Turbine engine shroud segment

Abstract

A turbine engine shroud segment comprises a body including an outer surface away from which an integral attachment system projects. The attachment system comprises a plurality of at least two axially spaced apart circumferentially extending rows of discrete projection hook segments to interrupt a potential hoop stress path through the attachment system. Each projection hook segment includes a segment support surface aligned circumferentially and radially with other segment support surfaces in a row.

Description

[0001] The Government has rights in this invention pursuant to Contract No. F33615-97-C-2778-7UW awarded by the Department of Air Force.BACKGROUND OF THE INVENTION [0002] This invention relates generally to turbine engine shroud segments 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. [0003] A turbine engine shroud segment is a stationary engine component separate and distinct from a component that includes an airfoil, for example a nozzle segment or a stationary blading member. In a gas turbine engine, a plurality of stationary shroud segments is assembled circumferentially about an axial flow engine axis and radially about and spaced apart from rotating blading members, for example about rotating turbine blades. Together, such shroud segments define a part of the radial flowpath b...

AI Technical Summary

Benefits of technology

[0013] According to embodiments of the present invention, to interrupt or cut a potential hoop stress path through the attachment system of integral projection hooks and to reduce hoop stress induced by a radial temperature gradient in the projection hooks of the attachment system, there is provided a plurality of individual, discrete projection hook segments. Such projection hook segments are in at least two axially spaced-apart circumferentially extending rows defining the attachment system. Each row comprises a plurality of the discrete projection hook segments spaced-apart circumferentially along the body outer surface at least partially between the first and second circumferential edge portions. Each hook end portion of each projection hook segment in a row faces an axial edge portion, and each segment support surface of each projection hook is aligned circumferentially and radially with other segment support surfaces in a row.

Problems solved by technology

However as is well known in the art, for example as described in some of the above identified patents, provision of such cooling air is at the expense of engine efficiency.

However, cooling air leakage about edges of a shroud segment can reduce designed efficiency by wasting cooling airflow.

It has been observed that one source of such segment edge leakage can result from shroud segment deformation such as deflection or distortion, generally referred to as “chording”.

As is well known in the gas turbine engine art, other segment distortion or distortion forces can occur, for example in a high pressure turbine.

Other known shroud segment restraints or attachment systems can result in significant hoop stress development in an integral attachment system.

Such metal alloys typically have a CTE in the range of about 7-10 microinch / inch / ° F. Therefore, if a CMC type of shroud segment is restrained and cooled on one surface during operation, forces or stresses can be developed in CMC type segment sufficient to cause failure of the segment or its integral attachment system.

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.

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.

In some applications and embodiments using CMC materials as a shroud segment, high pressure loading on a shroud segment integral attachment system, coupled with radial temperature gradients, can develop hoop stress amounts in a substantially continuous path through such attachment system that can result in failure of the attachment system.

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