COOLING PASSAGE CONFIGURATION FOR TURBINE ENGINE AIRFOILS

TECHNICAL FIELD

The present invention relates to turbine engines, and, more particularly, to cooling passages provided in a wall of a turbine engine airfoil.

BACKGROUND ART

In a turbomachine, such as a gas turbine engine, air is pressurized in a compressor then mixed with fuel and burned in a combustor to generate hot combustion gases. The hot combustion gases are expanded within a turbine of the engine where energy is extracted to power the compressor and to provide output power used to produce electricity. The hot combustion gases travel through a series of stages when passing through the turbine. A stage may include a row of stationary airfoils, i.e., vanes, followed by a row of rotating airfoils, i.e., blades, where the blades rotate to extract energy from the hot combustion gases for powering the compressor and providing output power.

Since the airfoils, i.e., vanes and blades, are directly exposed to the hot combustion gases as the gases pass through the turbine, the airfoils are typically provided with internal cooling circuits that channel a cooling fluid, such as compressor discharge air, through the airfoil and through various film cooling holes around the surface thereof. For example, film cooling holes are typically provided in the walls of the airfoils for channeling the cooling air through the walls for discharging the air to the outside of the airfoil to form a layer of film cooling air, which protects the airfoil from the hot combustion gases.

Film cooling effectiveness is related at least in part to the concentration of the film cooling air at the surface being cooled. In general, the greater the cooling effectiveness, the more efficiently the surface is cooled. A decrease in cooling effectiveness increases the amount of cooling air necessary to maintain a certain cooling capacity, which may cause a decrease in engine efficiency. SUMMARY OF INVENTION

In accordance with a first aspect of the present invention, an airfoil is provided in a turbine engine. The airfoil comprises a substrate and at least one cooling passage. The substrate includes an inner surface and an outer surface opposed from the inner surface, wherein a thickness is defined between the inner and outer surfaces. The substrate extends in a spanwise direction from an inner end of the airfoil to a tip of the airfoil opposed from the inner end. The least one cooling passage delivers cooling fluid from a cooling fluid source located within the airfoil to the outer surface of the substrate. The at least one cooling passage extends through the substrate at an angle and includes an inlet at the inner surface of the substrate and an outlet at the outer surface of the substrate, the inlet spaced from the outlet in an axial direction extending parallel to the outer surface of the substrate. Each cooling passage includes an entrance portion extending from the inlet and receiving cooling fluid from the cooling fluid source, and a diffusion portion axially downstream from the entrance portion and receiving cooling fluid from the entrance portion. The diffusion portion includes: a floor wall defining an inner boundary of the diffusion portion and meeting the outer surface of the substrate at a floor junction; a ceiling wall opposed from the floor wall and defining an outer boundary of the diffusion portion, the ceiling wall meeting the outer surface of the substrate at a ceiling junction axially upstream from the floor junction; opposed first and second sidewalls defining lateral boundaries of the diffusion portion and meeting the outer surface of the substrate at respective first and second sidewall junctions; and the outlet at the outer surface of the substrate, wherein the outlet is defined by the floor junction, the ceiling junction, the first sidewall junction, and the second sidewall junction. Within each cooling passage: the floor wall diverges from the ceiling wall at a floor diverging location, the floor diverging location substantially axially in plane with the ceiling junction; the first sidewall diverges from the second sidewall at a first sidewall diverging location; the second sidewall diverges from the first sidewall at a second sidewall diverging location; and the second sidewall diverges from the first sidewall a second time at a third sidewall diverging location, the third sidewall diverging location axially downstream from the second sidewall diverging location.

The entrance portion of the at least one cooling passage may define a metering portion of the cooling passage and may have a generally constant cross- sectional shape. The entrance portion of the at least one cooling passage my have a cross section having one of a circular, ovular, and rectangular shape.

The floor diverging location of the at least one cooling passage may be a second floor diverging location, and the floor wall of the at least one cooling passage may diverge from the ceiling wall at a first floor diverging location, the first floor diverging location upstream from the second floor diverging location. The ceiling wall of the at least one cooling passage may diverge from the floor wall at a ceiling diverging location. The ceiling diverging location may be substantially axially in plane with first floor diverging location.

The first and second sidewall diverging locations of the at least one cooling passage may be substantially axially in plane with one another.

The angle at which the at least one cooling passage extends through the substrate may coincide with a direction of hot gas flow over the outer surface of the substrate such that cooling fluid discharged from the outlet of the at least one cooling passage includes a velocity component in the same direction as the direction of hot gas flow.

The inlet and the outlet of the at least one cooling passage may both have an ovular or circular cross-sectional shape and the outlet may have a larger cross- sectional area than the inlet.

In accordance with a second aspect of the present invention, an airfoil is provided in a turbine engine. The airfoil comprises a substrate and at least one cooling passage. The substrate includes an inner surface and an outer surface opposed from the inner surface, wherein a thickness is defined between the inner and outer surfaces. The substrate extends in a spanwise direction from an inner end of the airfoil to a tip of the airfoil opposed from the inner end. The least one cooling passage delivers cooling fluid from a cooling fluid source located within the airfoil to the outer surface of the substrate. The at least one cooling passage extends through the substrate at an angle and includes an inlet at the inner surface of the substrate and an outlet at the outer surface of the substrate, the inlet spaced from the outlet in an axial direction extending parallel to the outer surface of the substrate. Each cooling passage includes an entrance portion extending from the inlet and receiving cooling fluid from the cooling fluid source, and a diffusion portion axially downstream from the entrance portion and receiving cooling fluid from the entrance portion. The diffusion portion includes: a floor wall defining an inner boundary of the diffusion portion and meeting the outer surface of the substrate at a floor junction; a ceiling wall opposed from the floor wall and defining an outer boundary of the diffusion portion, the ceiling wall meeting the outer surface of the substrate at a ceiling junction axially upstream from the floor junction; opposed first and second sidewalls defining lateral boundaries of the diffusion portion and meeting the outer surface of the substrate at respective first and second sidewall junctions; and the outlet at the outer surface of the substrate, wherein the outlet is defined by the floor junction, the ceiling junction, the first sidewall junction, and the second sidewall junction. Within each cooling passage: the floor wall diverges from the ceiling wall at a first floor diverging location; the floor wall diverges from the ceiling wall a second time at a second floor diverging location, the second floor diverging location axially downstream from the first floor diverging location; the ceiling wall diverges from the floor wall at a ceiling diverging location; the first sidewall diverges from the second sidewall at a first sidewall diverging location; the second sidewall diverges from the first sidewall at a second sidewall diverging location; and the second sidewall diverges from the first sidewall a second time at a third sidewall diverging location, the third sidewall diverging location axially downstream from the second sidewall diverging location.

The entrance portion of the at least one cooling passage may define a metering portion of the cooling passage and may have a generally constant cross- sectional shape. The entrance portion of the at least one cooling passage may have a cross section having one of a circular, ovular, and rectangular shape. The first floor diverging location of the at least one cooling passage may be substantially axially in plane with ceiling diverging location.

The second floor diverging location of the at least one cooling passage may be substantially axially in plane with the ceiling junction.

The first and second sidewall diverging locations of the at least one cooling passage may be substantially axially in plane with one another.

The angle at which the at least one cooling passage extends through the substrate may coincide with a direction of hot gas flow over the outer surface of the substrate such that cooling fluid discharged from the outlet of the at least one cooling passage includes a velocity component in the same direction as the direction of hot gas flow.

The inlet and the outlet of the at least one cooling passage may both have an ovular or circular cross-sectional shape and the outlet may have a larger cross- sectional area than the inlet.

BRIEF DESCRIPTION OF DRAWINGS

While the specification concludes with claims particularly pointing out and distinctly claiming the present invention, it is believed that the present invention will be better understood from the following description in conjunction with the accompanying Drawing Figures, in which like reference numerals identify like elements, and wherein:

Fig. 1 is a schematic side view of an airfoil including a plurality of film cooling passages according to an aspect of the present invention;

Fig. 2 is a cross-sectional view of a film cooling passage extending through a wall of the airfoil of Fig. 1 ;

Fig. 3 is a cross-sectional view taken along line 3-3 in Fig. 2;

Fig. 4 is an end view of the film cooling passage illustrated in Fig. 2, looking straight into the film cooling passage from an outer surface of the airfoil; and

Fig. 5 is an enlarged perspective view of the film cooling passage illustrated in Fig. 2 showing its orientation with respect to radial and streamwise directions of the airfoil. DESCRIPTION OF EMBODIMENTS

In the following detailed description of the preferred embodiment, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, and not by way of limitation, a specific preferred embodiment in which the invention may be practiced. It is to be understood that other

embodiments may be utilized and that changes may be made without departing from the spirit and scope of the present invention. As used throughout, the terms

"circumferential," "axial," "inner," "radial," "outer," and derivatives thereof are not intended to be limiting with regard to orientation of the elements recited for the present invention. Further, the terms "first," "second," "third," and the like used throughout the detailed description may not strictly corresponding to the use of these terms in the claims. However, the use of these terms in both the detailed description and claims is believed to provide one skilled in the art with a full understanding of the invention without an undue burden.

Referring to Fig. 1 , an airfoil 10, e.g., a rotating turbine blade as shown in Fig. 1 or a stationary turbine vane, according to aspects of the present invention is shown. The airfoil 10 includes a pressure side PS, a suction side SS, a leading edge LE, a trailing edge TE, an inner end IE affixed to a platform PL, and a tip Tl opposed from the inner end IE. A spanwise direction D _S p corresponds to a radial direction and extends between the inner end IE and the tip Tl of the airfoil 10, and a streamwise direction D _ST extends across the airfoil 10 from the leading edge LE to the trailing edge TE. It is noted that the airfoil 10 could also be a rotating

compressor blade or stationary compressor vane.

The airfoil 10 comprises a substrate 12 extending in the spanwise direction

Dsp from the inner end IE of the airfoil 10 to the tip Tl of the airfoil 10. The substrate 12 includes an inner surface 14 and an outer surface 16 opposed from the inner surface 14, wherein an axial direction A _D extends parallel to the outer surface 16, see Fig. 2. The inner surface 14 may be referred to as the "cool" surface, as the inner surface 14 defines a cooling fluid chamber 15 containing cooling fluid C _F (see Fig. 2), such as, for example, compressor discharge air, wherein the cooling fluid chamber 15 defines a cooling fluid source. The outer surface 16 may be referred to as the "hot" surface, as the outer surface 16 may be exposed to hot combustion gases H _G during operation, see Fig. 1 . Such combustion gases H _G may have temperatures of up to about 2,000° C during operation of the engine. In the embodiment shown, the inner surface 14 and the outer surface 16 are opposed and substantially parallel to each other, although this need not be the case. As used herein, the term "cooling fluid chamber" is meant to include a single chamber or a plurality of chambers defined within the substrate 12, which could be in

communication with each other or isolated from one another.

The material forming the substrate 12 may vary depending on the application of the airfoil 10. For example, the substrate 12 preferably comprises a material capable of withstanding typical operating conditions that occur within the engine, such as, for example, ceramics and metal-based materials, e.g., a steel, nickel, cobalt, or iron based superalloy, etc. As will be appreciated by those having ordinary skill in the art, the substrate 12 may comprise one or more layers, such as a base layer, a thermal barrier coating (TBC) layer, and a bond coat that functions as an adhesive for securing the TBC layer to the base layer. The base layer may be formed from, for example, a steel, nickel, cobalt, or iron based superalloy. The layers collectively provide the substrate 12 with a thickness T extending from the inner surface 14 to the outer surface 16, see Fig. 2.

The airfoil 10 includes at least one, and preferably a series of cooling passages 20 that extend through the substrate 12 from the inner surface 14 to the outer surface 16. The cooling passages 20 deliver cooling fluid C _F from the chamber 15 to the outer surface 16 of the substrate 12. If multiple cooling passages 20 are present in the airfoil 10, the cooling passages 20 may be spaced apart from each other in any suitable pattern or randomly, e.g., as dictated by cooling requirements of the substrate 12. In the exemplary embodiment shown, the cooling passages 20 are located on the pressure side PS of the airfoil 10 near the trailing edge TE. The cooling passages 20 of the present invention may also be

concentrated in other areas, such as on the suction side SS of the airfoil 10 near the leading edge LE. Assuming multiple cooling passages 20 are present in the airfoil 10, a single one of the cooling passages 20 will now be described, it being understood that the remaining cooling passages 20 may be substantially identical to the described cooling passage 20.

With reference to Figs. 2-5, the cooling passage 20 includes an entrance portion 22 that defines an opening 24 located at the inner surface 14 of the substrate 12. The entrance portion 22 may have an ovular shape as shown in Fig. 4, a rectangular shape, a circular shape or any other suitable shape. The entrance portion 22 receives cooling fluid C _F from the chamber 15 via the inlet 24 and defines a metering portion 26 for metering cooling fluid C _F passing into the cooling passage 20. As shown in Figs. 2 and 3, the entrance portion 22 may have a generally constant cross-sectional shape.

Referring to Fig. 2, the entrance portion 22 includes a central axis C _A extending through the substrate 12 at an axis angle β relative to the outer surface 16 of the substrate 12, which axis angle β may be, for example, about 20 to 60° relative to the outer surface 16 of the substrate 12. The entrance portion 22 extends through the substrate 12 at the axis angle β from the inlet 24 to a diffusion portion 28 of the cooling passage 20. As shown in Figs. 2 and 3, the metering portion 26 is positioned axially upstream from the diffusion portion 28 with regard to a flow direction of the cooling fluid C _F passing through the cooling passage 20.

The diffusion portion 28 of the cooling passage 20 extends from the entrance portion 22 to the outer surface 16 of the substrate 12 at an outlet 30 spaced from the inlet 24 in the axial direction A _D , the outlet 30 defining an open top portion of the cooling passage 20 for discharging the cooling fluid C _F from the cooling passage 20. The diffusion portion 28 includes and is defined by a floor wall 32, a ceiling wall 34 opposed from the floor wall 32, and opposed first and second diverging sidewalls 36, 38.

The floor wall 32 defines an inner boundary of the diffusion portion 28 and meets the outer surface 16 of the substrate 12 at a floor junction 40 located at an aft end portion 42 of the cooling passage 20. The floor wall 32 may be curved as shown most clearly in Fig. 4, or the floor wall 32 may define a relatively flat/planar surface.

The ceiling wall 34 defines an outer boundary of the diffusion portion 28 and meets the outer surface 16 of the substrate 12 at a ceiling junction 44 axially upstream from the floor junction 40. The ceiling wall 34 may be curved as shown most clearly in Fig. 4, or the ceiling wall 34 may define a relatively flat/planar surface.

The first and second sidewalls 36, 38 define lateral boundaries of the diffusion portion 28 and meet the outer surface 16 of the substrate 12 at respective first and second sidewall junctions 46, 48. The first and second sidewalls 36, 38 may be curved as shown most clearly in Fig. 4, or the first and second sidewalls 36, 38 may define a relatively flat/planar surface.

The floor junction 40, ceiling junction 44, and first and second sidewall junctions 46, 48 collectively define the outlet 30 of the cooling passage 20 and provide the outlet 30 in the embodiment shown with a generally ovular shape when viewed in a direction straight into the cooling passage 20, see Fig. 4. As shown most clearly in Fig. 4, the outlet 30 has a larger cross-sectional area than the inlet 24, which effects the metering of cooling fluid C _F provided by the metering portion 26. It is noted that the outlet 30 may have other shapes without departing from the spirit and scope of the invention, such as a rectangular shape, a circular shape or any other suitable shape.

As shown in Fig. 2, the floor wall 32 diverges from the ceiling wall 34 at a first floor diverging location 50 and the ceiling wall 34 diverges from the floor wall 32 at a ceiling diverging location 52, which first floor and ceiling diverging locations 50, 52 are preferably substantially axially in plane with one another. As used herein, the phrase "substantially axially in plane with" is intended to mean that the two referenced articles are axially in plane or nearly axially in plane (with reference to the axial direction A _D extending parallel to the second surface 16 of the substrate 12), e.g., within a deviation of 5% of a length L of the cooling passage 20. The floor wall 32 diverges from the ceiling wall 34 a second time at a second floor diverging location 54, which second floor diverging location 54 is preferably substantially axially in plane with the ceiling junction 44.

The floor and ceiling diverging locations 50, 54, 52 result in the floor wall 32 comprising first, second, and third floor sections 32A, 32B, 32C and the ceiling wall 34 comprising first and second ceiling sections 34A, 34B. The first floor section 32A extends through the entrance portion 22 up to the first floor diverging location 50, the second floor section 32B extends from the first floor diverging location 50 to the second floor diverging location 54, and the third floor section 32C extends from the second floor diverging location 54 to the floor junction 40 at the outlet 30 of the cooling passage 20. The first ceiling section 34A extends through the entrance portion 22 up to the ceiling diverging location 52, and the second ceiling section 34B extends from the ceiling diverging location 52 to the ceiling junction 44 at the outlet 30 of the cooling passage 20. Exemplary angles for these sections 32A-C, 34A-B relative to the central axis C _A of the entrance portion 22 are as follows: the first floor section 32A and the first ceiling section 34A both extend generally parallel to the central axis C _A ; the second floor section 32B extends at an angle a of between about 5-10° and more specifically about 7° relative to the central axis C _A ; the third floor section 32C extends at an angle Θ of between about 10-20° and more specifically about 14° relative to the central axis C _A ; the second ceiling section 34B extends at an angle π of between about 2-5° and more specifically about 3° relative to the central axis C _A . Again, these values are exemplary and the invention is not intended to be limited to the specified angles.

Referring now to Fig. 3, the first sidewall 36 diverges from the second sidewall 38 at a first sidewall diverging location 60 and the second sidewall 38 diverges from the first sidewall 36 at a second sidewall diverging location 62, which first and second sidewall diverging locations 60, 62 are preferably substantially axially in plane with one another. The second sidewall 38 diverges from the first sidewall 36 a second time at a third sidewall diverging location 64, which third sidewall diverging location 64 is located axially downstream from the first and second sidewall diverging locations 60, 62 as shown in Fig. 3. As shown in Figs. 2 and 3, the first floor and ceiling diverging locations 50, 52 are preferably substantially axially in plane with the first and second sidewall diverging locations 60, 62, and the second floor diverging location 54 and the ceiling junction 44 are preferably substantially axially in plane with the third sidewall diverging location 64.

The first, second, and third sidewall diverging locations 60, 62, 64 result in the first sidewall 36 comprising first and second sidewall sections 36A, 36B and the second sidewall 38 comprising third, fourth, and fifth sidewall sections 38A, 38B, 38C. The first sidewall section 36A extends through the entrance portion 22 up to the first sidewall diverging location 60, and the second sidewall section 36B extends from the first sidewall diverging location 60 to the first sidewall junction 46 at the outlet 30 of the cooling passage 20. The third sidewall section 38A extends through the entrance portion 22 up to the second sidewall diverging location 62, the fourth sidewall section 38B extends from the second sidewall diverging location 62 to the third sidewall diverging location 64, and the fifth sidewall section 38C extends from the third sidewall diverging location 64 to the second sidewall junction 48 at the outlet 30 of the cooling passage 20. Exemplary angles for these sections 36A-B, 38A-C relative to the central axis C _A of the entrance portion 22 are as follows: the first sidewall section 36A of the first sidewall 36 and the third sidewall section 38A of the second sidewall 38 both extend generally parallel to the central axis C _A ; the second sidewall section 36B of the first sidewall 36 extends at an angle λ of between about 2-5° and more specifically about 3° relative to the central axis C _A ; the fourth sidewall section 38B of the second sidewall 38 extends at an angle Ω of between about 5-10° and more specifically about 7° relative to the central axis C _A ; the fifth sidewall section 38C of the second sidewall 38 extends at an angle μ of between about 10-20° and more specifically about 14° relative to the central axis C _A . Again, these values are exemplary and the invention is not intended to be limited to the specified angles.

The combination of the unique arrangement of the floor, ceiling, and sidewall diverging locations 50, 54, 52, 60, 62, 64 and angles provides the cooling passages 20 with a configuration that promotes a flow of cooling fluid C _F out of the outlet 30 with a substantial amount of cooling fluid C _F passing out of a radially outer corner portion 70 (see Fig. 5) of each cooling passage 20. Further, the diffusion portion 28 provides a compound or multi-section diffusion configuration, which permits the cooling fluid C _F to diffuse multiple times after it passes out of the entrance portion 22 so that a better distribution of cooling fluid C _F out of the cooling passages 20 is accomplished.

Additionally, the cooling passages 20 may be configured so as to be angled in the radial direction, i.e., in the spanwise direction D _S p, through the substrate 12, the angle coinciding with a direction of hot gas flow H _G over the outer surface 16 of the substrate 12, see Fig. 5. As a result, cooling fluid C _F is discharged from the cooling passage outlets 30 including a velocity component in the same direction as the direction of hot gas flow H _G . Hence, hot combustion gas Hg migration into the airfoil 10 is reduced and a higher level of film cooling effectiveness is achieved, thus yielding a better cooling of the airfoil 10, which translates to a longer useful life of the airfoil 10 and greater engine efficiency. The multi-section diffusion configuration in which there is greater tapering of the second sidewall 38 than the first sidewall 36, in combination with the radial angle of the cooling passages 20 through the substrate 12, also achieves greater film cooling characteristics for the cooling fluid C _F discharged by the cooling passages 20.

While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.