Patent Application
20120020779
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.
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.
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.
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.
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.
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.
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.
