Abstract:
A turbine engine turbine ring, in particular for a helicopter, in which vibratory behavior is reduced. The turbine ring includes an essentially cylindrical support, and one or more sectors forming a circle configured to define a segment of an air passage, each sector being fastened to the support by an attachment device, wherein the attachment device includes a hook portion belonging to the support and projecting towards the sector, and a hook portion belonging to the sector and projecting towards the support, the hook portions of the support and of the sector being configured to co-operate in order to fasten the sector to the support, the ring further includes a damper device provided within the attachment device and stressed radially between a portion of the sector and a portion of the support so as to damp relative movements between the sector and the support.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a turbine ring for a turbine engine, in particular for a helicopter. 
         [0002]    Such a ring may be used in any type of turbine engine for the purpose of reducing the vibratory behavior that can appear within such rings. 
       STATE OF THE PRIOR ART 
       [0003]    In a conventional helicopter turbine engine, a high pressure turbine ring generally comprises a circle of sectors fastened to a ring support. As can be seen in  FIG. 2 , the sectors are provided for this purpose with hooks suitable for co-operating with hooks of the support. 
         [0004]    In contact with the air stream, the ring sectors are subjected to stresses from the aerodynamic stream, which stresses are caused in particular by the wake from upstream and downstream stages, and this can lead to vibratory behavior. In particular, in the operating range of the engine, the sectors can enter into resonance, a phenomenon that can lead to cracking due to vibratory fatigue or to phenomena of premature wear. 
         [0005]    At present, in order to achieve better control over such vibratory behavior, one technique for improvement consists in revising the specific shape of the sectors. Nevertheless, designing specific shapes is complex, given the imposed mechanical and aerodynamic stresses. 
         [0006]    Another known solution, which is easier to implement consists in reducing clearances when assembling rings. Nevertheless, radial clamping between the sectors and the support leads to additional mechanical stresses on the fastener hooks, and as a result they can suffer high levels of plastic deformation, and possibly also cracking. In addition, such an operation makes the procedure for mounting rings more complex, thereby increasing production and maintenance costs. 
         [0007]    There therefore exists a real need for a turbine ring, and for a turbine engine, avoiding at least to some extent the drawbacks that are inherent to the above-described known configurations. 
       SUMMARY OF THE INVENTION 
       [0008]    The present description provides a turbine ring comprising an essentially cylindrical support, and one or more sectors forming a circle configured to define a segment of an air passage, each sector being fastened to the support by an attachment device, wherein the attachment device comprises a hook portion belonging to the support and projecting towards the sector, and a hook portion belonging to the sector and projecting towards the support, the hook portions of the support and of the sector being configured to co-operate in order to fasten the sector to the support; the ring further comprises a damper device provided within the attachment device and stressed radially between a portion of the sector and a portion of the support so as to damp relative movements between the sector and the support; the damper device comes into contact in alternation, in the circumferential direction, with the inner surface of the support and with the outer surface of the hook portion of the sector. 
         [0009]    By using this damper device that maintains at least one pressure zone on said portion of the sector and at least one pressure zone on said portion of the support, relative movements between the sector and the support are constrained and thus smaller. In addition, they are damped radially by friction of the sector and/or the support against the damper device. This friction dissipates the energy of the sectors so it no longer accumulates, thereby reducing the risk of the sectors becoming resonant over the operating range, and thus greatly limiting damage due to vibratory fatigue. 
         [0010]    In addition, because of the damper device elastically constraining relative movements between the sector and the support, it is possible to maintain radial clearance between the sector and the support that is sufficient for limiting mechanical stresses of the oligocyclic fatigue type acting on the sector and the support, thereby increasing their lifetime. 
         [0011]    The damper device also makes it possible to release the sector from its secondary object of limiting vibration. Under such circumstances, its shape may be selected more freely: its shape can thus be simplified, thereby leading to cost reductions, or it may be optimized more effectively with respect to other functions of the sector. 
         [0012]    Furthermore, the damper device facilitates assembling the sector on the support by acting as a guide of radial dimension that corresponds substantially to the clearance that is to be left between the sector and the support: the sector can thus be pressed against the damper device in order to ensure it is accurately positioned. This improves positioning accuracy and repeatability, thereby leading to better control over clearance at the tips of the blade and reducing machining non-compliances. 
         [0013]    Such a configuration in which the damper device comes into contact in alternation in the circumferential direction with the inner surface of the support and with the outer surface of the hook portion of the sector ensures that the damper device can be shaped simply, since it does not have any need to provide continuous and simultaneous contact with the inner surface of the support and the outer surface of the hook portion of the sector. 
         [0014]    In certain embodiments, the damper device is also configured to press a portion of the sector against a portion of the support. Under such circumstances, relative movements of the sector and of the support can also be damped by friction of the sector against the support. 
         [0015]    In certain embodiments, the support is also fastened by means of a second attachment device analogous to the first attachment device; it is also provided with a second damper device that is provided within the second attachment device, and that is analogous to the first damper device. 
         [0016]    In certain embodiments, the damper device comprises a flexible blade. This flexible blade is preferably an element made of sheet metal. Such flexible sheet metal is inexpensive, easy to shape, and presents stiffness appropriate for such damping. 
         [0017]    In certain embodiments, the damper device is stressed radially between said portion of the sector and said portion of the support over its entire length. Under such circumstances, the stresses exerted on the sector and on the support are distributed over the entire length of the sector, and in addition damping is uniform over the entire sector. 
         [0018]    In certain embodiments, the damper device is substantially smooth over its entire length with the section of localized indentations distributed along its length. These may be constituted in particular by spherical bulges, e.g. made by stamping. 
         [0019]    In other embodiments, the device comprises an element made of corrugated sheet metal. 
         [0020]    In certain embodiments, the damper device is provided between an outer surface of the hook portion of the sector and an inner surface of the support. Such a configuration is easy to assemble, furthermore, in this configuration, the two hook portions are pressed against each other, thereby strengthening the fastening of the sector and improving its damping. 
         [0021]    In other embodiments, the damper device is provided between an inner surface of the hook portion of the support and an outer surface of the sector. 
         [0022]    In certain embodiments, the damper device is received at least in part in a groove formed in a portion of the sector. By means of this groove, it is possible to mount the damper device on the sector before assembling it on the support, thereby facilitating the procedure for assembly. In addition, this makes it possible to reduce the radial clearance between the sector and the support. 
         [0023]    In other embodiments, the damper device is received at least in part in a groove that is formed in a portion of the support. 
         [0024]    In certain embodiments, the damper device enfolds at least the distal portion of the hook portion of the support. The damper device is thus easily put into place and remains in position even in the absence of the sector. 
         [0025]    In certain embodiments, the damper device is configured so as to maintain permanently, firstly at least one pressure zone on the outer surface of the hook portion of the support and a pressure zone on its inner surface, and secondly at least one pressure zone on the inner surface of the hook portion of the sector and/or a pressure zone on an outer surface of the sector. The damper device is thus clipped around the end of the hook, thereby ensuring that it is put into position and held stationary. 
         [0026]    In other embodiments, the damper device enfolds at least the distal portion of the hook portion of the sector. 
         [0027]    In certain embodiments, the damper device is a single piece extending continuously all along the circumference of the ring formed by the sector(s). Nevertheless, it may be interrupted by a gap arranged in an azimuth plane of the device. 
         [0028]    In other embodiments, the damper device is divided into a plurality of sections that follow one another all along the circumference of the circle formed by the sector(s). 
         [0029]    In certain embodiments, a section of the damper device is associated with each sector. 
         [0030]    In other embodiments, each section of the damper device is associated with a plurality of sectors. 
         [0031]    In certain embodiments, the damper device is configured also to provide sealing between the support and the sector. For example, it may be a braided gasket. 
         [0032]    In certain embodiments, the damper device is secured either to the sector or to the support. This securing is preferably performed by welding. 
         [0033]    The present description also provides a turbine engine including at least one ring in accordance with any of the above-described embodiments. 
         [0034]    In certain embodiments, the turbine engine is a helicopter turboshaft engine. Said ring is fitted to the linked turbine and/or to the free turbine. 
         [0035]    In certain embodiments, the turbine engine is an airplane turbojet. 
         [0036]    The above-mentioned characteristics and advantages, and others, appear on reading the following detailed description of embodiments of the proposed ring and turbine engine. This detailed description makes reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0037]    The accompanying drawings are diagrammatic and seek above all to illustrate the principles of the invention. 
           [0038]    In the drawings, from one figure to another, elements (or portions of an element) that are identical are identified by the same reference signs. Furthermore, elements (or portions of an element) belonging to different embodiments but having analogous functions are identified in the figures by numerical references incremented by 100, 200, etc. 
           [0039]      FIG. 1  is an overall view of an example of a helicopter turboshaft engine. 
           [0040]      FIG. 2  is a cutaway perspective view of a first example of a turbine ring. 
           [0041]      FIG. 3  is an axial section view of the  FIG. 2  ring. 
           [0042]      FIG. 4  shows a variant of the  FIG. 2  ring. 
           [0043]      FIG. 5  is a cutaway perspective view of another variant of the  FIG. 2  ring. 
           [0044]      FIG. 6A  shows a variant of the damper device. 
           [0045]      FIG. 6B  is a radial section view of the  FIG. 2  ring provided with the  FIG. 6A  damper device. 
           [0046]      FIG. 7A  shows another variant of the damper device. 
           [0047]      FIG. 7B  is a radial section view of the  FIG. 2  ring provided with the  FIG. 7A  damper device. 
           [0048]      FIG. 8A  is an axial section view of a second embodiment of the ring. 
           [0049]      FIGS. 8B and 8C  are axial section views of variants of the  FIG. 8A  ring. 
           [0050]      FIG. 9  is an axial section view of a third embodiment of the ring. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0051]    In order to make the invention more concrete, example embodiments of turbine rings are described in detail below, with reference to the accompanying drawings. It should be recalled that the invention is not limited to these embodiments. 
         [0052]      FIG. 1  shows a turbine engine  10 , specifically a helicopter turboshaft engine. In conventional manner, the turboshaft engine  10  comprises a compressor  11 , a gas generator  12 , and both linked and free turbines  13  and  14 , also referred to as the high pressure turbine and the low pressure turbine, which are driven in rotation by the stream of burnt gas leaving the combustion chamber  12 . The free turbine  14  comprises a turbine wheel  14   a  that is fastened to one of the ends of a shaft  15 . The other end of the shaft  15  has a primary gearwheel  16  that meshes with an intermediate gearwheel  17 . The intermediate gearwheel  17  meshes with an outlet gearwheel  18 . The intermediate gearwheel  17  and the outlet gearwheel  18  are toothed wheels forming portions of the speed-reducing gearbox of the turbine engine  10 . The outlet gearwheel  18  is connected to an outlet shaft  19  for coupling to the main gearbox of the helicopter (not shown). The linked turbine  13  has a turbine wheel  13   a  that is connected to the compressor  11  via a drive shaft  20 . The linked turbine  13  is also fitted with a turbine ring  30  that defines the air flow passage and that faces the blades of the turbine wheel  13   a.    
         [0053]      FIG. 2  shows a first embodiment of such a turbine ring  30 . It comprises a generally cylindrical ring support  31  forming an integral portion of the casing of the turbine  13 , and a circle of ring sectors  32  fastened to the ring support  31  so as to define the air flow passage through the turbine  13 . 
         [0054]    As can be seen more clearly in  FIG. 3 , each ring sector  32  is fastened to the ring support  31  by using attachment devices  33   a  and  33   b : in each attachment device  33   a,    33   b,  a hook  34  of the sector  32  extends towards the support  31  in order to co-operate with a hook  35  of the support  31  extending towards the ring sector  32 . Each of these hooks  34  of the sector  32  thus possesses a radial portion  34   a  and a tangential portion  34   b,  which together extend continuously all along each sector  32 . Each hook  35  of the support  31  also has a radial portion  35   a  and a tangential portion  35   b,  which together extend circumferentially in continuous manner all along the circumference of the support  31 . 
         [0055]    In this first embodiment, the hooks  34  of the sector  32  are provided with respective ribs  41  projecting from the outside surface  34   e  of the hook  34  at least partially in line with the radial portion  34   a  of the hook  34 . This rib  41  serves to provide radial clearance between the outer surface  34   e  of the hook  34  and the inner surface  31   i  of the support  31  so as to enable a damper  50  to be put into place. 
         [0056]    The damper  50  is a flexible blade, preferably made of sheet metal, being substantially V-shaped in this axial section plane: this shape in section is substantially constant all along the length of the damper  50 . The damper  50  is thus stressed between the outer surface  34   e  of the hook  34  of the sector  32  and the inner surface  31   i  of the support  31  so as to exert firstly pressure on the hook  34  via its central zone, and secondly pressure on the support  31  via its two ends. 
         [0057]    The stiffness of this damper  50  may be adjusted by adjusting the thickness, the length, and more generally the shape of the damper. In particular, in this example, the damper is made using sheet metal having a thickness of about 0.2 millimeter (mm). Its material may also be selected as a function of the desired stiffness. Specifically, the metal sheet may be made of Inconel 718. 
         [0058]    As can be seen in  FIG. 2 , in this example, the damper  50  of each attachment device  33   a,    33   b  is a single piece extending continuously all along the ring support  31 , with the exception of a gap arranged in an azimuth plane of the damper  50  so as to make it easier to put into place in the turbine  13 . Nevertheless, in other examples, the damper could be continuous all along the ring support without including a gap. 
         [0059]    Numerous variants of this first embodiment are possible. For example, in the variant of  FIG. 4 , a groove  42  is formed in the outer surface  34   e  of the hook  34  of the ring sector  32 . Such a groove  42  serves to receive the damper  52 . The depth of the groove  42  is nevertheless shallower than the height of the damper  52  so that the damper  52  projects beyond the outer surface  34   e  of the hook  34 : the damper  52  is thus stressed between the support  31  and the hook  34  of the sector  32 . 
         [0060]    In addition,  FIG. 4  shows that it is generally possible to mount the damper  52  in a position that is the other way up relative to that of the damper  50  in  FIG. 3 : under such circumstances, the damper  52  exerts pressure on the inner surface  31   i  of the support  31  via its central zone, while exerting pressure on the hook  34  of the sector  32  via its two ends. 
         [0061]      FIG. 5  shows another variant of the first embodiment of the ring  30 . In this variant, the damper  54  is not a single piece but is made up of sectors: specifically, the divisions of the damper  54  are designed to correspond with the divisions of the ring sectors  32  so that a damper section  54  is associated with each sector  32 . Nevertheless, the damper  54  could naturally be divided in some other way. 
         [0062]      FIGS. 6A and 6B  show another variant of the first embodiment of the turbine ring  30 . Unlike the embodiment of  FIG. 3 , the damper  56  is not shaped over its entire length. In this variant, the damper  56  is a flexible blade, preferably made of sheet metal, that is substantially smooth over its entire length, with the exception of indentations  57  formed in regular manner in its smooth surface. As can be seen in  FIG. 6B , the damper  56  is configured so that its outer surface presses against the inner surface  31   i  of the ring support  31 , while the inner ends of the indentations  57  press against the outer surface  33   e  of the hook  33  of the ring sector  32  so that the damper device  56  makes contact in alternation in the circumferential direction with the inner surface  31   i  of the support  31  and with the outer surface  33   e  of the hook  33  of the ring sector  32 . 
         [0063]      FIGS. 7A and 7B  show a last variant of the first embodiment of the turbine ring  30 . In this variant, the damper  58  is a corrugated sheet with undulations enabling the damper  58  to come into contact in alternation along its circumferential direction with the inner surface  31   i  of the support  31  and the outer surface  34   e  of the hook  33  of the ring sector  32 . 
         [0064]      FIG. 8A  shows a second embodiment of the turbine ring  130 . In this second embodiment, the damper  160  is a flexible blade, preferably made of sheet metal, that is substantially U-shaped in this axial section plane, being engaged around the distal portion of the hook  135  of the support  131 , i.e. at the end of the tangential portion  135   b  of the hook  135 . The damper  160  thus has a plane portion  161  pressed against the distal surface of the hook  135 , from which there extend the two branches of the damper  160 . In a first portion  162 , the two branches extend towards each other so as to clamp onto the distal portion of the hook  135 , after which, in a second portion  163 , the two branches extend apart from each other so as to press firstly against the inner surface  134   i  of the tangential portion  134   b  of the hook  134 , and secondly against the outer surface  132   e  of the ring sector  132 . In this example, the two branches of the damper  160  are symmetrical. 
         [0065]      FIG. 8B  shows a variant of the second embodiment of the turbine ring  130 . In this variant, in order to obtain different stiffness, the inner branch of the damper  160  is longer than its outer branch. Thus, the second portion  163  of the inner branch presses against the outer surface  132   e  of the ring sector  132  further downstream than in the variant of  FIG. 8A . 
         [0066]      FIG. 8C  shows another variant of the second embodiment of the ring turbine  130 . In this variant, the inner branch of the damper  160  has a tapering first portion  162  that presses against the inner surface  135   i  of the hook  135 , but does not have a second portion pressing against the outer surface  132   e  of the ring sector  132 . 
         [0067]      FIG. 9  shows a third embodiment of a turbine ring  230 . In this third embodiment, the damper  260  is a flexible blade, preferably made of sheet metal, and it is substantially L-shaped in this axial section plane, being engaged around the distal portion of the hook  234  of the ring sector  232 . The damper  260  has a plane portion  261  pressed against the radial portion  235   a  of the hook  235  of the ring support  231 , with a generally tangential branch extending therefrom. In a first portion  262 , this branch extends towards the inside so as to press against the outer surface  234   e  of the hook  234  of the sector  232 , and then in a second portion  263 , this branch extends towards the outside in such a manner as to press against the inner surface  231   i  of the support  231 . Finally, this branch is folded radially inwards so as to press at right angles against the outer surface  234   i  of the hook  234 . The hook portion  234  of the sector  232  is thus pressed against the hook portion  235  of the support  231 . 
         [0068]    The embodiments described in the present description are given by way of non-limiting illustration, and a person skilled in the art, in the light of this description can easily modify these embodiments or envisage others, while remaining within the scope of the invention. 
         [0069]    In particular, all of the embodiments described relate to a linked turbine of the turbine engine, however the teaching can also be applied to a free turbine. Likewise, the teaching can be transposed directly to the field of airplane turbojets. 
         [0070]    Furthermore, the various characteristics of these embodiments can be used on their own or can be combined with one another. When they are combined, the characteristics may be combined as described above or in other ways, the invention not being limited to the specific combinations described in the present description. In particular, unless specified to the contrary, a characteristic described with reference to any one embodiment may be applied in analogous manner to any other embodiment.