Rotary kinetic fluid motors or pumps – Working fluid passage or distributing means associated with... – Plural distributing means immediately upstream of runner
Reexamination Certificate
2000-04-03
2002-05-28
Lopez, F. Daniel (Department: 3745)
Rotary kinetic fluid motors or pumps
Working fluid passage or distributing means associated with...
Plural distributing means immediately upstream of runner
C415S200000, C416S24100B, C416S21300R
Reexamination Certificate
active
06394750
ABSTRACT:
TECHNICAL FIELD
This invention relates to the field of axial flow rotary machines and more particularly to a method and detail for processing, modifying or repairing a stator vane.
BACKGROUND OF THE INVENTION
FIG. 1
shows an axial flow rotary machine
10
of the turbofan, gas turbine engine type. The engine includes a compression section
12
, a combustion section
14
, and a turbine section
16
which are disposed an axis A. An annular flowpath
18
for working medium gases extends through the sections of the engine. The annular flowpath is the primary flowpath for the turbofan engine.
The working medium gases are compressed in the compression section
12
. The compressed gases are mixed with fuel in the combustion section
14
and burned to add energy to the gases. The hot pressurized gases are expanded through the turbine section
16
to produce useful work and are discharged from the engine to produce thrust.
As shown in FIG.
1
and
FIG. 2
, the engine is provided with a rotor assembly
22
In the turbine section
16
. The rotor assembly includes a rotor disk
24
and arrays of rotor blades which extend outwardly across the working medium flowpath, as represented by the arrays of rotor blades
26
. The rotor assembly extracts energy from the gases as the gases are passed through the turbine section. The rotor assembly transfers this energy to the compression section
14
to compress the incoming working medium gases.
A stator assembly
28
extends circumferentially about the rotor assembly
22
. The stator assembly supports the rotor assembly and includes a pressure vessel, as represented by the outer case
32
, to confine the working medium gases to the working medium flowpath. In many embodiments, the outer case also provides a support structure for components which bound the working medium flowpath. The stator assembly includes arrays of stator vanes
34
interdigitated with the arrays of rotor blades. Each array of stator vanes is disposed about the axis A.
As shown in
FIG. 2
, each stator vane
34
extends circumferentially with respect to the axis A. Each stator vane typically has an inner platform
36
and an outer platform
38
. The stator vane has an upstream end
42
and a downstream end
44
. These ends are also called respectively the leading edge and the trailing edge of the stator vane. An upstream leg
46
and a downstream leg
48
extend radially from the outer platform. Each leg has a foot, as represented by the upstream foot
52
and by the downstream foot
54
. Each foot adapts the leg to engage the outer case. One or more airfoils
56
extend radially across the working medium flowpath between the inner platform and the outer platform. The term “stator vane” includes constructions which have one airfoil or several airfoils. Stator vane constructions having several airfoils are frequently called “stator vane clusters”.
The airfoil
56
of the stator vane extends spanwisely and has a pressure side
58
and a suction side
62
(shown in FIG.
3
). The sides guide the working medium gases as the gases exit one array of rotor blades and enter a downstream array of rotor blades. The working medium gases push against and buffet the airfoil exerting both steady and unsteady aerodynamic forces on the airfoil. These forces are in part the result of wakes from the upstream rotor blades and bow waves from downstream rotor blades. In addition, heat is transferred from the hot working medium gases to the stator vane
34
and particularly to the airfoils
56
. The heat causes thermal gradients in the stator vane. The thermal gradients are aggravated by circumferential variations in temperature of the working medium gases in the flowpath. These variations in temperature result from variations in upstream operating conditions at the combustion section
14
of the engine.
The aerodynamic and thermal forces cause cyclic stresses in the stator vane
34
and may cause cracking of the stator vane, for example, at those locations on the airfoil
56
that are subjected to high repetitive stresses. The leading edge
64
of the airfoil
56
is one location on the stator vane that is particularly vulnerable to cracking. This occurs because the airfoil is a structural beam that has a very narrow outermost fiber, that is, the relatively narrow leading edge
64
. The narrow leading edge of the beam has an associated high stress concentration factor. The effect of this high stress concentration factor is aggravated by the change in geometry at the location where the airfoil (or structural beam) transitions into the outer platform
38
and is referred to as the region or junction T. This is usually the tangency point between the airfoil fillet and the airfoil.
FIG. 3
is a perspective view of three stator vanes
34
. Each stator vane has three airfoils
56
.
FIG. 4
is a cross-sectional view of the pressure side airfoil
56
with part of the airfoil broken away. As shown in FIG.
3
and
FIG. 4
, cracking of the pressure side airfoil
56
frequently occurs in the leading edge
64
at the junction T, that is, the transition from the leading edge of the airfoil to the platform. With time, the crack will grow rearwardly from the leading edge and may lead to destructive failure of the stator vane. Depending on its circumferential location in the annular flowpath
18
with respect to upstream operating conditions, the stator vane may not have a cracked pressure side airfoil as shown. Instead or in addition to the pressure side airfoil, the central airfoil or suction side airfoil may crack at the leading edge. Typically, none of these stator vanes are repairable by welding or bonding repairs, such as by using diffusion bonding filler, because of the high stress concentration factors acting at the transition of the leading edge to the platform.
One approach is to replace damaged stator vanes with redesigned stator vanes.
FIG. 5
is a schematic, side elevation view of a redesigned stator vane
34
r
which is partially in section and partially broken away. The redesigned stator vane has a leg
46
r
having an axial thickness or axial length D. This thickness is uniform for the entire circumferential extent of the redesigned stator vane. The thickness of the redesigned stator vane is thicker or longer in the axial direction than the thickness or axial length D of the upstream leg
46
shown in FIG.
3
and FIG.
4
. The redesigned stator vane
34
r
has a local opening or local pocket
66
at each airfoil
56
r
which extends rearwardly from the upstream end
42
of the stator vane. The opening is circumferentially and axially aligned with the leading edge
64
r
of the airfoil. The opening interrupts the radial continuity of the stator vane and the radial continuity of the load path from the airfoil leading edge to the leg and thence to the support structure. This causes the load path to shift rearwardly. The high gas loads acting on the airfoil are not passed by the stator vane through the leading edge region next to the platform. This avoids subjecting the loads to the high stress concentration factor caused by the narrow leading edge and the transition geometry. As a result, the stator vane has an increased fatigue life. However, replacing an earlier version of the stator vane that is cracked or expected to crack with a redesigned stator vane requires the purchase of a new stator vane.
Accordingly, scientists and engineers working under the direction of applicants assignee have sought to develop a method for processing a stator vane which has a crack or which might crack in a critical location such as the transition zone from the leading edge to the platform.
SUMMARY OF INVENTION
This invention is in part predicated on the recognition that earlier version stator vanes may be modified or repaired by shifting the diffusion bonding surfaces for a replacement detail away from the leading edge to platform transition and its high concentration stress factor and forming a replacement detail having entirely new material at the junction T between the leading edge and the platform. Such a repl
Fleischhauer Gene D.
United Technologies Corporation
Woo Richard
LandOfFree
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