Patent Application
20140178187
The present invention relates generally to gas turbine technology and, more specifically, to the design of a gas turbine diffuser exhaust frame.
A gas turbine engine is conventionally configured to receive ambient air and to discharge exhaust or combustion gases into an annular diffuser. The combustion gases are then discharged to atmosphere through a conventional exhaust stack.
The engine may take any conventional form including single or dual rotor engines, with one or more compressors, followed in turn by a combustor, (or an annular array of combustors) in which compressed air is mixed with fuel and ignited for generating the combustion or exhaust gases. Disposed downstream of the one or more combustors are one or more turbine stages which extract energy from the exhaust gases for powering the engine as well as typically providing output power through an output shaft for a load such as a generator.
The diffuser or exhaust frame typically includes an annular frame having an inner annular wall spaced radially inwardly from an outer annular wall or casing which define radially therebetween an annular flow channel for channeling the combustion gases to the diffuser and exhaust stack. The frame also typically includes a plurality of circumferentially-spaced and aligned, radially-extending struts disposed between the inner and outer annular casings.
In current gas turbine exhaust frame designs, a single row of rectangular struts are used to transfer loads from the inner to the outer annular members. The shape of each strut, and its cross-sectional area, are governed by the shape of an airfoil that surrounds the strut, and the total load to be transferred. In this type of configuration, the airfoils are relatively long, thereby producing larger losses, especially during part-load operating conditions.
It would therefore be desirable to have a strut/airfoil arrangement which enables smaller cross-sectional areas, and which produces smaller performance losses especially at part-load conditions.
In one exemplary but nonlimiting embodiment, the invention provides a gas turbine exhaust frame comprising an inner substantially cylindrical wall; an outer substantially cylindrical wall establishing an annular exhaust gas flow path therebetween; and a plurality of airfoils extending radially between the inner wall and the outer wall, the plurality of airfoils arranged in first and second axially-spaced, circumferentially-staggered rows.
In another exemplary aspect, the invention provides a gas turbine exhaust diffuser comprising a frame having an inner substantially cylindrical wall and an outer substantially cylindrical wall defining an annular exhaust gas flow channel; and a plurality of airfoils extending between the inner and outer walls, the plurality of airfoils arranged in first and second axially-spaced, circumferentially-staggered rows, wherein the first and second axially-spaced, circumferentially-staggered rows at least partially overlap in an axial direction.
In still another aspect the invention a gas turbine exhaust diffuser comprising a frame having an inner substantially cylindrical wall and an outer substantially cylindrical wall defining an annular exhaust gas flow channel; a plurality of airfoils extending between the inner and outer walls, the plurality of airfoils arranged in first and second annular, axially-spaced and circumferentially-staggered rows; each of the plurality of airfoils having a leading edge and a trailing edge and a slot extending radially along and adjacent at least a portion of the leading edge, the slot having an inlet on one side of the airfoil extending angularly in a downstream direction to an outlet on an opposite side of the airfoil.
The invention will now be described in greater detail in connection with the drawings identified below.
Illustrated schematically in
Typically, the engine 10 may be a single or dual rotor engine, with one or more compressors and a combustor (not shown) in which compressed air is mixed with fuel and ignited for generating the combustion or exhaust gases 14. Disposed downstream of the combustor(s) are one or more turbine stages (not shown) which extract energy from the exhaust gases 14 for powering the engine 10 as well as for providing output power through an output shaft 20. The engine 10 and the diffuser 16 are typically axis-symmetrical about a centerline axis 22.
The diffuser 16 illustrated in
The inner wall 26 and the outer wall 28 are substantially cylindrical bodies, and it will be understood that the outer wall or casing 28 may taper along its length, typically outwardly in the direction of exhaust gas flow.
Typically, the strut or airfoil is constructed in two pieces including an internal structural strut component 32 (see also.
With reference to
In the exemplary but nonlimiting embodiment, the first and second rows 42, 44 of airfoils 36 are staggered in the circumferential direction. In other words, in a circumferential direction, the airfoils are alternately located in the two respective rows. In the axial direction, the rows 42, 44 may be completely axially-spaced or partially overlapped as shown in
In the exemplary but nonlimiting embodiment, a 50% axial overlap has been shown to improve diffuser/exhaust frame performance but the degree of overlap may be tailored to provide optimum performance based on specific applications.
In this exemplary but nonlimiting configuration, one or more of the airfoils 36 in one or both of the two rows 42, 44 is provided with an elongated slot 54 adjacent the respective leading edge 50, and extending radially between the root end and the tip end. The radial height of the slot is variable, recognizing that adequate space must be maintained for securing the airfoils to the inner and outer walls. As best seen in
With this arrangement, total load coming onto the struts is divided on the two rows 42, 44 of airfoils 36. This permits each internal strut to have a smaller cross-section than in the prior single-row design. Specifically, the arrangement permits both a smaller axial length and a smaller width for the internal struts 35 (
As best seen in
While various embodiments are described herein, it will be appreciated from the specification that various combinations of elements, variations or improvements therein may be made by those skilled in the art, and are within 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 essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
