Rotary kinetic fluid motors or pumps – With passage in blade – vane – shaft or rotary distributor...
Reexamination Certificate
2000-04-05
2001-12-18
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
With passage in blade, vane, shaft or rotary distributor...
C415S116000, C415S176000
Reexamination Certificate
active
06331096
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to impingement cooling of a gas turbine nozzle band undercut region and particularly relates to impingement cooling of the nozzle band edge in a design where the weld joint between the nozzle segment cover and the nozzle wall is remote from the nozzle wall exposed to the hot gas path.
In current gas turbine designs, nozzle segments are typically arranged in an annular array about the rotary axis of the turbine. The array of segments forms outer and inner annular bands and a plurality of vanes extend between the bands. The bands and vanes define in part the hot gas path through the gas turbine. Each nozzle segment comprises an outer band portion and an inner band portion and one or more nozzle vanes extend between the outer and inner band portions. In current gas turbine designs, a cooling medium, for example, steam, is supplied to each of the nozzle segments. To accommodate the steam cooling, each band portion includes a nozzle wall in part defining the hot gas path through the turbine, a cover radially spaced from the nozzle wall defining a chamber therewith and an impingement plate disposed in the chamber. The impingement plate defines with the cover a first cavity on one side thereof for receiving cooling steam from a cooling steam inlet. The impingement plate also defines, along an opposite side thereof and with the nozzle wall, a second cavity. The impingement plate has a plurality of apertures for flowing the cooling steam from the first cavity into the second cavity for impingement cooling the nozzle wall. The cooling steam then flows radially inwardly through cavities in the vane(s), certain of which include inserts with apertures for impingement cooling the side walls of the vane. The cooling steam then enters a chamber in the inner band portion and reverses its flow direction for flow radially outwardly through an impingement plate for impingement cooling the nozzle wall of the inner band. The spent cooling medium flows back through a cavity in the vane to an exhaust port of the nozzle segment.
The cover provided each of the outer and inner band portions is preferably welded to the corresponding nozzle wall. In prior designs, the weld joint between the cover and the nozzle wall was disposed at a radial location between the nozzle wall and the spline seal between side walls of adjacent nozzle segments. In that location, the weld was exposed to the high temperature gases in the hot gas flow path and was very difficult to cool. Thus, weld joint fatigue life was significantly reduced due to its proximity to the hot gas path. Moreover, the location of the weld was not optimum for manufacturing repeatability and was very sensitive to manufacturing tolerances. The weld joint was characterized by variable wall thicknesses which increased the stress at the joint, decreased the low cycle fatigue and limited the life of the parts. The wall thickness at the weld after machining was also a variable which could not be tolerated in the manufacturing process.
BRIEF SUMMARY OF THE INVENTION
In accordance with a preferred embodiment of the present invention, a cooling system is provided in a nozzle segment design in which the weld joint between the cover and nozzle wall is on the side of the spline seal remote from the nozzle wall exposed to the hot gas path. That is, the weld joint between the cover and the nozzle wall of the outer band is located radially outwardly of the spline seal between adjacent outer bands while the weld joint between the cover and the nozzle wall of the inner band is located radially inwardly of the spline seal between adjacent inner bands. This reduces the temperature of the weld joints during turbine operation, reduces the stresses across the joints, both thermal and mechanical, eliminates any requirement for machining after welding and results in joints of constant thickness and higher fatigue life. The location also leads to improved machinability and tolerance to weld defects.
To provide that weld location, undercut regions adjacent the side walls of the nozzle segment bands are formed. Particularly, each undercut region includes a side wall or edge of the nozzle segment and an inturned flange extending inwardly from and generally parallel to the nozzle wall and spaced from the nozzle wall. Cooling the nozzle band side wall or edge, however, is quite difficult in view of the undercut region which spaces the side wall or edge a substantial distance from the impingement plate which, in turn, reduces the effectiveness of impingement cooling the segment side wall.
In accordance with the present invention, improved side wall fabrication and cooling is provided. Particularly, with the weld joint between the cover and the nozzle wall located remotely from the hot gas path through the turbine, side wall cooling is improved by providing impingement cooling apertures directly through the inturned flanges of the side walls of the bands, e.g., through the castings forming the bands, in order to reduce the distance traveled by the cooling steam flow. Thus, after the interface for the securement of the impingement plate is machined into the nozzle side wall, impingement apertures may be formed through the inturned flange. Subsequently, the impingement plate is welded to the inturned flange to define the cavities or plenums on opposite sides of the impingement plate. Impingement cooling of the nozzle side wall and in the undercut region is thus provided by flowing the cooling medium through apertures in both the impingement plate and the inturned flange.
In a preferred embodiment according to the present invention, there is provided for use in a gas turbine, a nozzle segment having outer and inner bands and at least one vane extending between the bands, at least one of the bands including a nozzle wall defining in part a hot gas path through the turbine, a cover radially spaced from the nozzle wall defining a chamber therebetween and an impingement plate secured within the segment and disposed in the chamber to define with the cover a first cavity on one side thereof for receiving a cooling medium, the impingement plate on an opposite side thereof from the first cavity defining with the nozzle wall a second cavity, the impingement plate having a plurality of apertures therethrough for flowing the cooling medium from the first cavity into the second cavity for impingement cooling the nozzle wall, the nozzle segment including a side wall extending generally radially between the nozzle wall and the cover and having an inturned flange spaced from the nozzle wall, the inturned flange defining with the nozzle wall and the side wall an undercut region adjacent the side wall, and a plurality of apertures through the inturned flange for flowing the cooling medium from the first cavity for impingement cooling the side wall in the undercut region.
In a further preferred embodiment according to the present invention, there is provided in a gas turbine having a nozzle segment including outer and inner bands and at least one vane extending between the bands and wherein at least one of the bands includes a nozzle wall defining in part a hot gas path through the turbine, a cover radially spaced from the nozzle wall defining a chamber therebetween and an impingement plate secured within the band and disposed in the chamber to define with the cover a first cavity on one side thereof for receiving a cooling medium and a second cavity with the nozzle wall on an opposite side thereof, the impingement plate having a plurality of apertures therethrough for flowing the cooling medium from the first cavity into the second cavity for impingement cooling the nozzle wall, the nozzle segment including a side wall extending generally radially between the nozzle wall and the cover and having an inturned flange spaced from the nozzle wall with the nozzle wall and the side wall defining an undercut region adjacent the side wall, a method of cooling the side wall of the one band including flowing a cooling medium through a plurality of aperture
Burdgick Steven Sebastian
Itzel Gary Michael
General Electric Company
Look Edward K.
McAleenan James M
Nixon & Vanderhye
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