Impingement cooling of a turbine airfoil with large platform to airfoil fillet radius

Abstract

A method of impingement cooling a turbine airfoil with a large platform to airfoil fillet radius which includes coring the airfoil fillet such that the fillet wall is maintained at a minimum thickness. An impingement tube is used which follows the fillet contour as it transitions from airfoil to platform and supplies impingement air to the airfoil walls. The air subsequently flows across the airfoil internal wall and finally exits the airfoil through airfoil holes to provide film cooling to the airfoil fillet.

Description

FIELD OF THE INVENTION

This invention relates generally to airfoils, and more specifically to the impingement cooling of a large platform to airfoil fillet radius on a turbine airfoil.

BACKGROUND OF THE INVENTION

In a conventional turbine airfoil, cooling air is supplied to the airfoil through an impingement tube which has been inserted into and is located adjacent the internal wall of a hollow or cored airfoil. The air travels through the impingement tube and exits through small holes toward the airfoil wall. The air exiting the impingement tube is at a high velocity and provides impingement cooling on the airfoil wall. The air then flows along the wall of the airfoil until it exits through cooling holes in the airfoil surface, where the air finally functions to film cool the airfoil. The fillet between the airfoil and platform external surfaces is typically uncooled due to its small radius size (typically 0.045-0.150).

As the size of the airfoil fillet increases from 0.150 to upwards of an inch or greater, it becomes difficult to continue to ignore cooling of the filleted region of the airfoil. The large fillet increases the area and volume of material exposed to high temperatures such that it becomes necessary to provide a method of cooling to prevent part durability shortfalls such as oxidation and or thermal mechanical fatigue. It can therefore been seen that there is a need for an effective method of cooling large filleted airfoils which is not currently available to the field.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a system for impingement cooling of a turbine airfoil with a large platform to airfoil fillet which overcomes the problems of the prior art described above.

It is another object of the present invention to provide for a method of producing an airfoil fillet with wall thicknesses similar to that of the adjacent airfoil wall.

It is a further object of the present invention to provide an impingement tube which follows the contour of both the airfoil and airfoil fillet.

It is yet another object of the invention to provide a combination of a thin walled airfoil fillet and impingement tube design which provides for optimum impingement cooling of an airfoil with a large platform to airfoil fillet radius.

The invention is directed to impingement cooling of turbine airfoils with large fillets by initially within the casting process allowing the ceramic airfoil core to follow the exterior shape of the airfoil as it transitions from the airfoil to fillet to platform. After casting of the airfoil and removing the ceramic core to produce hollow features within the airfoil, the described process provides the airfoil and fillet with similar wall thicknesses. This concept allows the fillet wall thickness to be maintained to a minimum to allow for effective cooling. A thin sheet metal impingement tube is then positioned within the hollow airfoil and is configured to follow the airfoil to fillet to platform contour at a prescribed distance from the internal wall (typically 0.02-0.100). Utilizing the thin walled fillet and impingement tube as described, it is then possible to effectively cool the fillet area. In operation, cooling air enters the turbine airfoil through the impingement tube and impinges against the internal airfoil and fillet wall as it exits through multiple holes in the impingement tube. The air then travels across the internal surface of the fillet until it turns and exits the airfoil or fillet through multiple cooling holes. The cooling air after exiting the airfoil functions to film cool the surface of the airfoil or fillet.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of these and other objects of the invention, reference will be made to the following detailed description of the invention, which is to be read in association with the following drawings, wherein:

FIG. 1 is a side elevation in section illustrating the component parts of a jet engine;

FIG. 2 is an enlarged partial view showing a turbine vane located in the first stage of the turbine section of the engine;

FIG. 3 is a partial side sectional view of a conventional airfoil with a typical fillet and associated impingement tube.

FIG. 4 is a partial side sectional view of a conventional airfoil with a large fillet.

FIG. 5 is a sectional view of a conventional airfoil with a ceramic core.

FIG. 6 is a sectional view of a cored airfoil of the present invention.

FIG. 7 is a partial section view of the airfoil of FIG. 6 with an impingement tube in place.

DETAILED DESCRIPTION OF THE INVENTION

The incorporation of large fillets into turbine airfoils requires a special method of cooling the filleted region of the airfoil. The present invention provides impingement cooling to the airfoil fillet using a uniquely designed airfoil cooling tube. In the present invention the airfoil fillet is hollowed out by coring the airfoil fillet region in the casting process such that the fillet wall does not become too thick to cool. The present invention then incorporates an impingement tube designed to follow the airfoil to fillet to platform transition at a prescribed distance, and apply impingent air through holes in the impingement tube to the internal airfoil and fillet wall. The impinged air subsequently flows through airfoil and fillet holes to the airfoil external surface and provides film cooling to the airfoil fillet.

Referring initially to FIG. 1, there is shown the main components of a jet engine, generally referenced 10 in schematic outline. The engine includes a diffuser section 12 having a conical inlet 13 in which RAM air is initially compressed and then passed on to an axial compressor 14 by means of a fan 16 located at the entrance to the compressor. Compressed air from the last stage of the compressor is fed into a series of combustion chambers, one or which is depicted as 17, where the compressed air is mixed with fuel and is ignited. Gases from the combustors are passed on to the turbine section of the engine 18 where the hot gases are expanded. The turbine section of the engine is coupled directly to the compressor by a common shaft 19. The power developed in the turbine 18 is thus utilized to drive the compressor and other auxiliary engine components. Gases leaving the turbine 18 are further expanded in the exhaust nozzle 20 of the engine and are ejected at a velocity greater than the flight velocity to produce thrust. FIG. 2 is an enlarged view of an airfoil 23 located in the first stage of the turbine 18, which is exposed to gases from the combustion chamber that are at relatively high temperatures and pressures. Accordingly, airfoil cooling which is supplied to the airfoil from areas 24 and 25 is at a premium. FIG. 3 is a section taken through airfoil 23 further illustrating the internal construction of the airfoil.

FIG. 3 shows a section of a hollow airfoil 30, having an airfoil wall 32, small fillet 36 and platform 38. The airfoil wall 32 consists of an external wall surface 31 and an internal wall surface 33 as well as a plurality of cooling holes 34. A thin sheet metal impingement tube 40 is positioned adjacent internal wall 33 at a typical distance of 0.020 to 0.100. The impingement tube 40 also contains a plurality of cooling holes 41. In this arrangement cooling air is supplied to the hollow airfoil through the impingement tube. Air exits the impingement tube by impinging onto the internal airfoil surface 33 through holes 41 in the impingement tube. The air then flows along the internal wall of the airfoil until its exits through cooling holes 34 in the airfoil surface, where it is finally used to film cool the external airfoil surface 31. The fillet 36 remains uncooled in this typical airfoil section

As the size of the airfoil fillet increases, it becomes difficult to ignore cooling this region of the airfoil and airfoil fillet. Eventually the external fillet area exposed to hot gas temperatures and the increased material contained within the fillet require that it be cooled in order to maintain part life.

In FIG. 4, airfoil 50 shows the effect on fillet area of increasing the fillet radius by conventional means. In order to cool a big fillet it first becomes necessary to hollow out the fillet at the casting stage. In airfoil manufacture the internal cavities of the airfoil are produced using ceramic cores. In the typical airfoil shown in FIG. 5, the airfoil ceramic core 48 extends radially outward of the airfoil 30.

In order to allow proper cooling of a fillet similar to that of FIG. 4 it is necessary first to hollow the fillet region of the airfoil. It has been found that this can be accomplished by allowing the ceramic core 70 (FIG. 6) to follow the exterior shape of the airfoil as it transitions from airfoil 60 to fillet 64 to platform 66. This arrangement is shown in FIG. 6. Note that the airfoil wall 62 increases in thickness as the fillet transitions from the airfoil to the platform. This is done in order to allow the core to shift radially with casting process variation without creating a minimum wall condition in the platform or fillet.

With the airfoil and fillet hollowed, it now becomes necessary to insert an impingement tube 72 (FIG. 7) into the airfoil which follows the airfoil to fillet 62 to platform 66 contour. FIG. 7 shows the big fillet airfoil 60 with an impingement tube 72 in place.

With a hollow airfoil fillet with impingement tube inserted it now becomes possible to adequately cool big fillets. Cooling air will enter into the impingement tube 72 and impinge onto the internal airfoil and fillet wall surface 74 as it exits through holes 73 in the impingement tube 72. The air will then travel across the surface of the airfoil and fillet until it turns and exits the airfoil fillet through cooling holes 68 which acts to film cool the external surface of the fillet.

While the present invention has been particularly shown and described with reference to the preferred mode as illustrated in the drawing, it will be understood by one skilled in the art that various changes in detail may be effected therein without departing from the spirit and scope of the invention as defined by the claims.

Claims

1. A method of impingement cooling a turbine airfoil with a large platform to airfoil fillet radius which contains a plurality of cooling holes through the airfoil wall which comprises: (a) coring the airfoil fillet such that the fillet wall is maintained at a minimum thickness;(b) inserting into the airfoil an impingement tube which follows the fillet contour to platform transition;(c) applying impingent air through the impingement tube to the airfoil walls and (d) using the impinged air to subsequently flow through airfoil and fillet holes to provide film cooling to the airfoil fillet.

2. The method of claim 1 in which the fillet has been cored such that the backwall of the fillet substantially follows the exterior contour of the fillet surface.

3. A system for impingement cooling a turbine airfoil with a large platform to airfoil fillet radius which contains a plurality of cooling holes through the airfoil wall which comprises: (a) an airfoil having an airfoil fillet which exhibits a fillet wall thickness similar to the wall thickness of the airfoil wall; and(b) said airfoil having an impingement tube inserted internally therein said tube being configured to follow the fillet contour to platform transition and having holes for delivery of impingement air to said airfoil fillet.

4. (canceled)

5. A method of impingement cooling a turbine airfoil with a large platform to airfoil fillet radius which comprises: (a) providing an airfoil having an airfoil fillet having a defined contour and a minimum fillet wall thickness with said airfoil having a plurality of cooling holes through the airfoil wall;(b) inserting into said airfoil an impingement tube positioned to follow the fillet contour;(c) applying impingent air through said tube to the airfoil and fillet walls;(d) with said impinged air thereby providing film cooling to the airfoil fillet.

6. A turbine airfoil which includes: (a) an airfoil fillet having a fillet wall maintained at a thickness similar to that of the airfoil side walls, with said airfoil containing a plurality of cooling holes through the airfoil wall;(b) an impingement tube inserted into said airfoil and positioned adjacent said fillet which follows the fillet contour;(c) whereby impingent air is passed through said tube to the airfoil and fillet walls to provide film cooling to the airfoil fillet.

7. The airfoil of claim 6 in which the airfoil fillet backwall is contoured to follow the contour of the exterior fillet surface.