Abstract:
A blade assembly for a rotary component comprises an aerofoil member and a displacement apparatus on the aerofoil member for displacing a detached first portion of the aerofoil member in a rearward direction relative to a second portion of the aerofoil member. On failure of the aerofoil member, the displacement apparatus displaces the first portion from the second portion in the rearward direction.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is entitled to the benefit of British Patent Application No. GB 0707426.3 filed on Apr. 18, 2007. 
       FIELD OF THE INVENTION 
       [0002]    This invention relates to blade arrangements. More particularly, but not exclusively, the invention relates to blade arrangements for rotary components of a gas turbine engine. Embodiments of the invention relates to blade arrangements for a fan of a gas turbine engine. 
       BACKGROUND OF THE INVENTION 
       [0003]    The fan of a gas turbine engine comprises a plurality of fan blades mounted on a hub. In the event of impact damage, each fan blade must be sufficiently robust to survive as a trailing blade in the event that portions of the immediately preceding blade are detached. The fan blades are reinforced to increase the stiffness, strength and mass of the blade. 
         [0004]    According to one aspect of this invention, there is provided a blade arrangement for a rotary component of an engine, the blade arrangement comprising an aerofoil member, a mounting support to support the aerofoil member and mount the blade on a hub, and a displacement means on the aerofoil member for displacing a detached first portion of the aerofoil member in a rearward direction relative to a second portion of the aerofoil member, the second portion remaining attached to the mounting support, whereby on failure of the aerofoil member, the displacement means displaces the first portion from the second portion in the rearward direction. 
         [0005]    The rotary component may comprise a fan, and the blade arrangement may comprise a fan blade arrangement. 
       SUMMARY OF THE INVENTION 
       [0006]    In one embodiment, the displacement means may comprise at least one passage extending across the aerofoil member. The displacement means may comprise a plurality of passages extending across the aerofoil member. 
         [0007]    The, or each, passage may hold a force applying medium to apply a force when released from the passage. The force applying medium may comprise a compressed fluid, such as a gas, whereby when the aerofoil member fails across the passage, the compressed fluid is released to apply the force on the first portion to displace the first portion rearwardly. 
         [0008]    Alternatively, the passages may be arranged in pairs. The passages of each pair may extend generally parallel to one another. A first fluid may be held in one passage of the, or each, pair. A second fluid may be held in the other of the, or each, pair. 
         [0009]    The first and second fluids may be reacable explosively with one another to provide the aforesaid force to the first portion. The first and second fluids may be hypergolic. The first fluid may comprise an oxidiser. The second fluid may comprise a fuel. 
         [0010]    Thus, in this embodiment, when the aerofoil member fails across the, or one, pair of passages, the first and second fluids are released from the passages to react explosively to apply the force to the first portion to displace it rearwardly. 
         [0011]    Suitable such first and second fluids may be as follows: liquid hydrogen and liquid oxygen; liquid fluorine and liquid hydrogen; liquid fluorine and hydrazine; FLOX-70 and berosene; nitrogen tetroxide and hydrazine; nitrogen tetroxide and monomethyl hydrazine; nitrogen tetroxide and unsymmetrical dimethyl hydrazine; nitrogen tetroxide and aerozine 50; red-fuming nitric acid and hydrazine; red-fuming nitric acid and monomethyl hydrazine; red-fuming nitric acid and unsymmetrical dimethtyl hydrazine; red-fuming nitric acid and aerozine 50; hydrogen peroxide and hydrazine. 
         [0012]    The, or each, passage may be angled across the aerofoil member such that the, or each, passage extends transverse to a direction of a line of failure across the aerofoil member, whereby the line of failure cuts through at least one passage, or one of pair of passages. The, or each passage may extend diagonally across the aerofoil member. 
         [0013]    In another embodiment, the displacement means may comprise a region of weakness on the leading edge of the aerofoil member, whereby failure of the aerofoil member occurs at said region of weakness. The region of weakness may be provided in an area of the aerofoil member such that the centre of gravity of the aerofoil member causes the aforesaid rearward displacement of the first portion on failure of the aerofoil member at said region of weakness. The region of weakness may comprise a fuse on said leading edge of the aerofoil member. If desired, the embodiment which includes the region of weakness may also include the aforesaid passage or passages as described above. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a sectional side view of the upper half of a gas turbine engine; 
           [0015]      FIG. 2  is a front view of the upper half of the fan of the gas turbine engine shown in  FIG. 1 ; 
           [0016]      FIG. 3  shows a blade arrangement with one embodiment of a displacement means; 
           [0017]      FIG. 4  shows the fan blade in  FIG. 3  after failure thereof; 
           [0018]      FIG. 5  shows a further blade arrangement with another embodiment of a displacement means; 
           [0019]      FIG. 6  shows the fan blade of  FIG. 5  after failure thereof; 
           [0020]      FIG. 7  shows a blade arrangement with a further embodiment of a displacement means; 
           [0021]      FIG. 8  shows the fan blade of  FIG. 7  after partial failure thereof; and 
           [0022]      FIG. 9  shows the fan blade of  FIG. 7  after total failure thereof. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0023]    Referring to  FIG. 1 , a gas turbine engine is generally indicated at  10  and comprises, in axial flow series, an air intake  11 , a propulsive fan  12 , an intermediate pressure compressor  13 , a high pressure compressor  14 , combustion equipment  15 , a high pressure turbine  16 , an intermediate pressure turbine  17 , a low pressure turbine  18  and an exhaust nozzle  19 . 
         [0024]    The gas turbine engine  10  works in a conventional manner so that air entering the intake  11  is accelerated by the fan  12  which 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 compresses the air flow directed into it before delivering that air to the high pressure compressor  14  where further compression takes place. 
         [0025]    The compressed air exhausted from the high pressure compressor  14  is directed into the combustion equipment  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 turbines  16 ,  17  and  18  before being exhausted through the nozzle  19  to provide additional propulsive thrust. The high, intermediate and low pressure turbine  16 ,  17  and  18  respectively drive the high and intermediate pressure compressors  14  and  13 , and the fan  12  by suitable interconnecting shafts  20 . 
         [0026]    Referring to  FIG. 2 , the fan  12  comprises a plurality of blade arrangements in the form of fan blade arrangements  22  mounted on a rotatable disc  24 . Each fan blade arrangement comprises an aerofoil member  30  and a mounting support in the form of a platform  32 . If, during operation of the engine  10 , the fan is struck by an incoming object, then one of the blade arrangements  22  can fail. The failure can take the form of a portion of the blade arrangement  22  becoming detached. A problem that can arise is that the detached portion can then be struck by the next blade arrangement  22  during rotation thereof. 
         [0027]    Referring to  FIG. 3 , there is shown a fan blade arrangement  22  which comprises the aerofoil member  30  and the platform  32  for securing the blade arrangement  22  to the hub  24  and upon which the aerofoil member  30  is mounted. 
         [0028]    In the embodiment shown in  FIG. 3 , the aerofoil member  30  defines a plurality of diagonally extending passages  34  which extend across the aerofoil member  30  in pairs. In each of pair of the passages  34 , one passage, for example labelled  34 A is filled with a first fluid material and the other passage of the pair, for example labelled  34 B in  FIG. 3  is filled with a second fluid material. The first and second fluid materials are selected such that they react explosively when mixed. 
         [0029]      FIG. 4  shows the blade arrangement  22  of  FIG. 3  after failure of the aerofoil member  30  in which a radially outer first portion  36  is detached from a radially inner second portion  38 . The second portion  38  is attached to the platform  32 . A line of failure  40  is shown extending across the aerofoil member  30 . The line of failure  40  extends through two pairs of the passages  34  which releases the first and second fluids from the passages  34 A,  34 B respectively, as shown by the arrows X and Y. 
         [0030]    The first and second fluids mix and spontaneously explodes, thereby imparting a force indicated by the arrow A on the first portion  36  to displace the first portion  36  in the direction of arrow A. 
         [0031]    The force on the first portion  36  is such that the first portion  36  is displaced rapidly in a rearward direction away from the trailing blade and therefore the trailing blade does not strike the detached portion  36  and is not damaged. 
         [0032]    Referring to  FIGS. 5 and 6 , showing embodiments which are generally the same as the embodiments shown in  FIGS. 3 and 4  with the exception that the passages  34  are not arranged in pairs, and instead extend singly in a diagonal direction across the aerofoil member  30 . In each of the passages  34  shown in  FIGS. 5 and 6 , there is provided a compressed fluid, such as a compressed gas. 
         [0033]    On failure of the aerofoil member  30 , as shown in  FIG. 6 , the line of failure  40  cuts across the passages  34 . The compressed gas in the passages  34  is as shown by the arrows X and Y. The release of the compressed gas imparts a force shown by the arrow A to displace the radially outer first portion  36  in the direction of the arrow A away from the trailing blades on the fan  12 . 
         [0034]      FIGS. 7 to 9  show a further embodiment, in which the mounting support  32  of the fan blade arrangement  22  is provided with a region of weakness  42  adjacent the platform  32 . The region of weakness is in the form of a fuse. The region of weakness  42  is provided on the leading edge  43  of the aerofoil member  30 , at the radially end region of the aerofoil member  30 , adjacent the platform  32 . When the aerofoil member  22  is struck by an object, the aerofoil member  30  fails at the region of weakness  42 . As shown in  FIG. 8 , a line of failure  44  extends part way across the aerofoil member  30  of the blade arrangement  22 . 
         [0035]    The centre of gravity G of the aerofoil member  22  is such that the radially outer first portion  36  rolls rearwardly as shown by the arrow B thereby increasing the length of the line of failure  44 . This rearward rolling of the first portion  36  continues until the first portion  36  becomes completely detached from the second portion  38  and is displaced from a rearward direction from the fan  12  away from the other blades  22 , as shown in  FIG. 9 . Thus, in this embodiment, the centre of gravity is such that it has a tendency to pull the failing first portion  36  of the main body  22  in a rearward direction, thereby tearing the aerofoil member  30  apart along the line of failure  44 . 
         [0036]    There is thus described a simple and effective way in which a failed blade of a fan of a gas turbine engine can be prevented from damaging other blades of the fan. 
         [0037]    Various modifications can be made without departing from the scope of the invention. For example, the angles of the passages  34  can be varied dependent upon the likely line  40  of failure across the blades. The angle of the passages can be selected such that the line of failure will cross at least one passage, or one pair of passages  34 .