing section  5   b.    
         [0060]    Alternatively, additional reinforcing elements may be disposed on the interior side or on exterior side  19  of LPT casing section  5   b.    
         [0061]    The three reinforcing elements  1   b ,  1   b ′,  1   b ″ are arranged face-to-face one above the other. First reinforcing element  1   b  is fixed face-to-face on exterior side  19  of LPT casing section  5   b.    
         [0062]    The axial fixation of reinforcing element  1   b  against displacement in a direction opposite to axial direction X is achieved or assisted by curved ends  7  of reinforcing elements  1   b ,  1   b ′,  1   b ″ (in  FIG. 2  at the left end of reinforcing elements  1   b ,  1   b ′,  1   b ″). This is clearly shown in the enlarged detail B. In the example of  FIG. 2 , curved ends  7  abut a shoulder  21  of the surface geometry of LPT casing section  5   b  in a form-locking manner. The axial fixation of reinforcing elements  1   b ,  1   b ′,  1   b ″ against displacement in axial direction X is achieved or assisted directly by the geometry of LPT casing section  5   a  (in  FIG. 2  at the right end of reinforcing elements  1   b ,  1   b ′,  1   b ″). 
         [0063]    A rotationally symmetric abradable liner system  9  is fixed to another casing part  11 , which is located radially further inward with respect to LPT casing section  5   b . Casing part  11  is fixed radially and axially by another, axially adjacent casing part  13  on one side, by another casing part  13 ′ on the axially opposite side, and by a fixing element  15 . 
         [0064]    Reinforcing elements  1   b ,  1   b ′,  1   b ′, as well as the portion of LPT casing section  5   a  that is joined with first reinforcing element  1   b , are parts or sections of the containment structure or of containment portion  16 . 
         [0065]      FIG. 3  shows, in simplified, schematic cross-sectional view, a portion of another turbine casing  100  according to the present invention having a first reinforcing element  1   c  and a second reinforcing element  1   c ′ on an LPT casing section  5   c , as well as another first reinforcing element  1   d  on another LPT casing section  5   d.    
         [0066]    Reinforcing elements  1   c ,  1   c ′ and reinforcing element  1   d  are disposed within containment sections  16 . 
         [0067]    The further LPT casing section  5   d  has only one first reinforcing element  1   d . The further LPT casing section  5   d  has two shells or shell-shaped elements, the first shell being the part of LPT casing section  5   d  that is joined face-to-face with reinforcing element  1   d , and the second shell being the reinforcing element  1   d.    
         [0068]    Reinforcing elements  1   c ,  1   c ′ and  1   d  differ in the shape of the right end regions, as viewed in  FIG. 3 . 
         [0069]    The two reinforcing elements  1   c ,  1   c ′ are embodied as two layers or plies in face-to-face contact with one another. The upper of the two reinforcing elements  1   c  is secured from displacement in the axial direction (x-direction) by abutment of its end face against a fixing element  15   c , while the lower borders the radius of curvature of fixing element  15   d.    
         [0070]    Reinforcing element  1   d  is embodied as a single layer or ply. Reinforcing element  1   d  is formed with a curve or bend at the right end in the axial direction (x-direction) and is secured from axial displacement in the axial direction (x-direction) by means of fixing element  15   d.    
         [0071]      FIG. 4  shows, in simplified, schematic cross-sectional view, a portion of another turbine casing  100  according to the present invention having at least one wound band as a first reinforcing element  1   e  and a second reinforcing element  1   e ′. First reinforcing element  1   e  is disposed directly on exterior side  19  of LPT casing section  5   e.    
         [0072]    Reinforcing elements  1   e ,  1   e ′ include, for example, a wound wire or a wound composite material, which is wound in the circumferential direction of LPT casing section  5   e.    
         [0073]    The axial fixation of reinforcing elements  1   e ,  1   e ′ is accomplished in a manner analogous to the axial fixation in  FIG. 2  (see enlarged detail C). However, the geometric shapes, in particular surface geometry  19  of LPT casing section  5   e , are configured differently than surface geometry  19  of LPT casing section  5   b  in  FIG. 2 . Alternatively, the free ends of the wound material (wire, composite material, etc.) of reinforcing elements  1   e ,  1   e ′ may also be used for appropriate fixation. 
         [0074]    Reinforcing elements  1   e ,  1   e ′ may be applied by a single winding. 
         [0075]    The term reinforcing element as used herein is a structure meaning a reinforcement. 
         [0000]    
       
         
               
             
               
               
             
           
               
                   
               
               
                 List of Reference Numerals 
               
             
          
           
               
                 Reference 
                   
               
               
                 Numeral 
                 Description 
               
               
                   
               
               
                 100  
                 turbine casing 
               
               
                 x 
                 axial direction, main flow direction 
               
               
                 y 
                 radial direction 
               
               
                 1a, 1b, 1c, 
                 first reinforcing element 
               
               
                 1d, 1e 
               
               
                 1a′, 1b′, 
                 second reinforcing element 
               
               
                 1c′, 1e′ 
               
               
                 b″ 
                 third reinforcing element 
               
               
                  3 
                 interior side of the LPT casing section 
               
               
                  4 
                 flow direction 
               
               
                 5a, 5b, 5c, 
                 LPT casing section 
               
               
                 5d, 5e 
               
               
                  6 
                 bore 
               
               
                  7 
                 end region; curved ends of reinforcing elements 1a and 1a′ 
               
               
                  8 
                 bore diameter 
               
               
                  9 
                 abradable liner system 
               
               
                 11 
                 casing part 
               
               
                 13, 13′ 
                 further casing part 
               
               
                 15 
                 fixing element 
               
               
                 16 
                 containment section 
               
               
                 17 
                 bolted connection 
               
               
                 19 
                 exterior side of an LPT casing section 
               
               
                 21 
                 shoulder of the surface geometry of the LPT casing section