Abstract:
A casing section ( 30 ) for rotary apparatus ( 13, 14 ) of a gas turbine engine ( 10 ) is described. The casing section ( 30 ) comprises a partially circumferential casing member ( 32 ) and a plurality of radially inwardly extending vanes ( 34 ) fixed on the casing member ( 32 ).

Description:
FIELD OF THE INVENTION 
   This invention relates to casing sections. More particularly, but not exclusively, the invention relates to casing sections for casings of gas turbine engine compressors. 
   BACKGROUND OF THE INVENTION 
   Compressors for gas turbine engines comprise alternating annular arrays of stator vanes and rotor blades. The casings of the compressors are manufactured with annular slots into which the vanes are slid. The vanes are mounted on a platform. Each vane is made subject to manufacturing tolerances. These small variations in size become cumulative as the vanes are mounted onto the casing. This means that different sized vanes have to be used to ensure a close circumferential fit. 
   SUMMARY OF THE INVENTION 
   According to one aspect of this invention there is provided a casing section for a rotary apparatus of a gas turbine engine, characterized by a partially circumferential casing member and a radially inwardly extending vane fixed on the casing member. 
   Preferably, the casing section comprises a plurality of radially inwardly extending vanes fixed on the casing member. The, or each, vane is preferably integral with the casing member. 
   The casing section may be formed by casting, and the, or each, vane may be formed during such casting. The casing member and the, or each, vane are preferably cast integrally together. 
   Securing means is preferably provided to secure the casing section to an adjacent further casing or casing section. Where the further casing section is circumferentially adjacent said casing section, the further casing section is preferably as described above. 
   The securing means may comprise a flange extending axially across the casing member to secure the casing section to said further circumferentially adjacent casing section. In one embodiment, the securing means may comprise two of said axially extending flanges, one at each axially extending end of the casing member. Each flange may define one or more apertures to receive fastening means, for example bolts therethrough. 
   In another embodiment, the securing means may include a single flange, such flange being arranged along one of the axially extending edges of the casing member. Preferably, the casing section can be secured to a circumferentially adjacent casing section by suitable attachment means, for example welding or by the use of an appropriate adhesive. 
   The securing means may further comprise a circumferentially extending flange which may be provided on an appropriate circumferentially extending edge of the casing member for securing the casing section to an article, for example a casing, arranged upstream or downstream of said casing section. The flange may define one or more apertures to receive therethrough fastening means, for example in the form of a bolt to secure the casing section to said axially upstream or downstream casing. Preferably, a flange is defined on each of the upstream and downstream circumferentially extending edges of the casing member. 
   A radially inner member may be provided on the radially inner end of the, or each, vane. Preferably, the inner member extends across the radially inner ends of the vanes. Said inner member may comprise a platform which may extend across the radially inner ends of said plurality of vanes. 
   The casing member may have a radially inner face defining a recessed portion. The recessed portion is preferably downstream of the vanes. A lining may be provided in the recessed portion to provide a seal with the rotor blades and prevent air passing over the tips of the blades. Preferably, the lining is abradable to allow the tips of the rotor blades to cut a clearance path therethrough. 
   In one embodiment, the casing member may include two of said recessed portions and a lining material may be provided in each of the recessed portion. The recessed portions are preferably respectively provided upstream and downstream of the vanes. 
   A sealing means may extend radially inwardly from the inner member. Preferably, the sealing means provides an air seal. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings, in which: 
       FIG. 1  is a sectional side view of the upper half of a gas turbine engine; 
       FIG. 2  is a perspective view of one embodiment of a casing section; 
       FIG. 3  is a side view of a casing section shown in  FIG. 2 ; 
       FIG. 4  is a perspective view of another embodiment of a casing section; 
       FIG. 5  is a side view of a casing section shown in FIG.  4 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   With reference to  FIG. 1 , a ducted fan gas turbine engine generally indicated at  10  has a principal axis X—X. The engine  10  comprises, in axial flow series, an air; intake  11 , a propulsive fan  12 , a compressor region  113  comprising an intermediate pressure compressor  13 , and a high pressure compressor  14 , combustion means  115  comprising a combustor  15 , and a turbine region  116  comprising a high pressure turbine  16  an intermediate pressure turbine  17 , and a low pressure: turbine  18 . An exhaust nozzle  19  is provided at the tail of the engine  10 . 
   The gas turbine engine  10  works in the conventional manner so that air entering the intake  11  is accelerated by the fan to produce two air flows: a first air flow into the intermediate pressure compressor  13  and a second air flow which provides propulsive thrust. The intermediate pressure compressor  13  compresses the air flow directed into it before delivering that air to the high pressure compressor  14  where further compression takes place. 
   The compressed air exhausted from the high pressure compressor  14  is directed into the combustor  15  where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive the high, intermediate and low pressure turbine  16 ,  17  and  18  before being exhausted through the nozzle  19  to provide additional propulsive thrust. The high, intermediate and low pressure turbines  16 ,  17  and  18  respectively drive the high and intermediate pressure compressors  14  and  13  and the fan  12  by suitable interconnecting shafts. 
   The intermediate and high pressure compressors  13 ,  14  each comprise a casing  20 ,  22  which circumferentially surrounds and encloses axially alternating annular arrays of rotor blades and stator vanes  34  (see  FIGS. 2  to  4 ), although only the blades  24  of the intermediate pressure compressor  13  and the blades  26  of the high pressure compressor  14  can be seen in FIG.  1 . 
   Each of the arrays of stator vanes  34  is formed of a plurality of casing sections  30  arranged in an annular array. Referring to  FIGS. 2 and 3 , there is shown an embodiment of a casing section  30 . Each casing section  30  comprises a casing member  32  and a plurality of radially inwardly extending stator vanes  34  integrally fixed thereon the casing section  30  can be formed by casting, such that the casing member  32  and the vanes  34  are formed integrally by casting. 
   In the case of the embodiment shown in  FIGS. 2 and 3 , the casing section  30  has five of said stator vanes  34  which extend radially inwardly from a radially inner face  36  of the casing member  32 . A pair of circumferentially extending flanges  38 ,  40 , at the respective upstream and downstream edges  37 ,  39  of the casing member  32  connect each casing section  30  to respective upstream and downstream casings  41 A,  41 B (shown in broken lines in  FIG. 3 ) surrounding the respective upstream and downstream arrays of rotor blades  43 A,  43 B mounted on respective discs  143 A,  143 B. As can be seen, each of the flanges  38 ,  40  is provided with a plurality of apertures  43  through which bolts can be received to secure each casing section  30  to the respective upstream and downstream casings  41 A,  41 B. 
   The casing section  30  is attached to a circumferentially adjacent further casing section  30  by means of an axially extending flange  42 . The casing member  32  has two opposite axially extending edges  45 ,  47 . As can be seen, the casing section  30  comprises a single flange  42  which extends along one of the axially extending edges  47  of the casing member  32 . The opposite axially extending edge  45  is devoid of such a flange. In order to attach the casing section  30  to a circumferentially adjacent casing section  30 , the flange  42  is welded to the edge  45  of the adjacent casing section  30  and to ends  46 ,  48  of the respective circumferentially extending flanges  38 ,  40 . In the case of connections between adjacent axially extending, or adjacent circumferentially extending, flanges a gasket  38 A,  40 A,  42 A can be provided to prevent or reduce vibration. 
   The casing section  30  further includes a circumferentially extending platform  50 , which extends across the radially inner ends of the stator vanes  34 . The platform  50  of the casing section  30  can be attached to the platform  50  of a circumferentially adjacent further casing section  30  by suitable means, for example welding. 
   Rubstrips  52  are provided on a radially inner face  54  of the platform  50 . The rubstrips  52  sealingly engage members  55 A,  55 B on the discs  143 A,  143 B to prevent gas in the engine leaking from the higher pressure downstream region to the lower pressure upstream region. 
   The radially inner face  36  of the casing member  32  includes two radially outwardly extending shoulders  56 ,  58 . The shoulders  56 ,  58  are provided respectively upstream and downstream of the stator vanes  34 . The shoulders  56 ,  58  provide respective upstream and downstream recessed portions  60 ,  62  into which are received abradable linings  64 ,  66  which provide a seal for the upstream and downstream rotor blades. The upstream and downstream casings  41 A,  41 B also include respective corresponding recessed portions  68 A,  68 B, whereby the abradable linings  64 ,  66  overlap and are received in the respective recessed portions  68 A,  68 B. The linings  64 ,  66  provide a seal with the upstream and downstream rotor blades which carve a path through the respective abradable linings  64 ,  66 . Thus, in the event that the linings  64 ,  66  become worn, the respective casing section can be replaced to replace the lining  64 ,  66 . 
   Referring to  FIGS. 4 and 5  there is shown another embodiment, which comprises many of the same features of the embodiment shown in  FIGS. 2 and 3 , and these have been designated with the same reference numerals. However, the embodiments shown in  FIGS. 4 and 5  differs from that shown in  FIGS. 2 and 3  in that only one shoulder  58  and a corresponding recessed portion  62  is provided on the radially inner face  36  of the casing member  32 . The recessed portion  62  extends from the shoulder  58  to a radially inwardly extending flange  70  at the downstream edge  39  of the casing member  32 . A further difference is that upstream recessed portion  60  in the embodiment shown in  FIGS. 2 and 3  is omitted. Also omitted is the part of the casing member  32  upstream of the stator vanes  34 . In addition a flange  43  may be provided at the opposite axially extending edge to the flange  42  and both flanges  42 ,  43  may define apertures  49  for fastening means e.g. bolt or rivets to secure the casing sections together. 
   The upstream flange  38  is provided immediately upstream of the stator vanes  34 . 
   There is thus described a casing section for use in a gas turbine engine which has the advantage of reducing the part count in the assembly of a compressor, facilitates assembly, stripping, inspection of overhaul, reduces leakage, eliminates the need for selective assembly of the vanes, and does not require refurbishment of the abradable lining or the rod strip, since the casing sections can be replaced. 
   Various modifications can be made without departing from the scope of the invention. For example, each of the casings could be provided with circumferentially extending flanges at each of the actually extending edges, and these flanges could be provided with apertures for fastening means, for example in the form of bolts to enable circumferentially adjacent casing sections to be attached together. 
   In addition, although the invention has been described with reference to a compressor, it may also have applications in connection with turbines. 
   A further modification is that, although the casing has been described as being made of a plurality of casing sections, it will be appreciated that each casing section need not be identical, the number of vanes  34  extending radially inwardly from the casing members  32  may differ from casing section to casing section. 
   Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.