Patent Publication Number: US-8540484-B2

Title: Low mass diffuser vane

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of Contract No. N0019-06-C-0081 awarded by NAVAIR. 
    
    
     BACKGROUND 
     The present invention relates to diffusers, and in particular, to a wedge-type diffuser for use in gas turbine engines. In some gas turbine engines a diffuser is positioned downstream of a compressor impeller to receive compressed gas and reduce the flow velocity, thus converting kinetic energy of the compressed gas into static pressure. Such diffusers often have vanes for improving efficiency and reducing vortices. Using a vaned diffuser adds undesirable mass, and consequently weight, to the gas turbine engine. In applications where it is especially important to reduce weight, such as gas turbine engines used on aircraft, the additional mass of a vaned diffuser is especially undesirable. 
     SUMMARY 
     According to the present invention, a wedge-type diffuser includes a diffuser floor and a plurality of wedge-shaped vanes. The wedge-shaped vanes extend from the diffuser floor and have a top surface, a leading edge, and a trailing edge. Each of the wedge-shaped vanes has a slot extending from the trailing edge toward the leading edge. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a gas turbine engine. 
         FIG. 2  is a perspective view of the diffuser used in the gas turbine engine of  FIG. 1 . 
         FIG. 3  is a top view of the diffuser of  FIG. 2 . 
         FIG. 4A  is top view of a wedge-shaped vane of the diffuser shown in  FIGS. 2 and 3 . 
         FIG. 4B  is a top view of a second embodiment of the wedge-shaped vane of the diffuser shown in  FIGS. 2 and 3 . 
         FIG. 4C  is a top view of a third embodiment of the wedge-shaped vane of the diffuser shown in  FIGS. 2 and 3 . 
         FIG. 4D  is a top view of a fourth embodiment of the wedge-shaped vane of the diffuser shown in  FIGS. 2 and 3 . 
         FIG. 5  is a sectional view of the wedge-shaped vane taken along line  5 - 5  of  FIG. 4A . 
         FIG. 6  is a sectional view of the wedge-shaped vane taken along line  6 - 6  of  FIG. 4A . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a side view of gas turbine engine  10  having rotor assembly  12  which includes compressor impeller  14  connected to turbine  16  by impeller shaft  18  being threadedly engaged with tie bolt  20 . This allows for compressor impeller  14  to be driven by turbine  16  rotatably about centerline axis C L . Diffuser  22  is a wedge-type diffuser with wedge-shaped vanes  24  and straightener vanes  26  extending from diffuser floor  28 . Wedge-shaped vanes  24  extend from radially-extending inner platform  30  of diffuser floor  28 . Straightener vanes  26  extend from outer platform  32  of diffuser floor  28 , which extends longitudinally, substantially parallel to centerline axis C L . Diffuser  22  is connected to shroud  34  via bolts  36  extending through both diffuser  22  and shroud  34  such that wedge-shaped vanes  24  are positioned between shroud  34  and diffuser floor  28 . 
     Diffuser  22  is positioned along a gas flow path adjacent and downstream of compressor impeller  14  for receiving compressed gas, reducing the flow velocity of that compressed gas, and thus converting kinetic energy of the compressed gas into static pressure. Straightener vanes  26  reduce vortices that could otherwise blow out a flame in combustor  38 , which is positioned along the gas flow path adjacent and downstream of diffuser  22 . Turbine  16  is also positioned along the gas flow path, adjacent and downstream of combustor  38 , for extracting energy from high pressure gas received from combustor  38 . Turbine  16  transmits power via tie bolt  20  to impeller shaft  18 , which drives not only compressor  12  but also has spline  40  for transmitting power to a gearbox (not shown) for driving various components (not shown), such as a propeller, generator, hydraulic pump, other aircraft components, or even non-aircraft components. Seal plate  44  is adjacent diffuser floor  28  and provides a seal between compressor impeller  14  and turbine  16 . 
       FIG. 2  is a perspective view of diffuser  22 , showing tapered inner rim  46  of inner platform  30  which interfaces with compressor impeller  14  (shown in  FIG. 1 ). A plurality of bolt holes  48  extend through diffuser floor  28  and each of the plurality of wedge-shaped vanes  24 , for allowing bolts  36  (shown in  FIG. 1 ) to connect diffuser  22  to shroud  34  (shown in  FIG. 1 ). Alignment pins  50  align diffuser  22  with shroud  34  and the rest of gas turbine engine  10  (shown in  FIG. 1 ) about centerline axis C L  (shown in  FIG. 1 ). 
     Each wedge-shaped vane  24  has leading edge  52 , trailing edge  54 , pressure side surface  56 , suction side surface  58 , and top surface  60 . Trailing edge  54  is wider than leading edge  52 , and wedge-shaped vane  24  tapers substantially continuously from trailing edge  54  to leading edge  52 . Top surface  60  is defined between pressure side surface  56  and suction side surface  58 . Compressed gas from compressor impeller  14  flows along and between pressure side and suction side surfaces  56 ,  58  of adjacent wedge-shaped vanes  24  from leading edge  52  to trailing edge  54 . Flow velocity is reduced and static pressure is increased as the gas passes between each diverging pair of wedge-shaped vanes  24 . 
     Each wedge-shaped vane  24  has a slot  62  extending from trailing edge  54  toward leading edge  52 . In the illustrated embodiment, slot  62  extends along a portion of top surface  60 , from trailing edge  54  to bolt hole  48 , and along an entire length of trailing edge  54 , from top surface  60  to diffuser floor  28 . In the illustrated embodiment, slot  62  is substantially centered on trailing edge  54 , effectively forming two legs  64 ,  66  at trailing edge  54  that define slot  62 . In the illustrated embodiment, leg  64  is longer than leg  66 . Each respective leg  64 ,  66  has a substantially constant width along a portion of its length. 
     Slot  62  reduces the mass of each wedge-shaped vane  24 , and consequently, reduces the weight of the entire diffuser  22 . Because trailing edge  54  is wider than leading edge  52 , slot  62  can be added to trailing edge  54  without reducing the strength of wedge-shaped vanes  24  below a suitable threshold. Flow of gas through diffuser  22  can create an aerodynamic wake at trailing edge  54 . Slots  62  can be sized so as to have a negligible effect on aerodynamic wake created at each trailing edge  54  during operation of gas turbine engine  10 . The size of slots  62  can be selected by factoring requirements for strength, mass reduction, and gas flow. 
     Leading edge  52 , trailing edge  54 , pressure side surface  56 , and suction side surface  58  of each wedge-shaped vane  24  are connected to inner platform  30  of diffuser floor  28  at filleted interface  68 . Interface  68  is also filleted at slot  62 . Filleting can help improve strength characteristics of wedge-shaped vanes  24  at these locations. 
     Each straightener vane  26  has leading edge  70 , trailing edge  72 , suction side surface  74 , pressure side surface  76 , and outer surface  78 . Leading edge  70  of straightener vane  26  is positioned radially outward from trailing edge  54  of wedge-shaped vane  24 . Compressed gas from wedge-shaped vanes  24  flows along and between suction side and pressure side surfaces  74 ,  76  of adjacent straightener vanes  26  from leading edge  70  to trailing edge  72 . Curvature of suction side and pressure side surfaces  74 ,  76  straightens the gas flow to reduce vortices. 
     Diffuser  22  can be manufactured by first forming diffuser  22  with a plurality of wedge-shaped vanes  24  extending from diffuser floor  28  using casting, machining, or a combination of casting and machining. Diffuser  22  can be made of various materials, such as 15.5 steel, titanium, or aluminum, depending on application requirements. Next, slots  62  can be created by machining to remove material from each trailing edge  54  of each wedge-shaped vane  24 . In one embodiment, the material can be removed by first drilling bolt hole  48  in one of wedge-shaped vanes  24  and then cutting back from bolt hole  48  to trailing edge  54 . Cutting can be done in a single pass or can include multiple cutting passes. Alternatively, the material can be removed by cutting from trailing edge  54  in toward leading edge  52 , in single or multiple cutting passes. At some point of the process, some or all of interface  68 , including that at slot  62  and trailing edge  54 , can be filleted for improved strength. The resulting wedge-type diffuser  22  can be relatively light weight, reliable, and easy to manufacture. 
       FIG. 3  is a top view of diffuser  22 .  FIG. 3  shows each wedge-shaped vane  24  being substantially identical and arranged with rotational symmetry about centerline axis C L . Each wedge-shaped vane  24  is tilted with respect to centerline axis C L . 
       FIGS. 4A ,  4 B,  4 C, and  4 D are top views of alternative embodiments, each of a single illustrative example wedge-shaped vane  24 .  FIG. 4A  shows the embodiment of wedge-shaped vane  24  illustrated in  FIGS. 2 and 3 . Slot  62  extends from trailing edge  54  to bolt hole  48 . At bolt hole  48 , slot  62  has a width substantially equal to a diameter of bolt hole  48  and then gradually widens toward trailing edge  54 . 
       FIG. 4B  shows a second embodiment of wedge-shaped vane  24 , identified as wedge-shaped vane  224 . Slot  262  is similar to slot  62  (shown in  FIG. 4A ), except slot  262  has a width less than a diameter of bolt hole  248 . Thus, each leg  264 ,  266  of trailing edge  254  is wider than each respective leg  64 ,  66  (shown in  FIG. 4A ). 
       FIG. 4C  shows a third embodiment of wedge-shaped vane  24 , identified as wedge-shaped vane  324 . Slot  362  is similar to slot  62  (shown in  FIG. 4A ), except slot  362  extends from trailing edge  54  through bolt hole  348  toward leading edge  52 . Thus, each leg  364 ,  366  of trailing edge  354  is longer than each respective leg  64 ,  66  (shown in  FIG. 4A ). 
       FIG. 4D  shows a fourth embodiment of wedge-shaped vane  24 , identified as wedge-shaped vane  424 . Slot  462  is similar to slot  62  (shown in  FIG. 4A ), except slot  462  extends from trailing edge  54  toward bolt hole  448  and leading edge  52 , but stops short of bolt hole  448 . Thus, slot  462  is separated from bolt hole  448  by bridge portion  480  of wedge-shaped vane  424 , and each leg  464 ,  466  of trailing edge  454  is shorter than each respective leg  64 ,  66  (shown in  FIG. 4A ). 
     In further alternative embodiments, the dimensions of slots  62 ,  262 ,  362 , and  462  can be further varied so long as their shape and size are suitable for strength, gas flow, and mass requirements. 
       FIGS. 5 and 6  are sectional views of wedge-shaped vane  24  taken along lines  5 - 5  and  6 - 6 , respectively, of  FIG. 4A . These views show greater detail of the interior of slots  62  and bolt holes  48 . 
     While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed, but that the invention will include all embodiments falling within the scope of the appended claims. For example, diffuser  22  need not be limited to gas turbine engines for use on aircraft, but can be used on other applications that benefit from a wedge-type diffuser having relatively low mass vanes. Accordingly, diffuser  22  can be shaped for each particular application.