Fluid reaction surfaces (i.e. – impellers) – With heating – cooling or thermal insulation means – Changing state mass within or fluid flow through working...
Reexamination Certificate
1998-11-06
2001-01-23
Look, Edward K. (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
With heating, cooling or thermal insulation means
Changing state mass within or fluid flow through working...
C416S09600A
Reexamination Certificate
active
06176678
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to turbine engines and, more particularly, to methods and apparatus for cooling turbine engine blades and blade platforms.
High pressure turbine blades include an airfoil that is prone to trailing edge root cracks. Propagation of these cracks leads to eventual liberation of the airfoil. The cracks can potentially progress to a complete corn-cobbed rotor. The cracks are caused, at least in part, by blade components experiencing gas temperatures beyond the material capabilities.
To satisfy blade life requirements, the airfoils typically are cooled during operation. Airfoil cooling typically is achieved by convection cooling, e.g., in serpentine passages and film openings, and by film cooling which provides a protective layer of relatively cool air over an external surface of the airfoil. Cooling requirements are typically set by high temperature component life requirements for creep rupture and oxidation at the turbine blade operating conditions.
Cracking may be aggravated by skewed dovetails and sharp pressure side bleed slot geometric configurations for the blades. These configurations may cause very early trailing edge root crack indications in factory test engines.
For example, in the art of turbine blade cooling, it is well known to align the openings in the airfoil and the platform with airfoil regions experiencing high flow path gas temperatures. Generally, thermal gradients within a given radial span, i.e., low thermal gradient between blade bulk and its edges, are reduced. Additionally, cooling levels are matched with the mechanical stresses experienced in the rotating environment.
Accordingly, it would be desirable to provide a cooling configuration that improves cooling near the root trailing edge. It would be further desirable to reduce thermal stresses in a given radial span, in particular at the trailing edge region. It would be still further desirable if the reduced thermal stresses in the trailing edge vicinity prolonged low cycle fatigue life of the blades.
BRIEF SUMMARY OF THE INVENTION
These and other objects may be attained by a turbine blade for a turbine engine that includes a plurality of trailing edge slots separated by land areas larger than the slots. More particularly, the turbine blade includes an airfoil having a suction side, a pressure side, a base, and a trailing edge connecting the suction side and the pressure side. The blade further includes a platform having a first end, a second end, a first side, and a second side. The airfoil is connected to the platform at the base of the airfoil by a fillet. The blade also includes a blade shank that is connected to the platform.
Trailing edge slots in the pressure side of the airfoil extend approximately to the trailing edge. The land areas extend a length about equal to the slot length. The slots are diffuser slots that have an exit diffusion half angle from about zero degree to about four degrees. A plurality of openings are also formed in the airfoil and are in communication with a first end of the slots. Cooling air flows out of the openings, through the slots, and over the trailing edge of the airfoil. A second end of the slots is positioned at the trailing edge of the airfoil.
The land areas include a first portion adjacent the first end of the slots and a second portion adjacent the second end of the slots. The first portion of the land area is larger than the first end of the slots and the second portion of the land area is larger than the second end of the slots.
The platform includes a plurality of openings that extend through the platform at an angle relative to a surface of the platform. The openings are positioned between the blade suction side and the platform second end and are configured to transport disk post cooling air to a surface of the platform and provide convection cooling and film cooling for the platform.
The turbine blade with the diffuser slots having a small diffusion half angle improves the match in thermal displacements from the chordwise thermal gradient along the blade trailing edge. The net stresses are thus reduced in the bottom trailing edge vicinity for a prolonged low cycle fatigue life. In addition, the platform openings further reduce the thermal stresses at the bottom trailing edge region.
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Brainch Gulcharan S.
Danowski Michael J.
General Electric Company
Hess Andrew C.
Look Edward K.
Nguyen Ninh
Young Rodney M.
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