Abstract:
An annulus filler assembly for a rotor of a turbomachine, the assembly comprising: an annulus lid ( 56 ) having a radially outwardly facing surface ( 58 ) for forming an inner wall of a flow annulus of the rotor and a radially inwardly facing surface; and a frame for supporting the annulus lid ( 40 ), the frame being mountable to a disc of the rotor such that the annulus lid ( 56 ) is spaced away from the disc, wherein the frame ( 40 ) comprises a connection portion ( 46 ) which, in use, passes through an aperture ( 60 ) in the annulus lid ( 56 ) from the radially inwardly facing surface towards the radially outwardly facing surface ( 58 ) such that at least a portion of the connection portion ( 46 ) is visible from the radially outwardly facing surface ( 58 ); the assembly further comprising a locking element ( 68 ) which locks the connection portion ( 46 ) to the annulus lid ( 56 ) via the visible portion of the connection portion ( 46 ).

Description:
[0001]    The present invention relates to an annulus filler assembly for a turbomachine, in particular the bypass fan assembly of a turbo fan engine. 
       BACKGROUND 
       [0002]    A conventional turbo fan engine uses the core engine to drive a bypass fan mounted near the engine intake. Fan blades on the bypass fan drive a core flow into the core engine and a bypass flow around the core engine. The bypass flow combines downstream with the core exhaust flow to provide propulsive thrust. 
         [0003]    A casing assembly extends around the outside of the fan to provide an outer wall of a flow annulus through the fan. The fan blades themselves are not normally provided with blade platforms, and so a number of separate circumferential wall inserts or “annulus fillers” are mounted on the outside of the fan rotor disc, in between the fan blades, to form the inner wall of the flow annulus through the fan. 
         [0004]    The annulus fillers are typically mounted on the fan rotor disc using a hook arrangement, such as the one described in International Application PCT/GB93/00372 (published as WO93/21425). Here, each annulus filler is provided with a pair of hooks which extend radially inwardly from the filler to engage correspondingly shaped hooks provided on the outer face of the fan rotor disc. The hooks on the filler must be maintained in axial engagement with the hooks on the fan rotor disc, and one or more separate thrust rings is typically provided for this purpose. 
         [0005]    A similar configuration is shown in  FIG. 1 . A blade  2  is connected to a disc  4  at a radially outer face of the disc  4  by an interlocking configuration, such as a dovetail joint. A plurality of blades  2  are assembled onto the disc  4  around the circumference of the disc  4  to form a rotor. As described previously, an annulus filler  6  is provided between adjacent blades  2  so as to form the inner wall of the flow annulus through the fan. The annulus filler  6  is mounted to the disc by a pair of annulus filler hooks  8 ,  10  which engage with correspondingly shaped disc hooks  12 ,  14 . The hook arrangement provides radial retention of the annulus filler  6  against centrifugal loads experienced during operation of the rotor. A plurality of annulus fillers  6  are provided between each pair of adjacent blades  2 . To ensure that the annulus filler hooks  8 ,  10  are maintained in engagement with the disc hooks  12 ,  14 , the axial position of the annulus filler  6  with respect to the disc  4  is fixed by a nose cone support ring  16 . The nose cone support ring  16  covers the full circumference of the rotor and retains each of the annulus fillers  6 . The nose cone support ring  16  is connected to an arm  18  of the disc and also to an arm  20  of the annulus filler  6 . Consequently, the axial position of the annulus filler  6  is fixed so that the hooks remain engaged. During operation, the nose cone support ring  16  also bears a component of the centrifugal load of the annulus filler  6  which creates hoop stress in the nose cone support ring  16 . 
         [0006]    The nose cone support ring also functions as the primary fixation point for a nose cone of the turbomachine. The nose cone creates smooth airflow into the fan, particularly at the root of the blades, and also must be capable of withstanding bird strikes and preventing build up of ice. The nose cone  22  is located on an annular shoulder  24  of the nose cone support ring  16  and is connected at positions around the nose cone support ring  16  via abutting radial flanges  26 . 
         [0007]    The connection between the nose cone support ring  16  and the nose cone  22  is enclosed by a cover portion  28 . The forward (upstream) axial end of the annulus filer  6  has a tongue portion which is received under a lip portion  32  of the cover portion  28 . A similar arrangement is provided at the opposite axial end for mating with a rotating seal element  34 . 
         [0008]    A hook-type mounting arrangement such as the one described in International Application PCT/GB93/00372 and as shown in  FIG. 1  requires that dedicated, load-bearing attachment features such as hooks must be formed on the outside of a forged fan rotor disc and this adds to the cost and complexity of manufacturing the fan rotor disc. 
         [0009]    In addition, safely engaging the hooks with one another may be difficult and time-consuming because, in practice, the hooks tend to be obscured from view by the adjacent blades and by the annulus filler itself during assembly. Failure to safely engage the hooks increases the risk of annulus filler detachment under a centrifugal load during rotation of the fan. 
         [0010]    During a bird strike or fan blade off (FBO) event, a fan blade may be deflected and apply a circumferential load to an adjacent annulus filler. Tests have shown that some prior art annulus filler inserts secured using hook style fixings may be vulnerable to detachment under these circumferential loads. 
         [0011]    The present invention seeks to provide an improved annulus filler assembly, and in particular seeks to provide an annulus filler assembly which addresses one or more of the specific problems referred to above. 
       STATEMENTS OF INVENTION 
       [0012]    According to a first aspect of the invention there is provided an annulus filler assembly for a rotor of a turbomachine, the assembly comprising: an annulus lid having a radially outwardly facing surface for forming an inner wall of a flow annulus of the rotor and a radially inwardly facing surface; and a frame for supporting the annulus lid, the frame being mountable to a disc of the rotor such that the annulus lid is spaced away from the disc, wherein the frame comprises a connection portion which, in use, passes through an aperture in the annulus lid from the radially inwardly facing surface towards the radially outwardly facing surface such that at least a portion of the connection portion is visible from the radially outwardly facing surface; the assembly further comprising a locking element which locks the connection portion to the annulus lid via the visible portion of the connection portion. 
         [0013]    The annulus filler assembly of the present invention therefore provides allows visual inspection of the connections between the constituent components at each stage of assembly. This therefore removes the potential for mal-assembly which could lead to the disconnection of the annulus filler assembly when in service. 
         [0014]    The frame may be narrower than the annulus lid in a circumferential aspect. 
         [0015]    The frame may comprise a hook portion for mounting the frame to the disc of the rotor. 
         [0016]    The annulus lid and frame may be constructed from different materials. 
         [0017]    The frame may be constructed from metal. 
         [0018]    The metal frame is advantageous in the event of a fan blade off event. Here, the metal frame provides some degree of flexibility which would allow the annulus filler assembly to rotate when forced by a deflecting blade. Also if the annulus filler assembly were to fail as a result of a deflecting blade, it is likely that only the annulus lid would be disconnected. Therefore the mass and energy of the debris will be reduced, thus limiting damage. 
         [0019]    The annulus lid may be constructed from a composite material. 
         [0020]    The connection portion and locking element may comprise complementary interlocking surfaces which when interlocked prevent the connection portion from being withdrawn through the aperture. 
         [0021]    The connection portion and locking element may form a dovetail joint. 
         [0022]    The aperture may comprise first and second openings through which first and second portions of the connection portion pass and wherein the locking element is inserted between the first and second portions of the connection portion. 
         [0023]    The annulus lid may comprise a recess formed in its radially outwardly facing surface for receiving the locking element such that the locking element and radially outwardly facing surface form a substantially continuous inner wall of the flow annulus. 
         [0024]    The recess may be a channel extending in an axial direction along the radially outwardly facing surface and the locking element may be an elongate member slidably received within the channel. 
         [0025]    The first and second openings may be positioned either side of the recess. 
         [0026]    The locking element may be flexible. 
         [0027]    The locking element may lock a plurality of connection portions to the annulus lid. 
         [0028]    According to a second aspect of the invention there is provided a method of assembling a rotor, the method comprising: providing a plurality of annulus filler assemblies as claimed in any one of the preceding claims; coupling the frames of the annulus filler assemblies to a disc of the rotor; coupling a plurality of blades to the disc between adjacent frames; locating the annulus lid of the annulus filler assembly on the frame such that the connection portion passes through the aperture in the annulus lid; and inserting the locking element into the connection portion so as to lock the connection portion to the annulus lid. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]    For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made by way of example, to the following drawings, in which: 
           [0030]      FIG. 1  is a side cross-sectional view of a prior art annulus filler assembly; 
           [0031]      FIG. 2  is a perspective view of an annulus filler assembly in accordance with a first aspect of the invention in a first stage of assembly; 
           [0032]      FIG. 3  is a perspective view of the annulus filler assembly of  FIG. 2  in a second stage of assembly; 
           [0033]      FIG. 4  is a perspective view of the annulus filler assembly of  FIG. 2  in a final stage of assembly; 
           [0034]      FIG. 5  is a perspective view of an alternative embodiment of an annulus filler in accordance with a first aspect of the invention in a first state of assembly; 
           [0035]      FIG. 6  is a perspective view of part of an alternative embodiment of an annulus filler in accordance with a first aspect of the invention; and 
           [0036]      FIG. 7  is a perspective view of the annulus filler assembly of  FIG. 6  in a final stage of assembly. 
       
    
    
     DETAILED DESCRIPTION 
       [0037]      FIG. 2  shows an annulus filler assembly in accordance with a first aspect of the invention. The annulus filler assembly comprises a frame  40  having a first hook element  42  and a second hook element  44  for attachment to correspondingly shaped hook elements on a disc; for example the hooks  12 ,  14  shown in  FIG. 1 . 
         [0038]    The frame  40  comprises a pair of upstanding members  50  extending substantially from the first and second hook elements  42 ,  44  and a bridging member  52  which joins the first and second hook elements  42 ,  44  together. The frame  40  is constructed from sheet metal and therefore the bridging member  52  provides a degree of flexibility between the first and second hook elements  42 ,  44  which allows the first and second hook elements  42 ,  44  to engage with the hooks of the disc. 
         [0039]    The frame  40  comprises three connection portions  46  which are supported above the first and second hook elements  42 ,  44 . Two of the connection portions  46  are supported on the pair of upstanding members  50  and the third is supported by the bridging member  52 . Although three connection portions  46  are shown in  FIG. 2 , any appropriate number of connection portions  46  and a correspondingly arranged frame may be provided, in alternative applications. 
         [0040]    Each connection portion  46  has a cross-section which forms one half of an interlocking connection. For example, as shown in  FIG. 2 , each connection portion  46  has two shoulders  48  and a recess  49  therebetween, forming a female half of a dovetail joint. 
         [0041]    An arm  54  extends axially from the first hook element  42 . The arm  54  is connected to or abuts with a thrust ring, such as the nose cone support ring  16  shown in  FIG. 1 , which acts to position the annulus filler axially and to maintain engagement of the first and second hook elements  42 ,  44  with the hooks of the disc. 
         [0042]    The width w of the frame  40  is narrower than the gap between adjacent blades. This allows the frame  40  to be engaged with the disc prior to fitting of the blades and subsequent disassembly can be performed without removal of the frame  40  from the disc. As a result, it is possible to visually inspect the first and second hook elements  42 ,  44  and confirm whether they are correctly engaged with the hooks of the disc prior to fitting of the blades. In service, this also allows the blade flanks to be inspected without completely removing the annulus fillers and thrust ring. 
         [0043]    Alternatively, the frame  40  may be connected after fitting of the blades. Since the frame  40  is narrower than the gap between adjacent blades, there is a gap either side of the frame  40  which again allows visual inspection of the first and second hook elements  42 ,  44  to confirm that they are correctly engaged with the hooks of the disc. 
         [0044]    It should be appreciated that not all of the frame  40  need be narrower than the gap between adjacent blades and that alternatively only those elements which would otherwise restrict the view of the first and second hook elements  42 ,  44  may be narrower, particularly the pair of upstanding members  50  and the bridging member  52 . As can be seen in  FIG. 2 , the connection portions  46  do not directly overlie the first and second hook elements  42 ,  44  and therefore the first and second hook elements could be visible even if the connection portions  46  were of comparable width to the gap between adjacent blades. 
         [0045]    Referring now to  FIG. 3 , the annulus filler assembly is shown in a second stage of assembly. An annulus lid  56  is provided, which is constructed from a carbon-fibre reinforced plastic composite material and having a radially outwardly facing surface  58  for forming the inner wall of the flow annulus. The annulus lid  56  comprises three apertures  60  extending therethrough and a channel  62  running axially through the radially outwardly facing surface  58 . Each axial end of the annulus lid  56  is provided with a tongue  64  which is received under a lip portion of an adjacent casing component, such as the cover portion  28  and rotating seal element  34  as shown in  FIG. 1 . In other embodiments the annulus lid may alternatively be made from a metallic material. 
         [0046]    The annulus lid  56  is located onto the frame  40  such that the three connection portions  46  are received through the apertures  60 . The shoulders  48  of each connection portion  46  sit substantially flush with the radially outwardly facing surface  58  and a base of the recess  49  of the connection portion sits substantially flush with a base of the channel  62 . 
         [0047]    Alternatively, each aperture  60  may comprise two distinct openings  66  on either side of the channel  62  for receiving each of the shoulders  48  of a connection portion  46 . In this configuration the base of the recess  49  is separated from the channel  62  by the base of the channel. To compensate for the offset in the radial position of the base of the recess  49 , the shoulders  48  are radially taller so that they again sit flush with the radially outwardly facing surface  58 . 
         [0048]    In either configuration, the shoulders  48  and optionally the base of the recess  49  of the frame  40  are visible from radially outwards of the surface  58 , thus providing a visual confirmation that the connection portions  46  are correctly located in the apertures  60 . 
         [0049]    Referring now to  FIG. 4 , the annulus filler assembly is shown in a final stage of assembly. An elongate slider element  68  which is sized to be received in the channel  62  is introduced into the channel  62  by sliding the slider element  68  from an axially foremost end of the annulus lid  56  towards an axially rearmost end of the annulus lid  56 , as indicated by arrow  70 . The slider element  68  has a degree of flexibility which allows the slider element to form to the curvature of the annulus lid  56 . 
         [0050]    As the slider element  68  is slid through the channel  62  it passes through the shoulders  66  of each connection portion in turn. The slider element  68  has a male dovetail cross-section, such that when the slider element  68  is received in the connection portion  46  the two elements interlock to prevent the connection portion  46  from being withdrawn through the aperture  60 . Each axial end of the slider element  68  is provided with a bifurcated tongue  72 . Similarly to the tongues  64  of the annulus lid  56 , the tongues  72  are received under a lip portion of an adjacent casing component, such as the cover portion  28  and rotating seal element  34  as shown in  FIG. 1 . The cover portion  28  and rotating seal element  34  fix the axial position of the slider element  68  in relation to the annulus lid  56  and thus prevent movement during operation. 
         [0051]    As discussed previously, when correctly located, the shoulders  48  of the connection portions  46  sit substantially flush with the radially outwardly facing surface  58 . This therefore allows visual inspection before sliding the slider element  68  through the channel  62 . 
         [0052]    Where the connection portions  46  are not maintained in the correct position as the slider element  68  is slid through the channel  62 , depending on the degree of misalignment, the following outcomes will result:
       If misalignment is minor, the slider element  68  will be received sufficiently within the connection portion  46  and thus force the connection portion  46  radially outwards (or the annulus lid  56  radially inwards) through contact between the shoulders  48  of the connection portion  46  and the slider element  68 , particularly the tongue  72  of the slider element  68 , and thus any misalignment will be corrected;   If misalignment is moderate, the tongue  72  of the slider element  68  will contact the shoulders  48  and prevent the slider element  68  from sliding further;   If the misalignment is severe, an interlocking connection will not be formed and instead the slider element  68  will pass over the connection portion  46  withdrawing the connection portion  46  and shoulders  48  out of the aperture  60 .       
 
         [0056]    In the latter case where an interlocking connection is not formed, it is immediately evident from a visual inspection of the radially outwardly facing surface  58  that this is the case since the shoulders  48  are not visible, or if they are visible they are clearly not flush with the radially outwardly facing surface  58 . A visual inspection of the radially outwardly facing surface  58  therefore confirms whether the annulus lid  56  is correctly connected to the frame  40  and the assembly is not put into service unless all of the shoulders  48  of the connection portions  46  are visible and flush with the radially outwardly facing surface  58 . 
         [0057]    The slider element  68  is also provided with three recessed portions  74  spaced across the axial length of the slider element  68 . The spacing between the recessed portions  74  corresponds to the spacing between both the apertures  60  and the connection portions  46 . The recessed portions are offset from both the apertures  60  and the connection portions  46  when the slider element  68  is in its operative position wherein the tongues  72  of the slider element are axially aligned with the tongues  64  of the annulus lid  56 . By sliding the slider element  68  out of the annulus lid  56  (in the opposite direction to arrow  70 ) by a distance equal to the offset, the recessed portions  74  can be aligned with the connection portions  46  and apertures  60 . The recessed portions  74  have the shoulders of the dovetail cross-section removed so that the slider element  68  is narrower along these portions than the distance between the shoulders  48  of the connection portion  46 . Therefore, when the recessed portions  74  are aligned in this manner, the slider portion does not interlock with the connection portion  46  and the connection portion  46  can be withdrawn through the aperture  60 , thus allowing the removal of the annulus lid  56  from the frame  40  without having to fully extract the slider element  68  from the channel  62 . 
         [0058]    The reversed technique can also be used to connect the annulus lid  56  to the frame  40 . Here, the connection portion  46  is introduced into the aperture  60  when the recessed portions  74  are aligned with the apertures  60  and then the slider element is slid into the operative position to lock the connection portions  46  and prevent subsequent withdrawal. When correctly located, the shoulders  48  of the connection portions  46  sit substantially flush with the radially outwardly facing surface  58 . If the shoulders  48  of the connection portions  46  are not visible when the slider element  68  is in the operative position, it is clear that the annulus lid  56  is not correctly connected to the frame  40 . Therefore the requirement for visual inspection during all stages of assembly is satisfied with this technique also. 
         [0059]      FIG. 5  shows an alternative embodiment of a frame  140  for an annulus filler in accordance with a first embodiment of the invention. In contrast to the frame  40  shown in  FIG. 2 , the frame  140  has five connection portions  146  supported above the first and second hook elements  42 ,  44  (which are essentially identical to those of the frame of  FIG. 2 ). It will be understood that the slider and lid of this annulus filler, though not shown in the drawings, will be appropriately configured to interlock with the five connection portions  146 , in a similar manner to that described for the embodiment of  FIG. 2 . Because the slider and lid are supported in more places, the stresses and strains in the lid will be reduced, compared with the embodiment having three connector portions. 
         [0060]      FIG. 6  shows the underside of an alternative embodiment of a lid  156  for an annulus filler in accordance with a first aspect of the invention. As with the lid  56  shown in  FIG. 3 , the lid  156  comprises three apertures  60  extending therethrough, and a channel  62  running axially. In contrast to the lid  56  of  FIG. 3 , the lid  156  comprises longitudinal ribs  180 , which add stiffness to the lid and thereby lower the stresses therein. It will be understood that in other embodiments, different numbers or configurations of ribs or corrugations may be provided to achieve the same result. 
         [0061]      FIG. 7  shows an alternative embodiment of an annulus filler in accordance with a first aspect of the invention. In most respects, this embodiment is similar to that shown in  FIG. 4 , but the frame  240  of the annulus filler, instead of having first and second hook elements  42 ,  44  as in  FIG. 4 , has first and second mounting features  282 ,  284  comprising holes  286 ,  288 . In use, radial bolts (not shown) extend through the holes  286 ,  288  to secure the frame  240  to the fan disc. These radial bolts could form part of an axial retention system as described in our pending European patent application EP10168820.2. 
         [0062]    It will be appreciated that variations and modifications may be made to the specific arrangement described, without departing from the invention. 
         [0063]    For instance, the securing hooks  42 ,  44  may face each other. The interaction of the slider  68  and the annulus lid  56  and the connection portion  48  may be used to ‘lock’ the slider and lid in position through centrifugal force. 
         [0064]    In another arrangement (not shown in the drawings) the hooks  42 ,  44  face away from each other and the lip  54  becomes a secondary locking mechanism.