Abstract:
A gas turbine diffuser assembly and a method for assembling same, includes providing a loose fit between the diffuser body and the diffuser pipes. Damper members provide a snug attachment.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to gas turbine engines, and more particularly to a compressor diffuser assembly for gas turbine engines.  
       BACKGROUND OF THE INVENTION  
       [0002]     Conventionally, the diffuser pipes are inserted very tightly into the orifices of the diffuser ring, in order to reduce leakage of pressurized air to improve the efficiency of engine performance, and to secure them against dynamic excitation. The tight fit is difficult to achieve, thereby increasing manufacturing expenses.  
         [0003]     Therefore, there is a need for an improved compressor diffuser assembly which is low cost and durable.  
       SUMMARY OF THE INVENTION  
       [0004]     One object of the present invention is to provide a compressor diffuser assembly for gas turbine engines.  
         [0005]     In accordance with one aspect of the present invention, there is provided a diffuser assembly for a gas turbine engine, the diffuser comprising an annular diffuser body having a plurality of orifices disposed circumferentially around an outer periphery thereof, the orifices having an inner wall, a plurality of diffuser pipes each having a first end thereof received in one of the orifices adjacent the inner wall thereof, and a flexible damper member disposed between the first end and the inner wall of at least one of the orifices.  
         [0006]     In accordance with another aspect of the present invention, there is provided a centrifugal compressor system of a gas turbine engine, the compressor system comprising an impeller assembly driven by a shaft of the engine for generating a pressurized air flow, an annular diffuser body having a plurality of orifices disposed circumferentially spaced apart in an outer periphery thereof, the annular diffuser body being downstream of the impeller for directing the pressurized air flow, a plurality of diffuser pipes inserted at a first end thereof into the orifices of the annular diffuser body, each of the diffuser pipes having a cross section expanding towards a second end thereof, and a damper member disposed between the first end of the diffuser pipes and the orifices, thereby providing a snug attachment of the diffuser pipes to the orifices of the annular diffuser body.  
         [0007]     In accordance with a still further aspect of the present invention, there is a method for assembling a centrifugal compressor diffuser for gas turbine engines, the method comprising providing diffuser pipes having a first end diameter, providing a diffuser body having orifices for receiving the pipes, the orifices having a diameter sufficiently larger than the first end diameter such that a loose fit is provided when the first end is inserted into the orifice, providing a damper member in at least one of the orifices and said first ends of the diffuser pipes, and inserting the diffuser pipe first ends into the orifices so that the damper member is disposed between the first ends and the orifices to thereby provide a snug attachment therebetween.  
         [0008]     The present invention advantageously provides a compressor diffuser assembly which is convenient for manufacturing, while maintaining vibration damping within acceptable levels, thereby reducing the manufacturing costs thereof. Other features and advantages of the present invention will be better understood with reference to the preferred embodiment described hereinafter. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     Reference will now be made to the accompanying drawings in which:  
         [0010]      FIG. 1  is a schematic cross-sectional view of a turbofan gas turbine engine showing an exemplary application of the present invention;  
         [0011]      FIG. 2  is a partial cross-sectional view of a compressor diffuser assembly used in the engine of  FIG. 1 ;  
         [0012]      FIG. 3  is a partial cross-sectional view of an annular diffuser body of the compressor diffuser assembly of  FIG. 2 ;  
         [0013]      FIG. 4  is a cross-sectional view of a damper member used in the compressor diffuser assembly of  FIG. 2 ;  
         [0014]      FIG. 5  is a perspective view of a diffuser pipe used in the compressor diffuser assembly of  FIG. 2 ; and  
         [0015]      FIG. 6  is an enlarged cross-sectional view of an end portion of the diffuser pipe, as shown in the circled area  6  in  FIG. 5 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]     Referring to  FIG. 1 , a turbofan gas turbine engine incorporates an embodiment of the present invention, presented as an example of the application of the present invention, and includes a housing or a nacelle  10  which contains a fan section  12  and at least a major section of a core engine  14 . The core engine  14  comprises in flow series, a compressor section  16 , a combustion section  18 , a turbine section  20 , and an exhaust section  22 . The turbine section  20  and the compressor section  16  comprise multiple stages. At least one turbine (not indicated) within the turbine section  20  is rotationally connected to the final stage of the compressor section  16  by a shaft  24 .  
         [0017]     The final stage of the compressor section  16  is a rotating impeller  26  in flow communication with combustion section  18  through a diffuser assembly  28 . The impeller  26  draws air axially, and rotation of the impeller  26  increases the velocity of the air flow as the input air is directed over impeller vanes, to flow in a radially outward direction under centrifugal forces. In order to redirect the radial flow of air exiting the impeller  26  to an annular axial flow for presentation to a combustor  30 , the diffuser assembly  28  is provided. The diffuser assembly  28  also reduces the velocity and increases the static pressure of the air flow when the air flow is directed therethrough.  
         [0018]     Referring to  FIGS. 1-3 , the compressor diffuser assembly  28  includes an annular diffuser body  32  which is a machined ring having a plurality of orifices  34  disposed circumferentially spaced apart in an outer periphery  36  thereof, and extending inwardly and tangentially through the annular diffuser body  32 . Each of the orifices  34  is intersected by two adjacent orifices  34  in an asymmetrical configuration (only one adjacent orifice is shown). With such a configuration, the annular diffuser body  32  is positioned to surround a periphery of the impeller  26  for capturing the pressure air flow and directing same radially and outwardly through the tangential orifices  34 .  
         [0019]     The compressor diffuser assembly  28  further includes a plurality of diffuser pipes  38  inserted at one end  40  thereof into the individual orifices  34  of the annular diffuser body  32 . Each of the diffuser pipes  38  has a cross-section expanding rearwardly towards a second end thereof, which is generally referred to as “fishtail” pipes (see  FIG. 5 ). The diffuser pips  38  further direct the pressure air flow from the individual tangential orifices  34  through the rearwardly expanding cross-section, thereby discharging the pressure air flow to the combustion section  18  at a low velocity and high pressure.  
         [0020]     All orifices  34  and diffuser pipes  38  are identical, respectively, and therefore only one orifice and one diffuser pipe will be described in detail for convenience of the description.” 
         [0021]     Referring to  FIGS. 2-6 , the orifice  34  of the annular diffuser body  32  includes a counter-bore  42  which is an enlarged section of the orifice  34  at the orifice entry, thereby forming a substantially right angled step on the interface  44  between the enlarged entry section and the remaining section of the orifice  34 .  
         [0022]     The diffuser pipe  38  includes an end section  46  defining the end  40  and having a substantially cylindrical profile or a slightly rearwardly expanding round cross-section, as is more clearly shown in  FIG. 6 .  
         [0023]     The remaining section  48  of the diffuser pipe  38  has a curved profile for directing the air flow passing therethrough from a radial direction to a substantially axial direction. The curved remaining section  48  of the diffuser pipe has a cross-section expanding rearwardly towards the distal end thereof (not indicated), but only in one dimension of the cross-section such that the remaining section  48  of the diffuser pipe  38  represents a curved fishtail profile as more clearly shown in  FIG. 5 . The end section  46  has an outer diameter smaller than the inner diameter of the counter-bore  42 , thereby providing an annular space (not indicated) for accommodating a damper member  50  therebetween when the end  40  of the diffuser pipe  38  is inserted into the counter-bore  42 .  
         [0024]     The damper member  50  in this embodiment of the present invention is a ‘marcelled expander’, a metal wave spring having an irregular and discontinued ring profile in cross-section, as shown in  FIG. 4 . The damper member  50  disposed between the end section  46  of the diffuser pipe  38  and the counter-bore  42  of the orifice  34 , is forced into a resilient deformation condition which results in frictional forces being applied to the respective outer surface of the end section  46  of the diffuser pipe  38  and the inner surface of the counter-bore  42  of the orifice  34 . The frictional forces caused by the damper member  50  thus provides a snug attachment of the diffuser pipe  38  to the orifice  34  of the annular diffuser body  32 . Nevertheless, other than a marcelled expander, a damper member of other types can be alternatively used for the present invention, provided that the alternatively used damper members of other types are suitable for working in a relatively high temperature and high pressure of the high pressure compressor air. Examples are waves springs of other types, other spring types and other dampers made of resilient materials, and so on.  
         [0025]     The end section  46  of the diffuser pipe  38  preferably includes a rim  52  protruding radially therefrom at the end  40 . Preferably, a flange  54  extends radially and outwardly from the end section  46  of the diffuser pipe  38 , and is spaced apart from the rim  52  such that the damper member  50  can be retained around the end section  46  between the rim  52  and the flange  54  before the end section  46  of the diffuser pipe  38  is inserted into the counter-bore  42  of the orifice  34 .  
         [0026]     The rim  52  should have an outer diameter not greater than the inner diameter of the counter-bore  42  of the orifice  34 , and the flange  54  preferably has an outer diameter greater than the inner diameter of the counter-bore  42  of the orifice  34 . Therefore, the rim  52  is received within the counter-bore  42  of the orifice  34  while the flange  54  is positioned outside of the counter-bore  42  when the end section  46  of the diffuser pipe  38  is inserted into the counter-bore  42  of the orifice  34 .  
         [0027]     The space between the rim  52  and flange  54  is determined such that the end  40  of the diffuser pipe  38  abuts the interface  44  between the counter-bore  42  and the remaining section of the orifice  34  while the flange  54  abuts the flat surface defining the entry of the counter-bore  42 . Alternatively, the depth of the counter-bore  42  should be slightly greater than the distance between the front surface of the flange  54  and the end  40  of the diffuser pipe  38  such that the flange  54  can substantially seal the entry of the counter-bore  42  without interference when the end  40  of the diffuser pipe  38  is inserted into the counter-bore  42  of the orifice  34 .  
         [0028]     The rim  52  is preferably beveled on the front surface, as shown in  FIG. 6  for convenience of receiving the damper member  50  when the damper member  50  is forced to pass thereover in order to be attached to the end section  46  of the diffuser pipe  38  between the rim  52  and the flange  54 , prior to insertion of the end  40  of the diffuser pipe  38  into the counter-bore  42  of the orifice  34 . For convenience of insertion of the end  40  of the diffuser pipe  38  together with the attached damper member  50 , into the counter-bore  42  of the orifice  34 , the counter-bore  42  is preferably beveled at the entry thereof.  
         [0029]     Although it is preferable to attach the damper member  50  to the end section  46  of the diffuser pipe  38  prior to the insertion of the end  40  of the diffuser pipe  38  into the counter-bore  42  of the orifice  34 , the damper member  50  can alternatively be forced into the counter-bore  42  of the orifice  34  prior to the insertion of the end  40  of the diffuser pipe  38  into the counter-bore  42  of the orifice  34 .  
         [0030]     Because of the employment of damper member  50 , the manufacturing tolerances for both the counter-bore  42  in the annular body  32  and the end section  46  are not necessarily limited to a very accurate range, which results in time savings and thus cost savings during manufacture of the diffuser assembly. The damper members  50  provide a tighter or more snug attachment of the diffuser pipes  38  to the annular diffuser body  32  which is damps vibration to acceptable levels to provide good engine reliability.  
         [0031]     Modifications and improvements to the above-described embodiment of the present invention may become apparent to those skilled in the art. This invention is not only applicable to turbofan gas turbine engines, but is also applicable to other gas turbine engines in which such a diffuser assembly is equipped. The pipe diffuser need not have the configuration shown, and the present invention may be used with an suitable diffuser configuration. The foregoing description is therefore intended to be exemplary rather than limiting and the scope of the present invention is to be limited solely by the scope of the appended claims.