Turbine including a thermal growth accommodating mount for a vane assembly

Unequal flow rates of dilution air about an annular combustor and the resulting hot spots and thermal stresses are avoided in a structure wherein a vane assembly (66) made up of ring (76) and integral vanes (76) is mounted to the rear turbine shroud (42) for limited movement with respect thereto sufficient to accommodate unequal thermal growth of the rear turbine shroud (42) and the vane assembly (66).

FIELD OF THE INVENTION 
This invention relates to gas turbines, and more particularly, to the 
mounting of a vane assembly to a turbine wheel shroud such that unequal 
rates of thermal growth may be accommodated. 
BACKGROUND OF THE INVENTION 
In the commonly assigned application of Shekleton et al, filed Dec. 28, 
1988, entitled Gas Turbine Annular Combustor with Radial Dilution Air 
Injection, Ser. No. 291,041 and assigned to the same assignee as the 
instant application, the details of which are herein incorporated by 
reference, there is disclosed a gas turbine construction wherein the vast 
majority of dilution air is passed completely around an annular combustor 
to cool the same and to impinge upon a turbine wheel shroud to likewise 
provide cooling. The dilution air is then injected into the combustor 
outlet just upstream of the turbine nozzle to mix with the gases of 
combustion before contacting the nozzle. An extremely compact assembly 
results. Moreover, the assembly is capable of relatively high power 
densities without accelerated failure rates because of the excellent 
cooling of the turbine shroud that is obtained which in turn reduces 
thermal stresses in the apparatus. 
Nonetheless, further improvement is desired so as to achieve the maximum 
utility of the system. In particular, for maximum utility, such a system 
must have uniform airflow about the combustor. Typically, the airflow will 
be from the turbine compressor about the radially outer side of the 
annular combustor and then about a radial wall of the combustor opposite 
from the combustor outlet and finally, about the radially inner wall of 
the combustor whereat the dilution air further impacts against the turbine 
shroud. If this airflow is not uniform, hot spots may develop. Hot spots 
are, of course, to be avoided because the resulting thermal gradients 
induce thermal stresses due to the temperature differences. 
In a system of the type mentioned, it is extremely important that uniform 
airflow be present in the area adjacent the turbine shroud and where the 
dilution air stream is combined with the gases of combustion just upstream 
of the nozzle. Not infrequently, vanes will be employed in this area to 
direct the flow of the dilution area in a given path and if flow through 
the vanes is not uniform, hot spots will result. These in turn will result 
in distortions that may further change the shape of the passage for the 
airflow, which in turn increases the nonuniformity of airflow, which leads 
to greater distortions, etc. 
The present invention is directed to overcoming one of more of the above 
problems. 
SUMMARY OF THE INVENTION 
The principal object of the invention is to provide a new and improved gas 
turbine. More specifically, it is an object of the invention to provide, 
in a gas turbine, a new and improved means for mounting a vane structure 
in a dilution air path so as to achieve uniform flow of dilution air and 
thereby avoid the difficulties associated with non-uniform flow. 
An exemplary embodiment of the invention achieves the foregoing object in a 
gas turbine structure including a turbine wheel mounted for rotation about 
an axis and with a shroud about the turbine wheel. An annular combustor is 
disposed about the shroud and is spaced therefrom to define a cooling air 
passage. The combustor discharges gas towards the turbine wheel for 
driving the same. According to the invention, a vane assembly is located 
in the cooling air passage and is mounted on the shroud for limited 
movement relative thereto to allow unequal thermal growth between the 
shroud and the vane assembly. 
As a consequence of this construction, distortions as a result of unequal 
thermal growth are eliminated so that uniform flow passage size may be 
achieved to minimize or eliminate the formation of hot spots. 
In a preferred embodiment, a cooling air port is at the end of the cooling 
air passage and is defined by the space between the shroud and the 
combustor just upstream of a nozzle utilized to direct gases at the 
turbine. The invention provides a vane assembly in the port which in turn 
has vanes extending generally axially across the port into substantial 
abutment with the combustor. 
According to this embodiment of the invention a mounting ring is located on 
the shroud and defines a radially directed, annular vane assembly 
receiving groove. A vane assembly is located in the groove and only 
partially fills the same so that relative movement between the vane 
assembly and the shroud may occur to relieve thermal stresses. 
In a highly preferred embodiment of the invention, the shroud includes an 
annular, shallow groove having a planar bottom opposite of the turbine 
wheel and facing the port. The groove has a width of sufficient size so as 
to loosely receive the vane assembly and allow unequal thermal growth of 
the shroud and the vane assembly. 
Preferably, a retaining ring is mounted on the shroud and partially 
overlies the groove to capture the vane assembly therein. 
In a preferred embodiment, the vane assembly is made up of a ring mounting 
a plurality of vanes. 
In a highly preferred embodiment, the ring and the vanes are internally 
formed of a single piece of material According to the invention, the vanes 
may be defined by a series of spaced grooves machined in a side of the 
ring. 
According to one embodiment of the invention, the vanes extend across the 
port to contact with the combustor. Typically, they will be butt fused to 
the combustor as by brazing. 
According to another embodiment of the invention, the combustor, adjacent 
the port, includes vane receiving openings and the vanes are located 
within the openings and are fused to the combustor within such openings. 
Other objects and advantages will become apparent from the following 
specification taken in connection with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An exemplary embodiment of the gas turbine engine employing the invention 
is illustrated in FIG. 1 and with reference thereto is seen to include a 
rotor, generally designated 10, mounted by any suitable means (not shown) 
for rotation about an axis 12. As is well known, the rotor includes a hub 
14. On one side of the hub 14, there may be provided vanes or blades 16 
against which hot gases of combustion may be directed to rotate the rotor 
10 about the axis 12. Thus, that section of the hub 14 with the blades 16 
defines a turbine wheel. 
Oppositely of the blades 16, the hub 14 may include compressor vanes 18 if 
desired. Alternatively, a separate hub may be utilized to define the 
compressor. For that matter, the compressor defining hub need even not be 
mounted for rotation about the axis 12 but may rotate about another axis. 
In any event, compressed air from the compressor blades 18 is passed 
through a diffuser 20 as illustrated by arrows 22. From the diffuser 22 
the air passes into a housing 24 that is in surrounding relationship to 
the rotor 10 as well as a so called front shroud 26 for the turbine wheel 
defined go the hub 14 and the blades 16. Contained within the housing 24 
is a so-called annular combustor 28 having a radially outer wall 30, a 
generally radial wall 32, and a radially inner wall 34. Within the walls, 
30, 32, 34, a somewhat annular or ringlike combustion space 36 is defined. 
The space 36 includes an outlet area 38 immediately upstream of a 
plurality of vanes or blades 40 located between the front shroud 26 and a 
rear shroud 42 to define a nozzle to direct the gases of combustion in the 
direction of an arrow 44 against the blades 16 to drive the rotor 10. As 
is well known, the rear shroud 42 extends from the nozzle 40 along the 
periphery of the blades 16 to the end of the rotor 10 to contain the gases 
of combustion against the blades 16. 
As can be seen, the spacing of the walls, 30, 32 from the housing 24 
provides a cooling air plenum about the annular combustor 28. This cooling 
air plenum is continued in the vicinity of the rear shroud 42 and is 
designated 50. The plenum terminates in an annular port 52 just upstream 
of the outlet 38 from the combustor 28 to the nozzle vanes 40. Various 
inlets such as shown at 54, 56, 58 and 60 are provided to allow a certain 
amount of dilution or cooling air to exit the plenum and enter the 
combustor for cooling purposes. However, the same are sized so that the 
vast majority of cooling air passes entirely about the combustor 28 to 
enter the combustor at the port 52 as more fully disclosed in the 
previously-identified application of Shekleton et al. 
One or more fuel injectors 64 are mounted on the housing 24 and extend into 
the combustor space 36. The same may inject fuel tangentially to allow 
fabrication of a relatively short (in the axial direction) annular 
combustor 28. Typically, there will be considerable circumferential swirl 
of the gases as a result and it will be desirable that the dilution air 
entering the combustor at the port 52 be swirling in the same direction. 
Consequentially, if a vane assembly, generally designated 66, is disposed 
within the port to provide for such swirling action and to assure 
uniformity of flow at the port. 
Turning now to FIGS. 2 and 3, near its radially outer terminus 68, the rear 
shroud 42 includes a shallow, peripheral groove 70 having a planar bottom 
72 that faces away from the nozzle vanes 40 and toward the annular 
combustor 28. Disposed within the groove 70 is a ring 74 which mounts a 
plurality of axially extending vanes 76. The vanes 76 extend away from the 
rear shroud 42 toward the combustor 28 and abut the same period. 
Preferably, the ends 78 of the vanes 76 are butt brazed to the combustor 
at this location. 
It will observed that the width of the groove 70 is greater than the width 
or thickness of the ring 74. It will also be observed that the ring 74 
includes a planar surface 80 that is in abutment with the planar bottom 72 
of the groove 70. As a consequence of this construction, the ring 74 may 
slide slightly within the groove 70 as a result of unequal thermal growth 
of the shroud 42 and the ring 74. 
To captivate the ring 74 within the groove 70 a retaining or mounting ring 
82 is secured to the end 68 of the shroud 42 to partially overlay the 
radially outer extremity in abutting relation to a peripheral lip 84 that 
is directed radially outwardly and is on the ring 74. 
It will be noted that this construction defines a radially directed groove 
86, here radially inwardly opening. The groove 86 is partially occupied by 
the ring 74 but not fully occupied or filled thereby so as to allow the 
aforementioned differential thermal growth of the various components. 
As can be seen in FIG. 3, the vanes 76 are arcuate in configuration 
Preferably, they are formed by machining rather wide but relatively 
shallow grooves 90 in the side of the ring opposite the surface 80. Thus, 
the vane assembly in a preferred embodiment includes the vanes 78 that are 
integral with the ring 74, being formed a single piece of material. 
A modified embodiment of the invention is illustrated in FIG. 4. According 
to this embodiment of the invention, a wall 100 of the combustor 28 is 
provided with a series of openings 102 sized and shaped and aligned with 
the ends 104 of the the vanes 76. As a consequence, the ends 104 of the 
vane 76 may be introduced into the openings 102 and may be inset fused 
thereto as, for example, by brazing. This embodiment of the invention 
produces a stronger bond between the vane 76 and the combustor 28 but is 
somewhat more complicated to form. 
From the foregoing, it will be appreciated that the vane assembly of the 
invention is ideally mounted in such a way that variations or differences 
in thermal growth between the rear shroud 42 and vane assembly 66 are 
readily accommodated. Moreover, because the vane assembly 66 is mounted to 
the shroud rear 42 and bonded to the combustor 28, which is thinner than 
the rear shroud 42 the latter relatively easily follows the former upon 
thermal growth such that the size of the dilution air passages between the 
vanes 76 does not change during operation of the turbine and thereby 
prevents the formation of hot spots. This in turn assures a minimum of 
thermal stress and promotes long life of the turbine engine