Apparatus and methods for cooling turbine bucket platforms

Abstract

A turbine bucket includes a platform interfacing between an airfoil and a shank. The platform is provided with a plurality of cavities covered by impingement cooling plates along the platform underside. Purge air supplied in the gaps between adjacent buckets flows through holes in the impingement plates to impingement cool opposite wall portions of the platform. The cooling air in the cavities is transmitted through film cooling holes in the platform to form a thin film of insulating air along the surface of the platform exposed to the hot gas in the hot gas path.

Description

BACKGROUND AND BRIEF DESCRIPTION OF THE INVENTION [0001] The present invention relates to cooling turbine bucket platforms at the interface between the turbine airfoils and the shanks of the buckets, and particularly relates to apparatus and methods for flowing a cooling medium for impingement and convective cooling of the bucket platform. [0002] Over the years, gas turbines have trended towards increased inlet firing temperatures to improve output and engine efficiencies. As gas path temperatures have increased, bucket platforms have increasingly exhibited distress including oxidation, creep and low cycle fatigue cracking. In certain turbines, temperature inlet profiles have become such that the platforms are seeing close to the peak inlet temperatures for the blade row. This exacerbates the potential distress on bucket platforms as these blades run even hotter. [0003] Many prior bucket designs did not require active cooling of the platform due to low firing temperatures. Also, fil...

AI Technical Summary

Benefits of technology

[0002] Over the years, gas turbines have trended towards increased inlet firing temperatures to improve output and engine efficiencies. As gas path temperatures have increased, bucket platforms have increasingly exhibited distress including oxidation, creep and low cycle fatigue cracking. In certain turbines, temperature inlet profiles have become such that the platforms are seeing close to the peak inlet temperatures for the blade row. This exacerbates the potential distress on bucket platforms as these blades run even hotter.

[0003] Many prior bucket designs did not require active cooling of the platform due to low firing temperatures. Also, film cooling carryover from upstream nozzle side walls tended to lower the temperatures near the platforms from the resulting “pitch-line bias” of the inlet temperature profile. Newer bucket designs have utilized film cooling by drilling holes through the platform and using compressor discharge air to flow a layer of film air on the platform surface exposed to the hot gas path, protecting it from the high flow path temperatures. This, however, is limited to areas where there is sufficient pressure to inject the air to film cool surface portions of the platform exposed to the hot gas flow path. Many current bucket designs only have sufficient pressure to film cool the aft section of the platform where the gas flow path air has been accelerated to drop the local static pressure. Accordingly, there is the need to reduce the platform temperature to a level required to meet part life or durability requirements including oxidation, creep and low cycle fatigue cracking.

Problems solved by technology

As gas path temperatures have increased, bucket platforms have increasingly exhibited distress including oxidation, creep and low cycle fatigue cracking.

This exacerbates the potential distress on bucket platforms as these blades run even hotter.

Also, film cooling carryover from upstream nozzle side walls tended to lower the temperatures near the platforms from the resulting “pitch-line bias” of the inlet temperature profile.

This, however, is limited to areas where there is sufficient pressure to inject the air to film cool surface portions of the platform exposed to the hot gas flow path.

Many current bucket designs only have sufficient pressure to film cool the aft section of the platform where the gas flow path air has been accelerated to drop the local static pressure.

Images