Abstract:
A linear gasket for an inter-blade platform that presents a length, the gasket including a linear base for fastening to the inter-blade platform and a linear lip projecting from the linear base, the linear lip including a linear distal end portion configured to contact a pressure side wall or a suction side wall of a blade, a linear groove being formed between the linear base and the linear lip over at least a fraction of a length of the linear gasket. The linear distal end portion includes at least one linear slit extending over at least a fraction of the length of the gasket.

Description:
FIELD OF THE INVENTION 
     The invention relates to a linear gasket for an inter-blade platform. Such a linear gasket is arranged between a blade and a platform between blades and that is distinct from the blades, and it serves to limit the flow of air between the blade and the inter-blade platform. Such a blade is used particularly, but not exclusively, in fans, between the blades of the fan and the inter-blade platforms. 
     PRIOR ART 
     An inter-blade platform linear gasket is known that presents a length, the gasket comprising a linear base for fastening to the inter-blade platform and a linear lip projecting from the linear base, said linear lip presenting a linear distal end portion configured to contact a pressure side wall or a suction side wall of a blade, a linear groove being formed between the linear base and the linear lip over at least a fraction of the length of said linear gasket. That type of gasket extends along the pressure side or the suction side of a blade, including its leading edge and/or trailing edge. 
     The lip of that type of prior art gasket does not make it possible to fit closely to the blade in zones of sudden discontinuity or of small radius of curvature, such as for example in the vicinity of the leading edge or the trailing edge of the blade. As a result, air flows between the blade and the inter-blade platform in those zones. The sealing of the air (or gas) passage is thus not perfect, thereby degrading the performance of the gas turbine reaction engine. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to remedy the above-mentioned drawback, at least substantially. 
     The invention achieves this object by proposing a linear gasket of the above-specified type, wherein at least one linear slit extending over at least a fraction of the length of said gasket. 
     Below, the terms “gasket”, “base”, “lip”, “groove”, “slit”, and “distal end portion” may be used instead of “linear gasket”, “linear base”, “linear lip”, “linear groove”, “linear slit”, and “linear distal end portion”, in order to designate the same entities. Likewise, the term “platform” may be used instead of “inter-blade platform” to designate the same entity. 
     It can be understood that the linear gasket extends in a preferred direction, the longitudinal direction. This longitudinal direction is not necessarily rectilinear, and is preferably configured to follow the outlines of the blade, in particular in the vicinity of discontinuities of the blade. In other words, it can be considered that the length direction follows the neutral axis of the gasket. The length of the gasket is thus defined and measured parallel to this longitudinal direction. Likewise, the linear lip, the linear base, and the linear groove all extend along this longitudinal direction. The length of the lip, the length of the base, and the length of the groove are defined and measured likewise parallel to this longitudinal direction. It can be understood that the lip projects widthwise in a direction that is transverse relative to the longitudinal direction from the base. The groove is defined between the base and the lip in the portions of the gasket where the base and the lip form an angle of less than 90° (ninety degrees of angle), the angle being measured in a cross-section relative to the longitudinal direction. The linear distal end portion is a portion that extends lengthwise in the longitudinal direction, and widthwise over a distance of about 20% of the width of the lip. It can thus be understood that the linear distal end portion is arranged remote from the junction zone between the lip and the base. At least one linear slit is arranged in the linear distal end portion and extends in the longitudinal direction. 
     Because of the linear slit, the distal end portion is locally more flexible than the same distal end portion would be if it did not have such a slit. In comparison with gaskets of the prior art, the slit thus enables the lip to fit more closely to the outline of the blade, in particular in zones of the blade having a sudden discontinuity or a small radius of curvature. Furthermore, since the gasket is locally more flexible because of the slit, it adapts to the shape of the blade while being subjected to smaller mechanical stresses and wear than those to which prior art gaskets are subjected, thereby improving the lifetime of the gasket of the invention compared with prior art gaskets. 
     Preferably, the at least one linear slit is formed in a lip segment configured to contact the blade in the vicinity of a leading edge of the blade and/or in the vicinity of a trailing edge of the blade. 
     It can be understood that a lip segment is a portion of the lip considered in the longitudinal direction. The leading edge and the trailing edge of a blade are the regions that present the most sudden discontinuities. By placing a slit in the lip segments that are configured to come into contact with the blade in the vicinity of the leading edge and of the trailing edge, it is ensured that the gasket will fit as closely as possible to the wall of the blade, including in the vicinity of the leading edge and of the trailing edge. 
     Advantageously, the linear slit extends over the entire length of the linear lip. 
     In this configuration, it is ensured that the distal end portion presents local flexibility enabling the lip to match the shape of the contact surface of the blade all along its length. This provides the gasket with better ability to achieve leaktight contact with the wall of the blade. 
     Advantageously, the inter-blade linear gasket presents a cross-section that varies along the length of the gasket. 
     It can be understood that the shape of the cross-section of the linear gasket (i.e. its section on a plane perpendicular to the longitudinal direction of the gasket) varies in the longitudinal direction of the gasket. By having such a varying section, the gasket is adapted to fit as closely as possible to the blade depending on the shape of the blade. 
     In an embodiment, the cross-section of the platform varies and/or the cross-section of the lip varies. 
     Advantageously, the base presents a shoulder configured to co-operate with an edge of the inter-blade platform. 
     The linear gasket is generally arranged along an edge of a platform, said edge being for facing the pressure side or the suction side of the blade. Such a shoulder enables the gasket to be properly positioned relative to the platform while the gasket is being assembled on the platform. By means of such a shoulder, the gasket thus presents a protective portion covering said edge of the platform. Such a protective portion serves in particular to damp any impacts between the blade and the platform (or between facing portions of two adjacent platforms), should they come into contact. 
     Advantageously, inter-blade linear gasket includes at least one lip stiffener. 
     Such a stiffener serves to make the entire lip stiffer over a segment of the lip, the lip thus being pressed better against the wall of the blade. Thus, by means of the stiffener, the lip is pressed against the wall of the blade, whereas by means of the slit, the distal end of the lip is a close fit to the shape of the wall of the blade and provides leaktight contact. 
     The invention also provides an inter-blade platform including an inter-blade platform linear gasket of the invention. 
     The invention also provides a rotor comprising a disk having, mounted at its periphery, a plurality of blades and a plurality of inter-blade platforms, an inter-blade platform being arranged between each pair of adjacent blades, at least one of the inter-blade platforms including at least one inter-blade platform linear gasket of the invention. 
     Advantageously, the lip of said linear gasket is configured to co-operate with a blade root under a leading edge of said blade, in the vicinity of said leading edge. 
     In a height direction, a blade presents, in succession, a root followed by an airfoil, the root being the portion whereby the blade is fastened to the disk. The airfoil is the portion of the blade that interacts with air, this airfoil having a leading edge, a trailing edge, a pressure side, and a suction side. The root presents an intermediate portion that does not engage the disk. It can be understood that the gasket co-operates with the blade in this intermediate portion. The term “beneath” relates to the height direction of the blade, the blade root defining the bottom of the blade and the airfoil defining the top of the blade. Thus, by stating that the gasket is placed beneath the leading edge, it should be understood that the gasket is placed in the height direction towards the bottom of the blade relative to the transition zone between the root and the airfoil of the blade, in register with the leading edge. The term “in the vicinity” means that the gasket is arranged in the height direction in a zone extending over about 10% of the total height of the blade beneath the leading edge, and in the longitudinal direction in a zone centered on the leading edge and extending over about 20% of the length of the blade. 
     Advantageously, each of at least two inter-blade platforms has at least one inter-blade platform linear gasket of the invention, the at least two inter-blade platforms being adjacent to a common blade, said at least one linear gasket of an inter-blade platform from the at least two inter-blade platforms being arranged facing said at least one linear gasket of the other inter-blade platform from the at least two inter-blade platforms upstream from a leading edge and/or downstream from a trailing edge of each blade, said linear gaskets co-operating by pressing against each other upstream from the leading edge and/or downstream from the trailing edge of said blade. 
     The terms “upstream” and “downstream” refer to the flow direction of air (or gas) along the blade, the air flowing generally from the leading edge towards the trailing edge. It can be understood that each of two adjacent platforms on either side of a blade has a respective gasket of the invention on its edge facing said blade. These gaskets extend beyond the leading edge and beyond the trailing edge of the blade (i.e. the gaskets are longer than the blade), and they co-operate directly with each other by pressing against each other in these zones beyond the leading and trailing edges. The invention also provides a gas turbine reaction engine including a rotor of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention and its advantages can better understood on reading the following detailed description of embodiments of the invention given as non-limiting examples. The description refers to the accompanying drawing sheets, in which: 
         FIG. 1  shows a gas turbine reaction engine of the invention; 
         FIG. 2  is a fragmentary view of a section of the fan of the  FIG. 1  gas turbine reaction engine; 
         FIG. 3  is a fragmentary view in perspective of the gasket of the invention within the fan of the gas turbine reaction engine of the invention; 
         FIG. 4  shows the  FIG. 2  fan seen looking along arrow IV; 
         FIG. 5  shows the linear gaskets of  FIG. 4  on section V; 
         FIG. 6  shows the linear gaskets of  FIG. 4  on section VI; 
         FIG. 7  shows the linear gaskets of  FIG. 4  on section VII; 
         FIG. 8  shows the linear gaskets of  FIG. 4  on section VIII; 
         FIG. 9  shows the linear gaskets of  FIG. 4  on section IX; and 
         FIG. 10  shows a segment of the linear gasket of the invention in a perspective view. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       FIG. 1  shows a gas turbine reaction engine  100  including fan  80  forming a rotor of the invention. As shown in  FIG. 2 , the fan  80  comprises a disk  82  having mounted at its periphery both a plurality of blades  50  and a plurality of inter-blade platforms  40 , each blade  50  being interposed between two inter-blade platforms  40 . In other words, each platform  40  is arranged between a pair of adjacent blades  50 . In this example, each edge  42   a  and  42   b  of each platform  40 , facing the pressure side  52   a  and the suction side  52   b  of respective blades  50 , is provided with a respective linear gasket  10  or  10 ′ of the invention. Each linear gasket  10  and  10 ′ presents a respective linear base  12 ,  12 ′ and a linear lip  14 ,  14 ′, a respective linear groove  16 ,  16 ′ being formed between the base  12  and the lip  14  or between the base  12 ′ and the lip  14 ′. In this example, the gasket  10  is configured to co-operate with the blade  50  on its pressure side  52   a , while the gasket  10 ′ is configured to co-operate with the blade  50  on its suction side  52   b . Each blade  50  presents in succession along its height H, a root  51  followed by an airfoil  52 . The root  51  presents a portion  51   a  engaged in the disk  82  and an intermediate portion  51   b . The airfoil  52  presents the pressure side  52   a , the suction side  52   b , a leading edge  52   c , and a trailing edge  52   d  (cf.  FIG. 4 ). 
     In general, the pressure side wall and the suction side wall are substantially continuous (i.e. they do not show any significant differences) between the intermediate portion  51   b  of the root  51  and the airfoil  52 , such that the pressure side wall and the suction side wall of the blade at the root of the blade are sometimes also referred to as the pressure side and the suction side. 
     As shown in  FIG. 3 , the lip  14  of the gasket  10  co-operates with the root  51  of the blade  50  beneath the leading edge  52   c  of the blade  50  in the vicinity of said leading edge  52   c . Although not shown, the gasket  10 ′ co-operates likewise with the root  51  of the blade  50 , beneath the leading edge  52   c  of the blade  50 , in the vicinity of said leading edge  52   c . It should be observed that  FIG. 3  is a fragmentary view that shows only a portion of the blade  50  (a portion of the intermediate portion  51   a  and a portion of the airfoil  52 ), together with a portion of the platform  40  and a portion of the gasket  10 . 
       FIG. 4  is a view of a blade  50  together with two platforms  40  seen looking along arrow IV of  FIG. 2 . The gaskets  10  and  10 ′ extend from upstream of the leading edge  52   c  of the blade  50  to downstream of the trailing edge  52   d  of the blade  50 . Thus, each gasket  10  and  10 ′ presents a segment  10   a ,  10 ′ a  that extends upstream from the leading edge  52   c , a segment  10   b ,  10 ′ b  that extends facing the pressure side  52   a  or the suction side  52   b  respectively of the blade  50 , and a segment  10   c ,  10 ′ c  that extends downstream from the trailing edge  52   d  of the blade  50 . “Upstream” and “downstream” are considered relative to the flow of air as represented by arrow C flowing along the blade  50 , with the arrow C pointing from upstream to downstream. Each gasket segment extends over a longitudinal portion of the gasket. The longitudinal directions of the gaskets  10  and  10 ′ are represented by respective dashed lines L and L′. The upstream segments  10   a  and  10 ′ a  face each other such that the lips  14  and  14 ′ of the gaskets  10  and  10 ′ co-operate by bearing against each other in the zone upstream from the blade  50  (cf.  FIG. 5 ). Likewise, the downstream segments  10   c  and  10 ′ c  face each other so that the lips  14  and  14 ′ c  of the gaskets  10  and  10 ′ co-operate by pressing against each other in the zone downstream from the blade  50  (cf.  FIG. 9 ). 
     In the zones that are configured to come into contact with the vicinity of the leading edge  52   c  and of the trailing edge  52   d , the gaskets  10  and  10 ′ present linear slits  120  &amp;  122  and  120 ′ &amp;  122 ′ (cf.  FIGS. 5, 6, 8, and 9 ). These slits  120 ,  122  and  120 ′,  122 ′ extend respectively along directions that are substantially parallel to the longitudinal directions L and L′. It should be observed that along the outline of the blade  50 , the longitudinal directions L and L′ are substantially parallel to the walls of the blade  50 . 
     As shown in  FIGS. 5 and 6 , the linear distal end portions  14   a  and  14 ′ a  have respective linear slits  120  and  120 ′. Each of these  FIGS. 5 and 6  shows a section of the assembly comprising a blade and platforms as shown in  FIG. 4  in the vicinity of the leading edge  52   c  of the blade  50 . Directions B and B′ that are respectively substantially parallel to the lips  14  and  14 ′, indicate the respective width directions of the lips  14  and  14 ′. The “distal” nature of the distal end portion is considered along these directions B and B′, the distal end portion of a lip being remote from its base along the width direction of the lip.  FIG. 7  is a section through the assembly of a blade and platforms as shown in  FIG. 4  in a zone that is distinct from being in the vicinity of the leading edge  52   c  or of the trailing edge  52   d  of the blade  50 . In this zone that is distinct from the vicinity of the leading edge  52   c  and of the trailing edge  52   d , the gaskets  10  and  10 ′ do not present any linear slit. In the same manner as in the vicinity of the leading edge  52   c , the gaskets  10  and  10 ′ present respective slits  122  and  122 ′ in the vicinity of the trailing edge  52   d  in the distal end portion  14   a  of the lip  14  and in the distal end portion  14 ′ a  of the lip  14 ′, as shown in  FIGS. 8 and 9 . 
     The cross-section of the gaskets  10  and  10 ′, and more particularly of the base  12  and of the lip  14  of the gasket  10  and of the base  12 ′ and of the lip  14 ′ of the gasket  10 ′, varies along the longitudinal direction L or L′, as can be seen in  FIGS. 5 to 9 . 
       FIG. 10  shows a segment of gasket  10  including stiffeners  18 . In this example, each stiffener  18  is in the form of a rib formed integrally with the gasket  10 . In a variant, a stiffener is formed by reinforcement arranged in the thickness of the lip, or indeed by a sheath arranged around the lip. Such stiffeners may also be provided for the gasket  10 ′. 
     The gaskets  10  and  10 ′ present respective shoulders  20  and  20 ′ arranged in the thickness of the base  12  or  12 ′. Thus, each of the bases  12  and  12 ′ presents a protective portion  12   a  or  12 ′ a  respectively covering the edge  42   a  or  42   b  of a platform  40 . As shown in  FIGS. 4 to 9 , the protective portions  12   a  and  12 ′ a  are thicker in the segments  10   a ,  10 ′ a  and  10   c ,  10 ′ c  (i.e. upstream from the leading edge and downstream from the trailing edge) than in the segments  10   b  and  10 ′ b . These greater thicknesses in these zones serve in particular to stiffen the gaskets  10  and  10 ′ in the zones and prevent the lips from folding outwards (i.e. occupying positions beside the airfoil  52  of the blade). 
     The gaskets  10  and  10 ′ are preferably made of plastic elastomer and they are fabricated by molding. 
     Although the present invention is described with reference to specific embodiments, it is clear that modifications and changes may be made to those embodiments without going beyond the general ambit of the invention as defined by the claims. In particular, individual characteristics of the various embodiments shown and/or mentioned may be combined in additional embodiments. Consequently, the description and the drawings could be considered in an illustrative sense rather than a restricted sense.