Patent ID: 7507069

Claim:
A gas turbine, comprising a compressor for producing compressed air, a combustor for mixing and burning the compressed air and fuel, and a turbine rotated by combustion gases exiting said combustor, said turbine including a gas path formed therein between a casing and a turbine rotor for passage of the combustion gases, a nozzle vane and a diaphragm engaging with said nozzle vane which are disposed in a channel of the downward flowing combustion gases on the outlet side of said gas path, an upstream-side wheel space and a downstream-side wheel space formed between said diaphragm and corresponding rotor blades, and holes formed in upstream- and downstream-side lateral walls of said diaphragm for communication with said upstream-side wheel space and said downstream-side wheel space to supply a coolant in said diaphragm to said upstream-side wheel space and said downstream-side wheel space, wherein said turbine further includes a plurality of engagement portions between said diaphragm and said nozzle vane, which are provided successively from the upstream side toward the downstream side in a direction of flow of the combustion gases, a first nozzle vane hook and a first diaphragm hook arranged to provide a relatively upstream one of said plurality of engagement portions with a first contact interface thereof formed in a circumferential direction of a circle defined about a turbine rotary shaft, and a second nozzle vane hook and a second diaphragm hook arranged to provide a relatively downstream one of said plurality of engagement portions with a second contact interface thereof formed in a direction across the turbine rotary shaft, said engagement portion provided with the second contact interface being downstream with respect to said engagement portion provided with the first contact interface, relative to the direction of flow of the combustion gases, wherein said diaphragm and said nozzle vane are arranged to define a cavity that is sealed from said downstream-side wheel space at said second contact interface, wherein said second contact interface includes a first contact surface of said second diaphragm hook and a second contact surface of said second nozzle vane hook that faces and contacts said first contact surface to form said second contact interface, said first contact surface being positioned upstream of said second contact surface relative to the direction of flow of the combustion gases, and wherein said second nozzle vane hook has a recessed step portion defined by a flat plane shifted from the second contact interface at a downstream side and in an axial direction of said turbine rotary shaft, and said recessed step portion is formed in an upstream surface of said second nozzle vane hook adjacent said second contact surface of said second nozzle vane hook, and a boundary of said recessed step portion which is a boundary defining an edge of said second contact surface is formed substantially linearly.