Impingement plate for damping and cooling shroud assembly inter segment seals

An impingement plate is cooperable with a shroud assembly. The shroud assembly includes an outer shroud and plural inner shrouds with seals between the plural inner shrouds, respectively. The impingement plate includes a trailing edge portion, a leading edge portion and a mid portion between the trailing edge portion and the leading edge portion. A plurality of impingement holes are formed across an area of the impingement plate, and a cooling and damping section includes at least one channel that is shaped to accelerate cooling flow through the impingement plate.

BACKGROUND OF THE INVENTION

The invention relates generally to an impingement plate in a turbine shroud assembly.

In industrial gas turbines, shroud segments are fixed to turbine shell hooks in an annular array about the turbine rotor axis to form an annular shroud radially outwardly of and adjacent the tips of buckets forming part of the turbine rotor. The inner wall of the shroud defines part of the gas path. Conventionally, the shroud segments are comprised of inner and outer shrouds provided with complimentary hooks and grooves adjacent to their leading (forward) and trailing (aft) edges for joining the inner and outer shrouds to one another. The outer shroud is, in turn, secured to the turbine shell or casing. Typically, each shroud segment has one outer shroud and two or three inner shrouds.

The shrouds prevent the turbine shell from being exposed to the hot gas path. The shrouds, especially in the first and second stages, are exposed to very high temperatures of the hot gas in the hot gas path and have heat transfer coefficients that are also very high due to the rotation of the turbine blades. Inner shrouds are made from high temperature resistant material and are exposed to the hot gas path. The inner shrouds may also have thermal boundary coatings. The outer shrouds are made from lower temperature resistant and lower cost materials compared to the inner shrouds. To cool the inner and outer shrouds, cold air from the compressor is used.

Different cooling and sealing methods are used. The most common method is impingement cooling to cool the radially outer side of the inner shroud. An impingement plate may be interposed between the inner and outer shrouds to distribute the cooling air.

Each outer shroud in the shroud assembly may include multiple inner shrouds with inter segment seals between them. The inter segment seals, however, are subject to HCF failures due to bucket pulsations. Additionally, the seals have a tendency to fail in the mid to leading edge span of the seal due to high oxidation damage. The damage results from hot gas ingestion that thereby raises the temperature of the seals. Existing designs have no dedicated cooling for the inter segment seals between the inner shrouds in a shroud assembly.

BRIEF DESCRIPTION OF THE INVENTION

In an exemplary embodiment, an impingement plate is cooperable with a shroud assembly. The shroud assembly includes an outer shroud and plural inner shrouds with seals between the plural inner shrouds, respectively. The impingement plate includes a trailing edge portion, a leading edge portion and a mid portion between the trailing edge portion and the leading edge portion. A plurality of impingement holes are formed across an area of the impingement plate, and a cooling and damping section includes at least one channel that is shaped to accelerate cooling flow through the impingement plate.

In another exemplary embodiment, a shroud assembly includes an outer shroud including outer shroud hooks at an inner end thereof, plural inner shrouds including connecting structure securable to the outer shroud hooks, and a seal connected between adjacent ones of the plural inner shrouds. An impingement plate with a cooling and damping section is disposed between the outer shroud and the plural inner shrouds.

In still another exemplary embodiment, a method of cooling and dampening seals between inner shrouds in a shroud assembly includes the steps of (a) interposing an impingement plate between an outer shroud and the inner shrouds; (b) directing cooling air through the impingement plate; and (c) accelerating the cooling air through the impingement plate adjacent the seals.

DETAILED DESCRIPTION OF THE INVENTION

Although the invention will be described with reference to an industrial gas turbine, the invention is applicable in other environments as would be appreciated by those of ordinary skill in the art. The invention is thus not meant to be limited to gas turbines.

With reference toFIGS. 1 and 2, in an industrial gas turbine, shroud segments or shroud assemblies12are fixed to turbine shell hooks in an annular array about the turbine rotor axis to form an annular shroud radially outwardly of and adjacent the tips of buckets14forming part of the turbine rotor. Conventionally, the shroud segments are comprised of inner16and outer18shrouds provided with complimentary hooks17and grooves19adjacent their leading (forward) and trailing (aft) edges for joining the inner and outer shrouds to one another. The outer shroud18is secured to the turbine shell or casing. In use, to cool the inner and outer shrouds, cold air from the compressor is used. Impingement cooling may be used to cool the radially outer side of the inner shroud16. An impingement plate20may be welded to the outer shroud18and interposed between the inner and outer shrouds to distribute the cooling air.

With reference toFIG. 3, in the existing shroud assembly, discharge air flows through the impingement plate20via holes22. In one arrangement, the discharge air comes through a hole provided in a hula seal to cool the combustion liner by the impingement plate20. In this process, the hula seal is also cooled by the same discharge air kept in the plenum. In the existing configuration, however, inter segment seals24between the inner shrouds may be subjected to HCF failures due to inadequate cooling and pulsations from the turbine bucket.

As shown schematically inFIG. 4, the impingement plate20according to the described embodiments is provided with a cooling and damping section26in the form of a nozzle or the like adjacent the inter segment seals24between the inner shrouds16. The cooling and damping section26provides secondary flows that will impinge on the seal24directly with increased velocity. The high velocity air flow provides damping from the cooling side of the seal24that withstands and dampens the bucket pulsations to avoid HCF issues. That is, increasing the amount of cooling air on the seals will increase the pressure acting on the seals and results in improved back flow margins and hence dampens the bucket pulsations. Additionally, the cooling and damping section26provides for direct cooling of the seal24, which will avoid oxidation problems that currently exist. An advantageous consequence of the cooling and damping section26is the resulting additional stiffness to the impingement plate20, which can eliminate any lifting issues on the impingement plate20.

FIGS. 5 and 6show an exemplary configuration of the impingement plate20including the cooling and damping section26. As shown, the impingement plate20includes a trailing edge portion28, a leading edge portion30, and a mid portion32between the trailing edge portion28and the leading edge portion30. The impingement holes22are formed across an area of the impingement plate20. The cooling and damping section26includes at least one channel that is shaped to accelerate cooling flow through the impingement plate20.

FIG. 5shows an underside of the impingement plate20, andFIG. 6is a sectional view through A-A inFIG. 5. Preferably, the cooling and damping section26extends from the leading edge portion30to the mid portion32.

In order to accelerate the cooling flow through the impingement plate20, the at least one channel comprises a converging diameter in a flow direction. In the embodiment shown inFIGS. 5 and 6, the cooling and damping section26includes a series of conical channels34-37. The conical channels34-37are sized according to an amount of damping desired at the plural inner shrouds16adjacent the impingement plate20. As such, the amount of cooling/damping can be “tuned” based on the turbine design. In the exemplary embodiment shown inFIGS. 5 and 6, conical channels34and37are larger than conical channels35and36.

FIG. 7shows an alternative embodiment for the impingement plate20. InFIG. 7, the cooling and damping section26comprises a trapezoidal shaped channel40. As shown, the trapezoidal shaped channel40extends from the leading edge portion30to the mid portion32.

The improved impingement plate and shroud assembly serves to dampen turbine bucket pulsations, thereby reducing vibrations at the inter segment seals between inner shrouds and consequently reducing or eliminating failures due to HCF. Additionally, the dedicated cooling for the seals reduces high oxidation damage caused by hot gas ingestion during turbine use. The structure also minimizes impingement plate cracks, thereby reducing repair costs. Still further, the arrangement increases seal life and consequently the useful life of the inner shrouds, thereby significantly reducing repair cycles and outage issues.