Seal for turbomachine blade

Abstract: A turbomachine is provided with a rotor assembly; a seal member 18 is mounted between a blade 12 and a rotor disc 11 of the rotor assembly, the seal member 18 rocking under centrifugal force about an axis 24 to give substantially straight line sealing contact 26, 27 therealong e.g. with the blade 12.

Description: This invention relates to a turbomachine e.g. a gas turbine engine, and is particularly concerned with a rotor assembly for use therewith. A rotor assembly for use in a turbomachine typically comprises a radially inner rotor disc having attached thereto a plurality of radially outer blades, said blades forming an annular array extending circumferentially around the disc. It is normal to provide for cooling of such a rotor assembly and passages for cooling fluid through the rotor disc and the turbine blades are usually provided but the presence of such passages requires the use of appropriate sealing means to minimise the loss of fluid. In particular in the case of a gas turbine wherein a compressor supplies compressed air for cooling as well as for combustion it is necessary that leakage be kept to the absolute minimum which requires the use of highly effective sealing means. Prior art devices have often been complicated by the need to incorporate blade-disc fastening means with the sealing arrangement, but the present invention utilises a relatively simple sealing arrangement which nonetheless works very effectively in practice and does not itself involve a blade-disc fastening arrangement. Any convenient fastening arrangement may, in fact, be utilised. A sealing device which retains the rotor blades and provides in operation pivoting due to centrifugal forces, sealing along a contact surface radially outwardly of the blade dovetail connection, is known, e.g., from US-A-5,257,909. The present invention is defined in claim 1. In a preferred arrangement the blade has a generally radially inwardly extending formation which provides a substantially straight edge providing said substantially straight line of contact with the seal member. The formation may be of generally rectangular cross-section and the seal member may have a planar surface which engages with the substantially straight edge defined by the formation. Further the seal member may have at least one projection extending radially outwardly from the planar surface, said projection being co-operable with the blade to restrict movement of the seal member in the axial direction of the rotor assembly. In an alternative arrangement, a formation of generally V-shaped cross-section is provided with the apex of the V constituting said edge and with the seal member having a pair of substantially planar surfaces which form a generally V-section recess. With this arrangement the included angle of the V of the V-shaped recess is greater than the included angle of the V of the V-section formation, and the apex of the V-section recess and the apex of the V-section formation will co-operate to provide said first sealing engagement. In this arrangement the generally V-section recess and/or the generally V-section formation are preferably non-symmetrical relative to a line bisecting the angle between the legs of the V. To manufacture a rotor assembly with a V-sectioned formation as delineated above, each seal member may initially be formed as an integral part of a respective said blade and be subsequently cut away therefrom, e.g. utilising a wire erosion method. Preferably, the radially inner part of the seal member has a curved surface for sealing with a correspondingly curved surface of the other of the disc and the blade, thereby to provide said second sealing engagement, and, measured axially of the assembly, the centre of gravity of the seal member is preferably further from the curved surface than is the substantially straight edge. In a preferred arrangement the rotor disc and each blade has a passage for cooling fluid, each said passage extending generally radially. Embodiments of the invention will be described by way of example with reference to the accompanying drawings wherein: Figure 1 is a section through a part of a rotor assembly according to the invention showing the arrangement of a seal member providing sealing between a radially inner region of a rotor blade and the radially outer region of the rotor disc when the rotor assembly is rotating; Figure 2 shows the arrangement of Figure 1 as viewed from one side thereof as indicated by arrow 'X' in Figure 1. Figure 3 is a section through a part of an alternative embodiment of a rotor assembly according to the invention. The rotor assembly 10 forms part of a gas turbine engine comprising a turbine, and one or more stages each comprising an annular array of stator vanes adjacent a said rotor assembly 10. Figures 1 and 2 illustrate part of the radially outer region of a rotor disc 11, and part of the radially inner region of a rotor blade 12, which blade 12 is one of a plurality arranged as an annular array circumferentially around rotor disc 11 to form the rotor assembly. The radially inner region of the rotor blade 12 constitutes a blade root whereby the blade 12 is secured to the rotor disc 11 to prevent axial and/or tangential movement of the blade relative to the disc. Securing takes place at a point along the axial length of the rotor intermediate of the two ends of the disc, and at one or both ends a sealing arrangement is provided. Thus, it is envisaged that the sealing arrangement illustrated in the drawings will be employed at each end of the disc/blade assembly or at one end only with alternative sealing means at the other end. The method of securing blade 12 to disc 11 may take any appropriate form but will usually involve some form of stud and socket, male/female, lobed or 'fir-tree' fastening arrangement. The stud or male part of the fastening will usually be provided on the blade root and the socket or female part of the fastening will be provided in the rotor disc. As seen in Figure 1, the rotor disc 11 and blade 12 have respective generally radially extending bores 15, 16 therethrough for the passage of cooling air, such cooling air having been directed to the passage 15 by the compressor of the turbine engine. For efficient operation and specifically to maximise compressor performance the interface spaces 17 between the disc 11 and the blade 12 must be sealed and a seal member 18 is provided at one or each axial end of the gap between the rotor disc and the blade. Each seal member 18 is mounted so as to be pivotable or rockable (in a clockwise direction as seen in Figure 1) about an axis 24 (see below) under centrifugal force as the rotor assembly rotates. Such axis 24 will be displaced from the centre of gravity 20 (see Figure 1) of the seal member. The seal member 18 has its under-surface, as shown, i.e. its radially inner surface 21 (see Fig. 2) of convex form and with a curvature corresponding to the curvature of an outer concave surface 22 of the rotor disc. Because of the rocking motion of the seal member 18, in use, the seal member 18 and the disc 11 make sealing contact (engagement) along curved line 23. Obviously the arrangement may utilise a concave surface on member 18 and a convex surface on disc 11. Sealing engagement between seal member 18 and blade 12 on the other hand takes place along a substantially straight line 24 which defines the axis about which the seal member pivots or rocks (see above). To that end, the blade root has a rectangular-section projection 25 extending generally radially inwardly, an edge 27 of which projection contacts a planar surface 26 of the seal member 18 to thereby constitute the said axis 24. Depending on the form and dimensions of the various components, the edge 27 and the planar surface 27 could be in at least light contact even when the rotor assembly is not rotating but, in any event, when the rotor assembly rotates the seal member 18 rocks under centrifugal force, the contact between planar surface 26 and the substantially straight edge 27 then operating so as to give sealing engagement therebetween. Thus as the rotor assembly rotates there is a (first) sealing engagement between the seal member 18 and the blade 12 at the substantially straight line of contact represented by axis 24 while at the same time there is a (second) sealing engagement between seal member 18 and disc 11 along curved line 23. Measured axially of the assembly the centre of gravity 20 of the seal member 18 is further from surface 21 than is the edge 27. Also, as seen on Figure 1, distance 'A' represents the distance measured axially of the assembly between the centre of gravity 20 of the seal member 18 and the axis 24 and 'B' represents the axial distance between axis 24 and curved line contact 23. Clearly 'B' is greater than 'A'. At its two ends the planar surface 26 has respective projections or toes 28, 29. These toes are not intended for sealing contact with the blade root but rather act to restrict axial movement of the seal member 18 - as seal member rocks in a clockwise direction edge 30 of projection 29 will eventually contact face 31 of blade 12, though care must be taken to ensure this does not happen during normal operation. The embodiment of Figure 3 involves a modified form of both seal member and blade root. The blade root 46 is formed with a projection 47 which has a generally V-shaped but non-symmetrical cross-section. The rockable seal member 49 on the other hand is formed at its radially outer region with a recess 50 having a generally V-shaped but non-symmetrical cross-section. The sections of the V-shaped projection 47 and of the recess 50 are similar but not identical. The straight line sealing contact (engagement) 43 between seal member 49 and blade root 46 occurs at the apices of the projection 47 and the recess 50 which respectively provide straight edges 48 and 53; to allow seal member 49 to rock about the substantially straight line of sealing engagement 43, the angle included by the legs of the V-shaped recess 50 is greater than that included by the legs of the V-shaped projection 47. The radially inner surface 52 of seal member 49, as before, is of convex form with a curvature corresponding to that of the concave surface of disc 11 to give curved line sealing engagement 44 as the seal member 49 rocks or pivot under centrifugal force. The embodiment of Figure 3 gives a particular manufacturing advantage. Thus the seal member 49 and the V-shaped projection 47 can initially be formed integrally e.g. by means of a locally enlarged formation of the casting of the blade. The seal member is then cut from the extra material, e.g. by a wire erosion method, to leave the projection 47 on the blade. It is possible by appropriate construction and arrangement of the parts for the substantially straight line of contact, which acts as the pivot axis of the seal member, to be provided on the disc; in that case, of course, the second sealing engagement which occurs when the seal member rocks or pivots will be between the seal member and a suitable formation on the blade.

Claims: A rotor assembly (10) for use in a turbomachine, the rotor assembly (10) comprising a radially inner rotor disc (11) to which a plurality of radially outer blades are attached by root portions (12) thereof and a respective seal member (18, 49) provided for sealing engagement between each blade root portion (12) and the rotor disc (11), wherein each seal member (18, 49) is mounted so as to be pivotable under centrifugal force about an axis, characterised in that the sealing engagement of the seal member occurs between a radially inner surface (27, 48) of the blade root portion and a radially outer surface (22) of the disc and said axis is defined by a substantially straight line of contact (24, 43) of the seal member (18, 49) with the disc or the blade root (11 or 12,46), the substantially straight line of contact (24, 43) also defining a first sealing engagement between the seal member (18, 49) and the disc or the blade root (11 or 12,46), and wherein the seal member (18, 49) is adapted to pivot under centrifugal force about said axis (24, 43), thereby to move into a second sealing engagement (23, 44) with the other of the disc or the blade root (11 or 12,46). A rotor assembly as claimed in Claim 1 characterised in that the blade (12) has a generally radially inwardly extending formation (25, 47) which provides a substantially straight edge (27, 48) providing said substantially straight line of contact (24, 43) with the seal member (18, 49). A rotor assembly as claimed in Claim 2 characterised in that the formation (25) is of generally rectangular cross-section. A rotor assembly as claimed in Claim 3 characterised in that the seal member (18) has a planar surface (26) which engages with the substantially straight edge (27) defined by the formation (25). A rotor assembly as claimed in Claim 4 characterised in that the seal member (18) has at least one projection (28, 29) extending radially outwardly from the planar surface (26). A rotor assembly as claimed in Claim 5 characterised in that a said projection (29) is co-operable with the blade (12) to restrict movement of the seal member (18) in the axial direction of the rotor assembly (10). A rotor assembly as claimed in Claim 2 characterised in that the formation (47) is of generally V-shaped cross-section with the apex of the V constituting said edge (48). A rotor assembly as claimed in Claim 7 characterised in that the seal member (49) has a pair of substantially planar surfaces which form a generally V-section recess (50). A rotor assembly as claimed in Claim 8 characterised in that the included angle of the V of the V-shaped recess (50) is greater than the included angle of the V of the V-section formation (47). A rotor assembly as claimed in Claim 8 or Claim 9 characterised in that the apex of the V-section recess (50) and the apex of the V-section formation (47) co-operate to provide said first sealing engagement (43). A rotor assembly as claimed in any one of Claims 7 - 10 characterised in that the generally V-section recess (50) and/or the generally V-section formation (47) are non-symmetrical relative to a line bisecting the angle between the legs of the V. A rotor assembly as claimed in any preceding claim characterised in that the radially inner part (21, 52) of the seal member (18, 49) has a curved surface for sealing with a correspondingly curved surface (23, 44) of the other of the disc or the blade (11 or 12), thereby to provide said second sealing engagement (23, 44). A rotor assembly as claimed in Claim 12 characterised by the fact that, measured axially of the assembly, the centre of gravity (20, 51) of the seal member (18, 49) is further from the curved surface than is the substantially straight edge. A rotor assembly as claimed in any preceding claim characterised in that the rotor disc (11) and each blade (12) has a passage (15, 16) for cooling fluid. A rotor assembly as claimed in Claim 14 characterised in that each said passage (15, 16) extends generally radially. A rotor assembly as claimed in any preceding claim characterised in that each blade (12) has a pair of axially spaced said seal members (18, 49), co-operating therewith and with the disc (11). A method of manufacturing a rotor assembly as claimed in Claim 7 or any claim appendant thereto characterised in that each seal member (49) is initially formed as an integral part of a respective said blade (12) and is subsequently cut away therefrom. A method of manufacturing a rotor assembly as claimed in Claim 17 characterised in that the seal member (49) is cut away utilising a wire erosion method. A rotor assembly when manufactured by the method as claimed in either Claim 17 or Claim 18. A turbomachine incorporating a rotor assembly as claimed in any one of Claims 1 - 16 or Claim 19.

Inventors: FAULKNER ANDREW ROWELL, FAULKNER, ANDREW ROWELL
Applicants: EUROP GAS TURBINES LTD, EUROPEAN GAS TURBINES LIMITED
Application year: 1997
Main classification: F01D11
IPC codes: F01D5, F02C7, F01D11