Patent Publication Number: US-2023160314-A1

Title: Turbine engine stator control valve comprising a continuous and free sealing ring

Description:
The subject of the invention is a turbine engine stator control valve comprising a continuous and free sealing ring. 
     The control valves in question herein are crowns of stationary blades, fastened to a casing of the stator and alternating with crowns of movable blades in the compressors and the turbines of the turbine engines. The blades are mounted on the casing of the stator by connections comprising imbrications of hooks, and the radially inner ends thereof are provided with seals, made of materials called abradable materials, cooperating with adjacent wipers (circular ridges), belonging to the rotor, to form labyrinth seals. This well-known design, however, requires a control of the clearances in the labyrinth seals, in order to minimise the leaks or, on the contrary, to prevent the premature wear of the abradable, which is achieved by means of a ventilation of the casing by a variable flow rate of pressurised fresh air originating from the compressors, to adjust its diameter through thermal expansions and therefore the radial position of the blades. The withdrawal of a portion of the air flow to combat the leaks through the seal however also imposes a reduction in the efficiency of the turbine engine, and the adjustment of the ventilation can prove to be difficult. In addition, the ventilation generally induces leaks between the sectors of the control valve, at the circumferential spaces which separate the platforms mounted circumferentially end to end. 
     The object of the invention is to reduce these drawbacks, and more specifically to reduce the flow rate of the residual leaks through the labyrinth seal, while alleviating or even eliminating the ventilation constraints of the casing around the concerned control valve. 
     The close prior art is represented, in particular, by US 2011/0135479A1, which describes a stator control valve where a bearing ring of an element of the labyrinth seal is continuous over a complete circumference and mounted at platform sectors which are directly connected to the stationary blades. The assembly is performed by imbrications of tabs extending in the tangential direction and which therefore only allow very small radial displacements of the ring in the sectors which surround it. A wave-shaped spring is disposed in a circular housing, and it bears on radially opposed forces of this housing, belonging respectively to the sectors and to the ring, to bring the latter back to an invariable position while damping the vibrations created by the rotor. The device is not designed to adjust the clearance between the ring and a rotor that it surrounds. 
     The invention relates, in a general form, to a turbine engine stator control valve comprising crown sectors which are disposed circumferentially end to end about an axis of the turbine engine, each of the sectors comprising at least one stationary blade which extends from a radially inner platform, a sealing ring carrying an abradable sealing element surrounded by the platforms of the sectors, the sealing ring being connected to the platforms by slide connections, characterised in that each slide connection includes a first sleeve secured to a sealing ring and a second sleeve secured to one of the platforms, the first and second sleeves being nested within each other by sliding and delimiting a housing, and each slide connection including a spring contained in the housing and constrained in the radial direction by being mounted, on the one hand, against one of the platforms and, on the other hand, against the sealing ring 
     The construction of the invention is therefore based on the joint presence of a continuous sealing ring, carrying the abradable, and the main portion of the control valve composed of angular sectors. The radial slides which connect them allow relatively significant radial deflections of the ring relative to the platforms by differential thermal expansion, as well as reduced deflections in the other directions (axial, tangential, and tilting) thanks to the low clearance between inner sleeves and the outer sleeves. The concentricity is maintained by the springs. As the transmission of heat between the ring and the platforms is more reduced in the invention than in other constructions, thanks to the fineness of connection ensured only by the slides, the ring is maintained more easily at a temperature close to that of the rotor than in other constructions, and its diameter can be adjusted independently of the radial position of the blade sectors, by the temperature of the gases passing in front of it. The invention improves sealing by the best adjustment of the clearances between the abradable and the wipers that can be hoped for, and also by the simple presence of the continuous ring, which interrupts the division of the control valve into sectors, at the radially inner end thereof. 
     According to various independent and optional improvements, generally contributing to the lightness and compactness of the construction:
         the housings contain radially oriented rods;   the springs are helical and threaded around the rods;   the rods belong to the platforms and comprise a radially inner free end entering a respective cavity of the ring and retained in said cavity;   the free ends of the rods are threaded and carry nuts alone which are retained in the cavities;   the number of the slides is equal to the number of the sectors.       

     Other aspects of the invention are a turbine equipped with the control valve according to the above, and a turbine engine including such a turbine. 
    
    
     
       The different aspects, features and advantages of the invention will emerge better from the comment on the following figures, appended for purely illustrative purposes and which completely represent an embodiment thereof: 
         FIG.  1    general arrangement of a control valve, in a design where it lacks the features of the invention; 
         FIG.  2    in perspective, an embodiment of the invention; 
         FIG.  3    the embodiment, in cross section; 
         FIG.  4    the embodiment, according to another perspective; 
         FIG.  5    a general view of a control valve. 
     
    
    
       FIG.  1    represents, in longitudinal section, a portion of a turbine engine in accordance with the known art and comprising a control valve crown  1  between two crowns of movable blades  2  and  3 . The control valve  1  comprises crown sectors  4  each comprising a few stationary blades  5  between an outer platform  6  and an outer platform  7  also extending over crown sectors. The outer platform  6  is fastened to a stator casing  8  by an assembly via an upstream hook  9  and a downstream hook  10  (the upstream and the downstream are understood relative to the general direction of the gases flowing in the turbine engine, for this entire description). A ventilation device is disposed outside the stator casing  8 ; it comprises tubular ramps  11  flowed through by flow rates of fresh gases subtracted from the compressor of the turbine engine, which extend substantially in line with the assembly via the hooks  9  and  10 , to blow fresh air therein through orifices  12 , to cool the stator casing  8  at the place of the assembly via the hooks  9  and  10  and therefore to adjust the local thermal expansions of the stator casing  6  and thus the radial position of the crown sectors  4  of the control valve  1 . 
     The radially inner platform  7  comprises an abradable seal  33  at the radially inner end thereof, which is directed radially inwards and forms a labyrinth seal with wipers  13  which are radially disposed facing each other, depending on a rotor  14  to which the crowns of movable blades, such as  2  and  3 , belong. Throughout this description, the axial X-X and radial R-R directions are considered with reference to the axis about which the turbine engine extends, the axial direction also corresponding to the axis of rotation of the rotor  14 . 
       FIGS.  2  to  4    are now contemplated. The sectors of control valve crowns  15  in accordance with the invention differ from those of known embodiments in that they comprise a radially inner platform  16  devoid of the abradable seal required to establish the sealing with the rotor  14 , an abradable layer which replaces it, now  17 , belonging to a ring  18 , which is continuous over a circumference, therefore common to the control valve crown sectors  15 . The ring  18  comprises annular inner sleeves  19  standing on the radially outer face thereof in the radial direction, and whose (radially outer) free end is open. The inner sleeves  19  slide in outer sleeves  20  standing on the radially inner face of platforms  16  in the radial direction and whose (radially inner) free end is also open. In addition to the inner sleeves  19 , the radially outer face of the ring  18  carries a planar outer rib  21  which extends along inner ribs  22 , which are also planar, of the control valve sectors  15 . The inner ribs  22  herein are joined to the outer sleeves  20 , without it being necessary. The inner sleeves  19  could be placed on the platforms  16 , and the outer sleeves  20  on the ring  18 . They are represented integral on the ring  18  and the platforms  16 , that is to say manufactured in same time as the ring and the platforms, by foundry for example, but it is possible to manufacture them separately and then fasten them by welding or otherwise. 
     The inner sleeves  19  and the outer sleeves  20  define cylindrical housings  23  in which radially oriented rods  24  extend, carried by the inner platforms  16  and comprising a threaded (radially inner) free end  25  on which a nut  26  is screwed. A helical spring  27  is threaded around the rod  24 . The inner sleeves  19 , outer sleeves  20  and springs  27  form slide connections  35  between the control valve sectors  15  and the ring  18  which allow the latter to be displaced in the radial direction, by contracting or expanding. The nut  26  of each rod  24  is disposed with a clearance in a cavity  28  delimited by several portions, which are assembled to each other, of the ring  18 , for example a cylindrical bandage  29  which constitutes the main structure thereof, and two frames  30  and  31  of portions of the abradable  17  which follow each other in the axial direction of the turbine engine. The cavity  28  is provided with a bore  32  to allow the threaded free end  25  and the rod  24  to extend outwardly and to slide with a sufficient clearance. 
     The spring  27  of each rod  24  is compressed between the inner platform  16  and the cylindrical bandage  29  of the ring  18 . This assembly allows the ring  18  to acquire a radial position determined exclusively by the thermal expansions that it undergoes, mainly due to the gas stream which circulates around it and crosses it by passing in front of the abradable  17 . There is in fact no connection between the rods  24  and the nuts  26 , housed with clearance in the cavities  28 , and the ring  18 . The axial position and the angular position of the ring  18  are ensured with sufficient accuracy by the sliding of the inner sleeves  19  in the outer sleeves  20 . The radial position of the ring  18  therefore becomes more or less independent from that of the control valve crown sectors  15  and is no longer governed by the ventilation devices, whose importance becomes less and whose elimination can even be considered. This radial position of the ring  18  can be evaluated with a sufficient accuracy to avoid the excessive clearances either in the labyrinth seal or on the contrary the premature wear of the abradable  17 , thanks to the knowledge of the predictable temperature of the gases circulating in the turbine engine. In particular, the outer rib  21  partially eliminates the leaks originating from the clearances at the inner platforms  16  of the crown sectors of the control valves  15  by covering a portion of the interstices therebetween at the location of the inner ribs  22 . 
     The connection of the ring  18  to the platforms  16  by the relatively few and low-bulk slides  35  contributes to the lightness of the construction, as well as the clogging of their interval only by the parallel ribs  21  and  22 , which do not have a structural role and may be fine. 
       FIG.  5    illustrates the complete control valve  34 . The slide connection  35  is present herein on each of the control valve crown sectors  15 , without it being necessary to properly support the ring. Three slides  35  could be sufficient; a number of three to twenty would be preferable to promote guiding the free expansion in operation. 
     The nuts  26  are used essentially to support the ring  18  during the assembly of the device. It is provided that the cavities  28  are wide enough to avoid stops of the nuts  26  regardless of the predictable thermal expansions of the ring  18 .