Rotary kinetic fluid motors or pumps – Bearing – seal – or liner between runner portion and static part – Between blade edge and static part
Reexamination Certificate
2002-03-28
2004-05-11
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
Bearing, seal, or liner between runner portion and static part
Between blade edge and static part
C415S174400, C415S213100, C416S191000
Reexamination Certificate
active
06733235
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to turbine engine shroud segments and shroud segment assemblies including a surface exposed to elevated temperature engine gas flow. More particularly, it relates to air cooled gas turbine engine shroud segments, for example used in the turbine section of a gas turbine engine, and made of a low ductility material.
A plurality of gas turbine engine stationary shroud segments assembled circumferentially about an axial flow engine axis and radially outwardly about rotating blading members, for example about turbine blades, defines a part of the radial outer flowpath boundary over the blades. As has been described in various forms in the gas turbine engine art, it is desirable to maintain the operating clearance between the tips of the rotating blades and the cooperating, juxtaposed surface of the stationary shroud segments as close as possible to enhance engine operating efficiency. Typical examples of U.S. patents relating to turbine engine shrouds and such shroud clearance include U.S. Pat. No. 5,071,313—Nichols; U.S. Pat. No. 5,074,748—Hagle; U.S. Pat. No. 5,127,793—Walker et al.; and U.S. Pat. No. 5,562,408—Proctor et al.
In its function as a flowpath component, the shroud segment and assembly must be capable of meeting the design life requirements selected for use in a designed engine operating temperature and pressure environment. To enable current materials to operate effectively as a shroud in the strenuous temperature and pressure conditions as exist in the turbine section flowpath of modern gas turbine engines, it has been a practice to provide cooling air to a radially outer portion of the shroud. Examples of typical cooling arrangements are described in some of the above identified patents.
The radially inner or flow path surfaces of shroud segments in a gas turbine engine shroud assembly about radially inward rotating blades are arced circumferentially to define a flowpath annular surface about the rotating tips of the blades. Such annular surface is the sealing surface for the turbine blade tips. Since the shroud is a primary element in a turbine blade clearance control system, minimizing shroud deflection and maintaining shroud radially inner surface arc or “roundness” during operation of a gas turbine engine assists in minimizing performance penalty to an engine cycle. Several operating conditions tend to distort such roundness.
One condition is the application of cooling air to the radially outer portion of a shroud segment, creating in the shroud segment a thermal gradient or differential between the radially inner shroud surface exposed to a relatively high operating gas flow temperature and the cooled radially outer surface. One result of such thermal gradient is a form of shroud segment deformation or deflection generally referred to as “chording”. At least the radially inner or flowpath surface of a shroud and its segments are arced circumferentially to define a flowpath annular surface about the rotating tips of the blades. The thermal gradient between the inner and outer faces of the shroud, resulting from cooling air impingement on the outer surface, causes the arc of the shroud segments to chord or tend to straighten out circumferentially. As a result of chording, the circumferential end portions of the inner surface of the shroud segment tend to move radially outwardly in respect to the middle portion of the segment.
In addition to thermal distorting forces generated by such thermal gradient are distorting fluid pressure forces, acting on the shroud segment. Such forces result from a fluid pressure differential between the higher pressure cooling air on the shroud segment radial outer surface and the axially decreasing lower pressure engine flowstream on the shroud radially inner surface. With the cooling air maintained at a substantially constant pressure on the shroud radially outer surface during engine operation, such fluid pressure differential on a shroud segment increases axially downstream through the engine in a turbine section as the turbine extracts power from the gas stream. This action reduces the flow stream pressure progressively downstream. Such pressure differential tends to force the axial end portions, more so the axially aft or downstream portion, of a shroud segment radially inwardly. Therefore, a complex array of forces and pressures act to distort and apply pressures to a turbine engine shroud segment during engine operation to change the roundness of the arced shroud segment assembly radially inner surface. It is desirable in the design of such a turbine engine shroud and shroud assembly to compensate for such forces and pressures acting to deflect or distort the shroud segment.
Metallic type materials currently and typically used as shrouds and shroud segments have mechanical properties including strength and ductility sufficiently high to enable the shrouds to be restrained against such deflection or distortion resulting from thermal gradients and pressure differential forces. Examples of such restraint include the well known side rail type of structure, or the C-clip type of sealing structure, for example described in the above identified Walker et al patent. That kind of restraint and sealing results in application of a compressive force at least to one end of the shroud to inhibit chording or other distortion.
Current gas turbine engine development has suggested, for use in higher temperature applications such as shroud segments and other components, certain materials having a higher temperature capability than the metallic type materials currently in use. However such materials, forms of which are referred to commercially as a ceramic matrix composite (CMC), have mechanical properties that must be considered during design and application of an article such as a shroud segment. For example, as discussed below, CMC type materials have relatively low tensile ductility or low strain to failure when compared with metallic materials. Also, CMC type materials have a coefficient of thermal expansion (CTE) in the range of about 1.5-5 microinch/inch/° F., significantly different from commercial metal alloys used as restraining supports or hangers for metallic shrouds and desired to be used with CMC materials. Such metal alloys typically have a CTE in the range of about 7-10 microinch/inch/° F. Therefore, if a CMC type cooled on one surface during operation, forces can be developed in CMC type segment sufficient to cause failure of the segment.
Generally, commercially available CMC materials include a ceramic type fiber for example SiC, forms of which are coated with a compliant material such as BN. The fibers are carried in a ceramic type matrix, one form of which is SiC. Typically, CMC type materials have a room temperature tensile ductility of no greater than about 1%, herein used to define and mean a low tensile ductility material. Generally CMC type materials have a room temperature tensile ductility in the range of about 0.4-0.7%. This is compared with metallic shroud and/or supporting structure or hanger materials having a room temperature tensile ductility of at least about 5%, for example in the range of about 5-15%. Shroud segments made from CMC type materials, although having certain higher temperature capabilities than those of a metallic type material, cannot tolerate the above described and currently used type of compressive force or similar restraint force against chording and other deflection or distortion. Neither can they withstand a stress rising type of feature, for example one provided at a relatively small bent or filleted surface area, without sustaining damage or fracture typically experienced by ceramic type materials. Furthermore, manufacture of articles from CMC materials limits the bending of the SiC fibers about such a relatively tight fillet to avoid fracture of the relatively brittle ceramic type fibers in the ceramic matrix. Provision of a shroud segment of such a low ductility material, particularly in combination or assembly with a shroud s
Alford Mary Ellen
Darkins, Jr. Toby George
Fessler Madeleine Elise
Noe Mark Eugene
General Electric Company
Kershteyn Igor
Look Edward K.
Narciso David L.
Sachs Lee H.
LandOfFree
Shroud segment and assembly for a turbine engine does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Shroud segment and assembly for a turbine engine, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Shroud segment and assembly for a turbine engine will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3206259