Patent Publication Number: US-9835049-B2

Title: Turbomachine distributor comprising a thermal protection sheet with a radial stop, and associated thermal protection sheet

Description:
The invention generally relates to the field of turbomachines, and more particularly to thermal protection elements designed to be mounted in a distributor, for example a turbine annular distributor on a turbine housing. 
     A turbomachine example has been illustrated in  FIG. 5 . 
     A turbomachine typically includes a nacelle which forms an opening for admitting a determined air flow to the engine strictly speaking. Generally, the turbomachine comprises one or several sections  4  for compressing the air admitted into the engine (generally a low pressure section and a high pressure section) and a combustion chamber  5 , in which the thereby compressed air is mixed with fuel before being burnt therein. 
     The hot combustion gases from this combustion are expanded in the various turbine stages, generally including a high pressure stage  6  immediately downstream from the chamber  5  and which receives the gases with the highest temperature. After this first expansion, the gases are again expanded by being guided through the so-called low pressure stages  7 . 
     A low pressure turbine  7  conventionally includes one or several rows of turbine blades spaced out circumferentially all around the rotor of the turbine  7 . It also comprises a low pressure distributor  2  giving the possibility of directing the flow of gases from the combustion chamber  5  towards the turbine blades at a suitable angle and velocity in order to drive into rotation the blades and the rotor of the turbine  7 . 
     The distributor  2  comprises a plurality of blades positioned radially with respect to an axis of rotation of the turbomachine X connecting a radially internal annular element and a radially external annular element. The whole forms an annular vein facing the movable blades of the turbine. 
     More specifically, the low pressure distributor  3  is formed with fixed blades positioned in a wheel divided into a plurality of segments, circumferentially distributed around the axis X of the turbomachine. Each segment comprises several fixed adjacent blades secured to one element in a ring sector, as well as an upstream retention means and a downstream retention means. Here, upstream and downstream are defined by the direction of flow of the gases in the turbomachine. These retention means are for example annular rails made in the internal wall of the housing upon which will bear a supporting surface made on the ring sectors of the distributor segments. The assembly is laid out so as to allow relative expansion of the distributor with respect to the housing, depending on the speed variations of the engine. However, due to the axial symmetry of the distributor wheels and of the tangential forces resulting from the gas flow crossing them, provision has to be made for means blocking the rotating sectors. 
     For this, patent FR 2 743 603 in the name of the Applicant describes a method for mounting such distributor segments inside a housing. The segments of distributors comprise a peripheral outer rib, perpendicular to the axis of the distributor (and therefore of the turbomachine), bearing through upstream and downstream faces upon corresponding faces of the internal wall of the housing. A protrusion on the upstream face of the rib of each segment comprises a notch in which is accommodated an anti-rotation pin. This pin comprises a head accommodated in the notch and a rod slipped into a radial bore of the wall of the housing, and thereby prevents any rotary movement of the distributor segment around its axis. 
     In order to protect the wall of the housing against heat radiation from the distributor, notably from the low pressure distributor, a metal sheet is generally interposed between the distributor and the internal wall of the housing. This thermal protection metal sheet upstream bears against a radial surface portion made in the internal wall of the housing. The upstream edge of the protection sheet is radially curved inwards so as to form a hairpin which also bears upon an upstream edge of the distributor and participates in maintaining the latter against the upstream rail of the housing. Downstream, the protection sheet comprises an indentation with a tab in the bottom of the indentation. 
     This assembly gives entire satisfaction as regards maintaining the distributor inside the housing and thermal protection of the latter. 
     It was however ascertained that the metal sheet was able to disengage from its contact with the anti-rotation pin. As it is no longer retained, the tab risks rubbing against the internal face of the wall of the housing and causing &lt;&lt;fretting&gt;&gt; phenomena of the latter (wear of the wall). 
     It was therefore proposed to form, at the downstream end of the protection sheet, a radially curved edge inwards so as to form a hairpin in a similar way to its upstream end. This hairpin-shaped downstream edge then allows a surface-surface contact to be generated at the interface between the thermal protection metal sheet and the housing. However, this solution today seems difficult to produce, insofar that it requires implementation of a permanent ring on the metal sheet in order be able to form the hairpin-shaped downstream edge, this portion of the metal sheet cannot be removed from the mold. This solution is therefore expensive from the point of view of the final mass of the assembly just as from the point of view of its making. 
     Document FR 2 960 591, also in the name of the Applicant, and which is illustrated with reference to  FIG. 1 , proposes, as for it, a modification of the anti-rotation pin  40  so that it is used as an abutment for the tab in a possible radial displacement of the metal sheet during the operation of the turbomachine. Indeed, by interposing a stop between the portion of the metal sheet  10  which may move during operation, the risks of contact with the internal wall  30  of the housing are eliminated. For this, a shoulder  40   a  is formed on the anti-rotation pin  40 , a radially extending from the pin  40  between the tab  12   a  and the internal wall of the housing  30 . 
     Making this shoulder  40   a  however increases the overall cost for making the anti-rotation pin  40 , as well as its bulkiness. Document DE 100 48 156 describes a thermal protection metal sheet for a distributor, the downstream end of which is curved, adapted for coming into contact against a ring segment. 
     Finally, document DE 101 22 464 proposes a distributor comprising a thermal protection metal sheet, provided with elements forming a stop, adapted for bearing against the housing and preventing rotation of the distributor. Nevertheless, during expansions of the distributor, the elements forming a stop risk rubbing against the internal face of the housing and of wearing it out prematurely. 
     An object of the invention is therefore to propose means for blocking in rotation a segment of a distributor, notably a low pressure distributor of a turbomachine, with respect to a turbine housing of the turbomachine, which are further capable of protecting the housing from heat radiation from the distributor and of avoiding the risks of premature wear of the housing due to friction processes, and which are further of a moderate cost and easy to make. 
     For this purpose, the invention proposes a distributor for a turbomachine, notably a low pressure distributor, suitable for being mounted in a housing, comprising:
     a plurality of circumferentially distributed segments around an axis of rotation of the turbomachine,   a plurality of anti-rotation pins, mounted both on a segment of the distributor and on the housing, and   a thermal protection metal sheet, positioned between the housing and the segments of the distributor, comprising a plurality of tabs, each being adapted to bear against an anti-rotation pin.   

     The thermal protection metal sheet comprises at least one axial tab adapted to radially abut against a lower face of a first anti-rotation pin, and at least one radial tab adapted to axially abut against an upstream face of a second anti-rotation pin. 
     Certain preferred but non-limiting features of the distributor according to the invention are the following:
     the thermal protection metal sheet comprises a plurality of axial tabs and of radial tabs,   the thermal protection metal sheet substantially comprises as many radial tabs as there are axial tabs,   the radial tabs and the axial tabs alternate along the thermal protection metal sheet, around the axis of rotation of the turbomachine, and are separated by an indentation, preferably with material removal,   a circumferential width of said at least one axial tab corresponding to the distance separating three adjacent anti-rotation pins, and   said at least one axial tab is at a distance from the anti-rotation pin when the turbomachine is at rest.   

     The invention also proposes a protective thermal protection metal sheet able to be used in a distributor as described above, comprising at least one so-called radial tab, adapted to axially abut against an upstream face of a first anti-rotation pin, and at least one so-called axial tab, adapted to radially abut against aid lower face of a second anti-rotation pin. 
     Certain preferred but non-limiting features of a thermal protection metal sheet according to the invention are the following:
     it comprises a plurality of radial tabs and of axial tabs which alternate along said thermal protection metal sheet, and   the tabs are in one piece with said thermal protection metal sheet.   

     Finally, the invention proposes a turbomachine comprising a distributor as described above. 
    
    
     
       Other features, objects and advantages of the present invention will become better apparent upon reading the detailed description which follows, made with reference to the appended figures given as non-limiting figures and wherein: 
         FIG. 1  is a partial axial sectional view of a turbine distributor mounted in a housing of a turbomachine according to the prior art, 
         FIG. 2  is a partial axial sectional view of an exemplary turbine distributor mounted in a housing of a turbomachine according to the invention, 
         FIG. 3 a    is a perspective view of an exemplary thermal protection metal sheet according to the invention, 
         FIG. 3 b    is a detailed view of a portion of the thermal protection metal sheet of  FIG. 3   a,    
         FIG. 4 a    is a first perspective view of the example of  FIG. 2 , 
         FIG. 4 b    is a second perspective view of the example of  FIG. 2 , and 
         FIG. 5  illustrates an exemplary turbomachine onto which the invention is applied. 
     
    
    
     The invention will now be most particularly described with reference to a low pressure distributor  2  of a turbomachine  1 , mounted on a housing  3  of a low-pressure turbine  7 . 
     A low pressure distributor  2  is formed that with fixed blades positioned on a wheel divided into a plurality of segments  20 , circumferentially distributed around an axis of rotation X of the turbomachine  1 . Each segment  20  comprises several fixed adjacent blades secured to a ring sector element, as well as an upstream retention means and a downstream retention means. These retention means are for example annular rails  32 ,  24  made in an internal wall  30  of the housing  3  upon which supporting surfaces  22 ,  24  will bear, made on the ring sectors of the segments  20  of a distributor  2  as described above. 
     In order to block the sectors in rotation, the distributor  2  comprises a plurality of devices for blocking the segments, each comprising an anti-rotation pin  40 , mounted both on a segment  20  of the distributor  2  and on the turbine housing  3 . Similarly to what is described in document FR 2 960 951, a protrusion on the upstream face of each segment  20  comprises an indentation in which is accommodated the anti-rotation pin  40 . This pin  40  comprises a head  41  accommodated in the indentation and a rod  42  slipped into a radial bore of the wall  30  of the housing  3 , and thereby prevents any movement of rotation of the distributor segment  20  around the axis of the latter (corresponding to the axis of rotation X of the turbomachine). 
     A thermal protection metal sheet  10  is interposed between the segments  20  of the low pressure distributor  2  and the internal wall  30  of the turbine housing  3 , and adapted for limiting the heat radiation from the distributor  2  on the turbine housing  3 . This thermal protection metal sheet  10 , upstream, bears against a radial surface portion  33  made in the internal wall of the housing. Conventionally, the upstream edge  12  of the protection sheet  10  is radially curved inwards so as to form a hairpin. Optionally, the upstream edge may further bear upon an upstream edge of the segment  20  of the distributor  2  and participate in maintaining the latter against the upstream rail  32  of the housing  3 . 
     Downstream, the thermal protection metal sheet  10  comprises a plurality of tabs  14 ,  16 , each being adapted to bear against an anti-rotation pin  40  of the blocking devices. 
     In order to limit the risks of “fretting” generated by the contact between the thermal protection metal sheet  10  and the housing  3 , the metal sheet  10  is modified at its downstream portion. Indeed, the thermal protection metal sheet  10  comprises tabs  14 ,  16  adapted so that the metal sheet radially abuts and axially abuts against the anti-rotation pins  40 . The thermal protection metal sheet is therefore maintained in position against the anti-rotation pins  40 , while is displacement is limited in the direction of the internal wall  30  of the housing  3 . Here, by radial direction will be meant a direction extending substantially transversely with respect to the axis X of the turbomachine, and by axial direction will be meant a direction extending substantially parallel to the axis X of the turbomachine. 
     For example, the tabs  14 ,  16  of the thermal protection  10  may comprise axial tabs  14 , adapted to radially abut against the corresponding anti-rotation pin  40 , and radial tabs  16 , adapted to axially abut against the corresponding anti-rotation pin  40 . 
     Thus, the radial tabs  16  extends transversely with respect to the axis X of the turbomachine  1 , and give the possibility of maintaining in an axial position the thermal protection metal sheet  10  with respect to the distributor  2 . These radial tabs  16  therefore form axial stops. For this, the radial tabs  16  are for example laid out to extend facing an upstream face  46  of the anti-rotation pins  40 , this upstream face  46  corresponding to the face of the anti-rotation pins directed towards the upstream side of the turbomachine  1 , facing the gas flow. 
     The axial tabs  14 , as for them, substantially extend parallel to the axis X of the turbomachine  1 , and give the possibility of preventing the thermal protection metal sheet  10  from moving towards the turbine housing  3 , i.e. along a radial direction. This is why these axial tabs form radial stops. The axial tabs  14  are for example laid out to extend facing a lower face  44  of the anti-rotation pins  40 , this lower face  44  corresponding to the face of the anti-rotation pins  40  directed towards the axis of rotation X of the turbomachine  1 , facing the distributor  2 . 
     According to an embodiment, the thermal protection metal sheet  10  substantially comprises as many axial tabs  14  as there are radial tabs  16 . Thus, if the distributor  2  comprises twenty-six anti-rotation pins  40 , the thermal protection metal sheet  10  may for example comprise thirteen axial tabs  14  and thirteen radial tabs  16 . 
     The radial tabs  16  and the axial tabs  14  may moreover be distributed in alternation along the periphery of the thermal protection metal sheet  10 , in order to observe the symmetry of the turbomachine  1  and to balance the distributor  2 . 
     The thermal protection metal sheet  10  is preferably ring-shaped, and may be in one piece, i.e. in a single part, or obtained by association of several annular segments connected together. 
     The tabs  14 ,  16  may be formed integrally with the remainder of the thermal protection metal sheet  10 . For example they may be obtained by cutting the downstream edge of the thermal protection metal sheet  10  to form indentations  18 , with or without removal of material. In the embodiment illustrated in  FIGS. 1 to 4   b , the indentations  18  are made with removal of material, in order to avoid possible friction of the axial tabs  14  against the anti-rotation pin  40  upon thermal expansion of the distributor  2 . 
     Further, the thermal protection metal sheet  10  may comprise one tab  14 ,  16  per anti-rotation pin  40 , so that for a given anti-rotation pin  40 , the thermal protection metal sheet  10  has opposite either a radial tab  16 , or an axial tab  14 . Alternatively, the thermal protection metal sheet  10  may comprise one radial tab  16  and one axial tab  14  per anti-rotation pin  40 . A same anti-rotation pin  40  may then be found in radially abutting against an axial tab  14  and axially abutting against a radial tab  16 . 
     The axial tabs  14  may be wider (along the circumference of the thermal protection metal sheet  10 ) than the radial tabs  16 . For example, a circumferential width of an axial tab  14  may correspond to the distance separating three adjacent anti-rotation pins  40 . A given axial tab  14  may therefore not only extend facing the corresponding anti-rotation pin  40 , but also on either side of this pin  40  as far as the adjacent anti-rotation pins  40 , the adjacent anti-rotation pins  40  each being found facing another tab preferably a radial tab  16 . This embodiment actually gives the possibility of simplifying the making of the thermal protection metal sheet  10 , of reinforcing the resistance to radial forces of the axial tab  14  applied by the anti-rotation pin  40 , and of avoiding contact of the metal sheet  10  with the turbine housing  3  in spite of the vibrations to which the latter is subject, and also gives the possibility of obtaining better protection against heat radiation. 
     The radial tabs  16 , as for them, then have a width (along the circumference of the thermal protection metal sheet  10 ) substantially corresponding to the width of the upstream face  46  facing the anti-rotation pin  40 . 
     Alternatively, the radial tabs  16  are the ones which are wider than these axial tabs  14 , and they extend between three adjacent anti-rotation pins  40 , the axial tabs  14  then being of a width substantially equal to the width of the lower face  44  facing the anti-rotation pin  40 . 
     According to another further alternative, the axial tabs  14  and the radial tabs  16  are of equal width and extend on either side of each anti-rotation pin  40 , over a width globally equal to the distance between two adjacent anti-rotation pins  40 . 
     Optionally, the radial tabs  16  may be introduced into a groove made in the face facing the corresponding anti-rotation pin  40 . 
     Moreover, in the rest position, i.e. when the turbomachine  1  is not operating, the axial tabs  14  may extend facing the lower face  44  of the corresponding anti-rotation pins  40  and at a distance therefrom in order to allow a determined radial displacement of the thermal protection metal sheet  10  in the event of thermal expansion of the latter. This radial displacement is however limited, the axial tab  14  forming a radial stop when it comes into contact with the lower face  44  of the anti-rotation pin. Therefore there exists a space  19  between the axial tabs  14  and the lower surface  44  of anti-rotation pins  40 , when the distributor  2  is at rest. 
     On the other hand, the radial tabs  16  are in contact with the upstream face  46  of the anti-rotation pins  40 , regardless of whether the turbomachine  1  is at rest or operating, in order to maintain the thermal protection metal sheet  10  in position with respect to the distributor  2  and to the turbine housing  3 .