Abstract:
There is described a seal assembly for a gas turbine engine comprising: a first seal having a sealing passage which defines a flow path trajectory for leakage air, the first seal for partitioning a first pressure area to a lower pressure area; a second seal located along the line of the flow path trajectory of the first seal, the second seal for partitioning a second pressure area and the lower pressure area; a deflection member located between the first seal and second seal, and in the trajectory of the flow path from the first seal.

Description:
TECHNICAL FIELD OF INVENTION 
       [0001]    The present invention relates to a sealing arrangement for a gas turbine engine. 
       BACKGROUND OF INVENTION 
       [0002]      FIG. 1  shows a ducted fan gas turbine engine  10  comprising in axial flow series: an air intake  12 , a propulsive fan  14  having a plurality of fan blades  16 , an intermediate pressure compressor  18 , a high-pressure compressor  20 , a combustor  22 , a high-pressure turbine  24 , an intermediate pressure turbine  26 , a low-pressure turbine  28  and a core exhaust nozzle  30 . A nacelle  32  generally surrounds the engine  10  and defines the intake  12 , a bypass duct  34  and a bypass exhaust nozzle  36 . The engine has a principal axis of rotation  31 . 
         [0003]    Air entering the intake  12  is accelerated by the fan  14  to produce a bypass flow and a core flow. The bypass flow travels down the bypass duct  34  and exits the bypass exhaust nozzle  36  to provide the majority of the propulsive thrust produced by the engine  10 . The core flow enters in axial flow series the intermediate pressure compressor  18 , high pressure compressor  20  and the combustor  22 , where fuel is added to the compressed air and the mixture burnt. The hot combustion products expand through and drive the high, intermediate and low-pressure turbines  24 ,  26 ,  28  before being exhausted through the nozzle  30  to provide additional propulsive thrust. The high, intermediate and low-pressure turbines  24 ,  26 ,  28  respectively drive the high and intermediate pressure compressors  20 ,  18  and the fan  14  by concentric interconnecting shafts  38 ,  40 ,  42 . 
         [0004]    As will be appreciated, there is a need to compartmentalise the various sections of the engine so as to maintain the desired pressurised flow paths. The better this can be done, the more efficient the engine stands to be. However, the main gas path and inner core of the engine are made up from numerous parts which rotate relative to one another so sophisticated sealing technologies are required to seal between the relative rotating parts. 
         [0005]    Conventional gas turbine engines employ many different types of seals at different locations throughout the engine. Such seal types include non-contacting, contacting, air riding or compliant seals. 
         [0006]    A well utilised seal is a labyrinth seal. A labyrinth seal typically comprises a static part and a rotating part which are separated so as to be non-contacting in normal use. The rotating part includes a cascade of projecting annular fins which extend towards the static part. The opposing static part may include abradable portions which face the tips of the fins and preferentially abrade in favour of the fins if there is contact in use. Thus, the operating tolerance of the separating gap can be safely reduced to a minimum without fear of damaging the fins. 
         [0007]    Labyrinth seals, as well as many other seals, exit a jet of air from the last fin in the cascade. The present invention seeks to provide an improved sealing arrangement. 
       STATEMENTS OF INVENTION 
       [0008]    The present invention provides a seal assembly according to the appended claims. 
         [0009]    In a first aspect, the seal assembly is for a gas turbine engine and comprises: a first seal having a sealing passage which defines a flow path trajectory for leakage air, the first seal for partitioning a first pressure area to a lower pressure area; a second seal located along the line of the flow path trajectory of the first seal, the second seal for partitioning a second pressure area and the lower pressure area; a deflection member located between the first seal and second seal, and in the trajectory of the exit flow path from the first seal. 
         [0010]    The deflection member may be a fin. The fin may extend from a rotating part or a static part. The deflection member may be annular. 
         [0011]    The first pressure area may be a higher pressure area. The second pressure area may be an intermediate pressure area. 
         [0012]    The deflection member may be inclined in a downstream direction. The deflection member extends into the exiting flow path of the first seal. The deflection member may project from one side first seal exit to the other side of the first seal exit. 
         [0013]    The low pressure area may be contained within a low pressure chamber which includes an exit aperture in a wall thereof. The deflection member may be positioned between the exit of the first seal and the exit aperture of the low pressure chamber. 
         [0014]    The positioning of the deflection member may block the line of sight between the exit of the seal and the exit aperture. 
         [0015]    The low pressure chamber may be bounded by at least one wall located opposite the exit aperture. The deflection member may be angled to direct the flow towards the at least one wall and away from the exit aperture. 
         [0016]    A second deflection member may be located downstream of the second seal. The first and second deflection members may be axially spaced from one another. 
         [0017]    The second deflection member may be located on the at least one wall which opposes the exit aperture. 
         [0018]    The second deflection member may be angled away from the opposing wall such that the longitudinal axis of the wall points towards the exit aperture. 
         [0019]    The first and second deflectors may combine to provide a meandering flow path extending between the first seal exit and the exit aperture of the low pressure chamber. The meandering flow path may be chicane or s-shaped. Thus, the flow path includes first bend which turns the flow away from the exit aperture and towards a second turn. The second turn redirects the flow towards the exit aperture. 
         [0020]    The first seal may be a labyrinth seal. The second seal may a labyrinth seal. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0021]    Embodiments of the invention will now be described with the aid of the following drawings of which: 
           [0022]      FIG. 1  shows a longitudinal cross-section of a conventional gas turbine engine. 
           [0023]      FIG. 2  shows a schematic longitudinal cross-section of a seal assembly of the present invention. 
           [0024]      FIG. 3  shows a modification to the seal assembly shown in  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0025]      FIG. 2  shows a longitudinal cross-section of a seal arrangement  210  according to the present invention. The seal arrangement includes a first seal  212 , in the form of a stepped labyrinth seal, and a second seal  214 , in the form of a straight labyrinth seal, which are arranged in opposing flow directions. 
         [0026]    The first seal  212  is located between a high pressure area  216  and a low pressure area  218  and includes a static part  220  and a rotating part  222 . The rotating  222  and static  220  parts are radially separated to provide an annular shoot therebetween. The shoot extends axially and radially inwards so as to have a generally conical trajectory around the engine. The first seal  212  includes three stages which are axially and radially offset to one another along the length of the shoot. Each stage includes one or more fins  224  or teeth which extend from lands on the rotating part  222 . The fins  224  extend towards corresponding abradable portions  226  on the static part  220  and are inclined upstream towards the high pressure side of the seal. The fins  224  are annular and elongate in longitudinal section with a tapered profile which narrows towards the distal end. 
         [0027]    The low pressure area  218  is bounded by a radially inner  230  and radially outer  228  wall to form a chamber. The walls are continuations of the walls which define the first seal shoot. An exit aperture  232  for the low pressure air to flow out from the low pressure chamber is located in the radially inner wall  230 . 
         [0028]    The opposing end of the low pressure chamber  218  relative to the first seal, there is a second seal  214 . The second seal  214  is also a labyrinth seal in the form of a stepped labyrinth. The second seal  214  partitions an intermediate pressure area  234  from the low pressure area  218 . 
         [0029]    The first  212  and second  214  seal include sealing interfaces between the fins and corresponding static parts which define an imaginary axis which represents a general trajectory for the leakage flow through the seals. In  FIG. 2 , the general flow exit trajectory of the first seal  212  is towards the second seal  214 , and vice versa. Thus, air exiting the seals will be directed generally towards the opposing seal. The flow trajectory of the seal in the described embodiment is determined by the flow past the sealing fins. It will be appreciated that the exit flow trajectory of other fins may vary due to the architecture of the seals, but will be known by the person skilled in the art of air seals. 
         [0030]    The exit aperture  232  for the low pressure chamber is placed in an orthogonal relation to the exiting flow trajectories meaning that the flow must turn through ninety degrees before being exited from the chamber  218 . 
         [0031]    The high, intermediate and low pressures referred to in the embodiments are used in a relative sense. Hence, the high and intermediate pressure areas are at a higher pressure than the low pressure area and there is an expected dominating flow from the relative higher pressure areas to the low pressure areas. Typically, the air within the high pressure area will be provided by a stage of the high pressure compressor or one of the latter intermediate pressure compressor stages, with the intermediate pressure being provided by a stage of the intermediate pressure compressor, but this will vary upon application. 
         [0032]    It is well known that air exiting a non-contacting seal can form a powerful jet. The specific flow pattern of the jet is difficult to predict, but it can be assumed that the bulk trajectory of the jet will generally be in-line with the sealing interface. Thus, as shown in  FIG. 2 , the flow of air  238  exiting the first seal  212  is a jet predominantly directed away from the seal with a general trajectory more or less in line with the axial flow path through the seal  212 . Thus, if not disrupted or deflected in some way, the exiting flow would traverse the low pressure chamber  218  towards the second seal  214 . 
         [0033]    Due to the difference in the pressure being regulated by the first  212  and second  214  seals, there is generally a greater potential for the air exiting the first seal  212  to be of a considerably higher velocity than the air exiting the second seal  214 . In some operating conditions the velocity difference is potentially enough to disrupt or even reverse the flow exiting the second seal  214 . 
         [0034]    The described arrangement provides a deflection member in the form of a fin  236  at the downstream end of the first seal  212  which is located in the trajectory of the flow path of the air  238  exiting the final stage of the first seal  212 . Hence, the deflector fin  236  extends from a wall of the low pressure chamber on one radial side of the first seal to the other radial side of the first seal so as to cross the exit flow path trajectory. The deflector fin  236  is located on the rotating part  222  of the first seal and adjacent to the exit aperture such that the line of sight between the flow exit from the first seal and the exit aperture of the low pressure chamber is blocked by the deflector fin  236 . Additionally, the deflector fin  236  is angled away from the flow path in a downstream direction and acts to redirect the flow exiting the first seal away from the first seal  212  towards the outer wall of the low pressure chamber and away from the exit. The deflector fin  236  is tapered in a similar manner to the seal fins  224  described above. 
         [0035]    The inclination of the deflector fin is the same but in axial opposition to the seal fins. Hence, the deflector fin points axially downstream whereas the seal fin points upstream to aid sealing. Thus, the deflector fin and seal fin are substantially symmetrical about a plane which is normal to the axis of rotation so that the two components form a V-shape in section. The angle of the fins may be any appropriate respective angle for the sealing requirements and architecture of the engine. Thus, the angle of the deflector fin may be shallower if the exit aperture for the chamber is axially spaced further from the downstream end of the seal. It is envisaged that the angle of the deflector fin will be between approximately 45 and 65 degrees. 
         [0036]    In the example shown in  FIG. 3 , there is a sealing arrangement in which the features and reference numerals correspond with those of  FIG. 2 . In addition there is provided a second deflector fin  240  located adjacent the second seal  214  exit. The deflector fin  240  extends from a wall of the low pressure chamber on one radial side of the second seal to the other radial side of the second seal so as to cross the exit flow path trajectory. The deflector fin  240  is located on the static part  222  of the low pressure chamber and radially opposite the exit aperture. The deflector fin  240  is angled away from the flow path in a downstream direction towards the first seal  212  exit and exit aperture  232  and acts to redirect the flow exiting the second seal towards the exit aperture  232 . The deflector fin  240  is tapered in a similar manner to the seal fins  224  described above. 
         [0037]    The angling of the second deflector fin  240  helps turn the flow exiting the second seal but also provides a flow obstruction for the air which has been deflected by the first deflector fin  236 . Thus, in combination, the first and second deflector fins provide a meandering, S-shaped or chicane flow path for the air. The flow path includes a first bend which turns the flow away from the exit aperture and towards a second turn. The second turn redirects the flow towards the exit aperture. More specifically, the meandering flow path starts at the exit of the first seal before being turned by the first deflector fin to have a trajectory towards the exit opposing wall and the second deflector fin. The second deflector fin then turns the flow towards the exit aperture where it mixes with the exit flow from the second seal in a substantially parallel flow path which is less disruptive to the second seal exit flow. 
         [0038]    While the invention has been described in conjunction with the examples above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the examples set forth above are considered to be illustrative and not limiting and various changes to the described embodiments may be made without departing from the spirit and scope of the invention. For example, although the examples above relate to axially separated and opposing seals, it is possible that the seals could be radially separated and opposing. In this case, references to radial and axial set out above may become interchanged. Further, although the seals are shown as having exit flow trajectories which directly oppose one another, the invention may find benefit where one of the flow trajectories is not towards the exit of another seal. The sealing arrangements described above can be utilised any suitable location in a gas turbine engine and are not confined to a particular location or purpose.