Gas turbine airfoil film cooling hole

Abstract

A gas turbine airfoil (1) with a pressure sidewall and a suction sidewall (6) comprises several internal cooling passages, through which cooling air flows, and several film cooling holes (7) that extend from the internal cooling passages to the outer surface (11) of the suction sidewall (6). According to the invention the film cooling holes (7) are oriented in the radial outward direction as well as toward the trailing edge of the airfoil (1). They each comprise a diffused section with sidewalls that are diffused in the radial outward direction, in the radial inward direction as well as toward downstream direction. Cooling air flowing through the diffused film cooling hole (7) onto the outer surface (6) of the airfoil (1) forms an air curtain preventing plugging of the film cooling hole by particles entrained in the hot gas flow.

Description

FIELD OF INVENTION [0001] This invention pertains to gas turbine airfoils and in particular to a cooling construction with film cooling holes and the prevention of contamination and plugging of the film cooling holes. BACKGROUND ART [0002] The airfoils of gas turbines, turbine rotor blades and stator vanes, require extensive cooling in order to keep the metal temperature below a certain allowable level and prevent damage due to overheating from the hot gas flow. Typically, such airfoils are designed with hollow spaces and a plurality of passages and cavities within the airfoil for cooling fluid to flow through. The cooling fluid is typically air bled from the compressor having a higher pressure and lower temperature compared to the gas traveling through the turbine. The higher pressure forces the air through the cavities and passages as it transports the heat away from the airfoil walls. The cooling construction further comprises film cooling holes leading from the hollow spaces wit...

AI Technical Summary

Benefits of technology

[0006] It is an object of the invention to provide a cooling construction for the suction side of a gas turbine airfoil that prevents contamination and plugging of film cooling holes by hot particles entrained in the gas flow.

[0008] The film cooling hole according to the invention causes the cooling air flow exiting from the film cooling holes onto the surface of the suction sidewall to diffuse in the radial as well as in the downstream direction. The downstream direction is defined here as the direction along the tangent of the airfoil at the point of the exit port of the film cooling hole and in the plane perpendicular to the radial direction. The diffusion in the radial as well as in the downstream direction brings about an improved film coverage, which seals the airfoil surface from hot particles in the manner of an air curtain.

[0009] Particles in the gas stream that approach a film cooling hole will flow around or over this air curtain. Thus the film cooling hole is protected from particles accumulating in its vicinity and contamination and plugging of the film cooling hole by such particles is prevented.

[0010] In a particular embodiment of the invention the sidewalls of the film cooling holes are diffused in the radially outward direction toward the tip of the airfoil as well as in the radially inward direction toward the root of the airfoil. This further improves film coverage between neighboring film cooling hole exit ports in the radial direction.

Problems solved by technology

One problem encountered in the design of the gas turbine airfoils is caused by particles entrained in the hot gas flow.

During engine operation small particles remain entrained in the gas flow while larger and heavier particles impinge on the airfoil surface and can cause local impact damage.

This problem is encountered in particular on the suction side of the airfoil and downstream from the leading edge.

The particles hence not only cause impact damage but can also prevent the air from reaching the airfoil outer surface and cause secondary damage due to loss of film cooling and resultant overheating of the airfoil.

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