Turbine engine component with diffuser holes

A turbine component includes a component wall with inner and outer surfaces wherein a diffuser hole passes through the component wall between the inner surface and the outer surface. The diffuser hole has a hole axis and includes: a metering section extending from an inlet at the inner surface to a junction plane between the inner and outer surfaces; and a diffuser section extending from the junction plane to an outlet at the outer surface, and increasing in flow area from the junction plane to the outlet, the diffuser section having an upstream portion defining a first area ratio and a downstream portion defining a second area ratio different from the first area ratio.

BACKGROUND OF THE INVENTION

This invention relates generally to gas turbine engines and more particularly to cooling hole structures in components of such engines.

In a gas turbine engine, air is compressed in a compressor, mixed with fuel and ignited in a combustor for generating hot combustion gases which flow downstream through one or more stages of turbine nozzles and blades. The nozzles include stationary vanes followed in turn by a corresponding row of turbine rotor blades attached to the perimeter of a rotating disk. The vanes and blades have correspondingly configured airfoils which are hollow and include various cooling circuits and features which receive a portion of air bled from the compressor for providing cooling against the heat from the combustion gases.

The turbine vane and blade cooling art discloses various configurations for enhancing cooling and reducing the required amount of cooling air in order to increase the overall efficiency of the engine while obtaining a suitable useful life for the vanes and blades. For example, typical vane and blade airfoils in the high pressure turbine section of the engine include cooling holes that extend through the pressure side, or suction side, or both, for discharging a film of cooling air along the outer surface of the airfoil to effect film cooling in a conventional manner.

A typical film cooling hole is in the form of a cylindrical aperture inclined axially through one of the airfoil sides, such as the pressure side, for discharging the film air in the aft direction. The cooling holes are typically provided in a radial or spanwise row of holes at a specific pitch spacing. In this way, the cooling holes discharge a cooling film that forms an air blanket for protecting the outer surface, otherwise known as “lands” of the airfoil from hot combustion gases during operation.

In order to improve the performance of cooling holes, it is also known to modify their shape to effect cooling flow diffusion. The diffusion reduces the discharge velocity and increases the static pressure of the airflow. Diffusion cooling holes are known in various configurations for improving film cooling effectiveness with suitable blowing ratios and backflow margin. A typical diffusion film cooling hole may be conical from inlet to outlet with a suitable increasing area ratio for effecting diffusion without undesirable flow separation. Diffusion occurs in three axes, i.e. along the length of the hole and in two in-plane perpendicular orthogonal axes. Other types of diffusion cooling holes are also found in the prior art including various rectangular-shaped holes, and holes having one or more squared sides in order to provide varying performance characteristics. Like conical diffusion holes, the rectangular diffusion holes also effect diffusion in three dimensions as the cooling air flows therethrough and is discharged along the outer surface of the airfoil.

However, prior art diffusion holes often behave like over-expanded nozzles, experiencing choking and flow shocks at operating pressure ratios. This can make their flow behavior unpredictable and reduce film cooling efficiency

Accordingly, there remains a need to further improve film cooling by providing cooling holes that promote attached film flow diffusion and downstream spreading.

BRIEF DESCRIPTION OF THE INVENTION

This need is addressed by the present invention, which provides shaped-contoured diffuser film holes having multiple diffusion angles, relatively large footprint coverage, and optional internal plug or pedestal features effective to improve attached film flow diffusion and downstream spreading.

According to one aspect of the invention, a turbine component has a component wall with inner and outer surfaces wherein a diffuser hole posses through the component wall between the inner surface and the outer surface. The diffuser hole has a hole axis and includes: a metering section extending from an inlet at the inner surface to a junction plane between the inner and outer surfaces; and a diffuser section extending from the junction plane to an outlet at the outer surface, and increasing in flow area from the junction plane to the outlet, the diffuser section having an upstream portion defining a first area ratio and a downstream portion defining a second area ratio different from the first area ratio.

According to another aspect of the invention, a turbine component has a component wall with inner and outer surfaces wherein a diffuser hole passes through the component wall between the inner surface and the outer surface. The diffuser hole has a hole axis and includes: a metering section extending from an inlet at the inner surface to a junction plane between the inner and outer surfaces; and a diffuser section extending from the junction plane to an outlet at the outer surface, and increasing in flow area from the junction plane to the outlet, the diffuser section having an upstream portion defining a first area ratio and a downstream portion defining a second area ratio different from the first area ratio; wherein the diffuser section is defined by an outer wall adjacent the outer surface, an inner wall adjacent the inner surface, and a pair of spaced-apart side walls extending between the inner and outer walls; the diffuser section includes a diffuser pedestal extending radially outwardly from the inner wall, so as to effectively divide the aft portion of the diffuser section into two separate legs.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,FIG. 1illustrates an exemplary turbine rotor blade10. The turbine blade10includes a conventional dovetail12for radially retaining the blade10to the disk as it rotates during operation. A blade shank14extends radially upwardly from the dovetail12and terminates in a platform16that projects laterally outwardly from and surrounds the shank14. The platform16defines a portion of the combustion gases past the turbine blade10. A hollow airfoil18extends radially outwardly from a root20at the platform16to a tip22. The airfoil18has a concave pressure sidewall24and a convex suction sidewall26joined together at a leading edge28and at a trailing edge30.

The turbine blade10includes an internal cooling circuit32for channeling cooling fluid “F” through the airfoil18for providing cooling during operation. The cooling circuit32may take any conventional form including various channels extending through the airfoil18, such as along the leading edge28, along the trailing edge30and along a mid-chord area in the form of a suitable serpentine fluid path. In the airfoil18shown inFIG. 1, the cooling fluid “F” may be channeled from the engine compressor and through suitable apertures between the blade dovetail12and its respective axial dovetail slot in the disk in any conventional manner.

The airfoil18is shown as incorporating a plurality of leading edge cooling holes34spaced-apart in a radially-extending row along the leading edge28for discharging the cooling fluid “F” from the cooling circuit32inside the airfoil18along its outer surface to provide a cooling film of fluid onto the surface of the airfoil18. These cooling holes34incorporate an increasing-area portion which is effective to act as a diffuser, and may thus be referred to as “diffuser film cooling holes” or simply “diffuser holes.” The present invention relates to novel designs for the diffuser holes. It is noted that the principles of the present invention are applicable to any turbine engine structure that requires film cooling in operation, such as rotating blades, stationary vanes, turbine blade shrouds, combustor liners, and the like. These structures are generally referred to herein as “turbine components”.

FIGS. 2, 3, and 4illustrate a portion of a component wall100having an inner surface102and an outer surface104. The component wall100is generically representative of a wall of the airfoil18, or any other component that includes diffuser holes. A diffuser hole106is formed in the component wall100. Only one representative diffuser hole106is shown, with the understanding that such holes are typically arrayed in rows along a component. The diffuser hole106extends from an inlet108at the inner surface102of the component wall100to an outlet110at the outer surface104of the component wall100. In operation, fluid flows from the inlet108to the outlet110, and the terms “upstream” and “downstream” are used with reference to this flow. The diffuser hole106includes a metering section112at its upstream end, and a diffuser section114at its downstream end. The metering section112may be generally cylindrical (as illustrated) or could be some other cross-sectional shape. The flow area is constant over the length of the metering section112. The two sections112and114meet at a common junction plane116. A hole axis118extends coaxially to the metering section112.

The metering section112has an area (represented by diameter “D” in the case of a cylindrical shape) which is selected, in accordance with known practices, to provide a desired mass flow rate of cooling air, given specific pressure and velocity conditions upstream and downstream of the diffuser hole106.

The diffuser section114is tapered, increasing in flow area from the metering section112to the outlet110. More specifically, a flow area “A1” at the junction plane116is smaller than a flow area “A3” at the outlet110. Laterally, the diffuser section114is bounded by an inner wall120, an outer wall122, and a pair of side walls124,126. The four walls120,122,124, and126merge together into one continuous peripheral wall at the junction plane116.

The outer wall122may extend generally parallel to the metering section112. The outer wall122may also be considered to define a “hood” of the diffuser section114. The inner wall120diverges away from the hole axis118at angle called a “layback angle,” measured in a plane perpendicular to the outer surface104of the component wall100. The side walls124,126diverge away from the hole axis118at a side diffusion angle, measured in a plane parallel to the outer surface104of the component wall100.

The diffuser section114has an upstream portion128adjacent the metering section112, and a downstream portion130adjacent the outlet110. Both the upstream portion128and the downstream portion130are tapered, increasing in flow area from the metering section112to the outlet110. More specifically, the flow area “A2” at the intersection of the upstream and downstream portions128,130is larger than a flow area “A1” at the junction plane116, and the flow area “A3” at the outlet110is larger than then flow area “A2”.

The ratio A2/A1of the upstream portion128defines a first area ratio. The ratio A3/A2of the downstream portion130defines a second area ratio. The first area ratio is selected explicitly to control flow expansion and minimize flow separation. The second area ratio is selected explicitly to effected a desired “covered area”, or area of the outer surface104that is covered by the discharged air film. The size of the covered area is determined by the lateral spread of the air film in a lateral direction (that is, a direction in the plane of the outer surface104and perpendicular to the hole axis118).

The diffuser section114thus includes two different area ratios. The boundaries of each portion128,130, may be formed by walls which are planar, curved (e.g. concave or convex), or some combination thereof. In the illustrated example the upstream portion128has a first layback angle LB1and a first side diffusion angle SD1, and the downstream portion130has a second layback angle LB2different from the first layback angle LB1, and a second side diffusion angle SD2different from the first side diffusion angle SD1. The transition between the two portions128,130may be continuous or discrete.

FIGS. 5-7illustrate a portion of a component wall200having an alternative diffuser hole206formed therein. The diffuser hole206is similar in construction to the diffuser hole106described above. Elements of the diffuser hole206which are not separately described may be considered to be identical to corresponding elements of the diffuser hole106. The diffuser hole206extends from an inlet208at the inner surface202of the component wall200to an outlet210at the outer surface204of the component wall200. The diffuser hole206includes a metering section212at its upstream end (cylindrical in this example), and a diffuser section214at its downstream end. The two sections212and214meet at a common junction plane216. A hole axis218extends coaxially to the metering section212.

The metering section212has an area (represented by diameter “D” in the case of a cylindrical shape) which is selected, in accordance with known practices, to provide a desired mass flow rate of cooling air, given specific pressure and velocity conditions upstream and downstream of the diffuser hole206.

The diffuser section214includes upstream and downstream portions228and230having different area ratios, as described above. Laterally, the diffuser section214is bounded by an inner wall220, an outer wall222, and a pair of side walls224,226. The four walls220,222,224, and226merge together into one continuous peripheral wall at the junction plane216.

The diffuser section214includes a pair of laterally-symmetrical wings232which are effectively extensions of the outer wall222. Each wing232interconnects the outer wall222and one of the side walls224,226. Each wing232has an aft edge234extending at an acute angle to the hole axis218. Collectively, the aft edges234of the two wings232form a “V”-shape with a concave curve236at its apex.FIG. 7shows only the exterior visible portions of the diffuser hole206, with the extent of the wings232(relative to the hooded area of a prior art diffuser hole) shown by dashed lines.

The wings232increase the effective hooded length of the diffuser hole206, defined as the length from the junction plane216to the aft end of the outer wall222, measured parallel to the hole axis218. The shape and dimensions of the wings232can be varied to suit a particular application.

FIGS. 8-10illustrate a component wall300having another alternative diffuser hole306formed therein. The diffuser hole306is similar in construction to the diffuser hole106described above. Elements of the diffuser hole306which are not separately described may be considered to be identical to corresponding elements of the diffuser hole106. The diffuser hole306extends from an inlet308at the inner surface302of the component wall300to an outlet310at the outer surface304of the component wall300. The diffuser hole306includes a metering section312at its upstream end (cylindrical in this example), and a diffuser section314at its downstream end. The two sections312and314meet at a common junction plane316. A hole axis318extends coaxially to the cylindrical metering section312.

The metering section312has an area (represented by diameter “D” in the case of a cylindrical shape) which is selected, in accordance with known practices, to provide a desired mass flow rate of cooling air, given specific pressure and velocity conditions upstream and downstream of the diffuser hole306.

The diffuser section314includes upstream and downstream portions328and330having different area ratios, as described above. Laterally, the diffuser section314is bounded by an inner wall320, an outer wall322, and a pair of side walls324,326. The four walls320,322,324, and326merge together into one continuous peripheral wall at the junction plane316.

The diffuser section314may include a pair of laterally-symmetrical wings332which are effectively extensions of the outer wall322. Each wing332interconnects the outer wall322and one of the side walls324,326. Each wing332has an aft edge334extending at an acute angle to the hole axis318. Collectively, the aft edges334of the two wings332form a “V”-shape with a concave curve336at its apex.FIG. 10shows only the exterior visible portions of the diffuser hole306, with the extent of the wings332(relative to the hooded area of a prior art diffuser hole) shown by dashed lines.

The diffuser section314includes a diffuser plug338extending radially outward from the inner wall320, centered on the hole axis318. The diffuser plug338includes an upstream face340, a downstream face342, and a pair of lateral faces344that extend axially between the upstream face340and the downstream face342. The lateral faces344are angled towards each other and meet at a radiused peak346. The downstream face342slopes aftward from the aft end of the peak346, to the inner wall320. The diffuser plug338terminates axially upstream of the aft end of the diffuser section314.

The diffuser plug338functions to decrease the expansion rate of flow through the diffuser section314by blocking some of the flow area of the diffuser section314. This is helpful in avoiding flow separation while still allowing a large covered area. Optionally, the diffuser holes306can be placed closer together so that they partially merge together. For example,FIG. 11shows a pair of diffuser holes306′ which are generally identical to the diffuser holes306described above, but the lateral spacing “S” between the two is selected such that the side wall326′ of one hole306′ merges with the side wall324′ of the adjacent diffuser hole306′. The merged side walls are displaced axially forward from the common outlet310′ of the diffuser holes306′. This configuration increases the lateral footprint coverage of the diffuser holes306′.

FIGS. 12 and 13illustrate a component wall400having another alternative diffuser hole406formed therein. The diffuser hole406is similar in construction to the diffuser hole106described above. Elements of the diffuser hole406which are not separately described may be considered to be identical to corresponding elements of the diffuser hole106. The diffuser hole406extends from an inlet408at the inner surface402of the component wall400to an outlet410at the outer surface404of the component wall400. The diffuser hole406includes a metering section412at its upstream end (cylindrical in this example), and a diffuser section414at its downstream end. The two sections412and414meet at a common junction plane416. A hole axis418extends coaxially to the metering section412.

The metering section412has an area (represented by diameter “D” in the case of a cylindrical shape) which is selected, in accordance with known practices, to provide a desired mass flow rate of cooling air, given specific pressure and velocity conditions upstream and downstream of the diffuser hole406. The diffuser section414expands in area axially aft (that is, the area at the outlet410is greater than at the junction plane416). Laterally, the diffuser section414is bounded by an inner wall420, an outer wall422, and a pair of side walls424,426. The four walls420,422,424, and426merge together into one continuous peripheral wall at the junction plane416.

The diffuser section414includes a diffuser pedestal448extending radially outward from the inner wall420, centered on the hole axis418. The diffuser pedestal448includes a generally wedge-shaped downstream face450which lies in plane with the outer surface404of the component wall400, and a pair of lateral faces452that extend axially forward from the downstream face450. The lateral faces452are angled towards each other and meet to form a leading edge454that extends from the downstream face450to the inner wall420. In the illustrated example, the leading edge454terminates aft of the aft edge456of the outer wall422.

The diffuser pedestal448effectively divides the aft portion of the diffuser section414into two separate legs458and460. The diffuser pedestal448functions similar to the diffuser plug338, slowing down the diffusion rate. It also functions to turn fluid flow in a more axial direction, i.e. parallel to the hole axis418. It is possible to vary the angle of each one of legs458,460.

Any of the diffuser holes106,206,306,406described above may be incorporated into a component wall in an arrangement suitable for a specific application, in accordance with known practices. For example, the diffuser holes may be used individually or arranged in one or more spanwise or oblique-extending rows on a component wall. Axially adjacent rows may be offset or interleaved with each other.

The diffuser holes described above may be formed in a component wall using various known machining processes, such as by using a laser machining process, an electrodischarge machining (EDM) process, a water jet machining process, a milling process and/or any other suitable machining process or combination of machining processes.

One known method is to provide an EDM tool (not shown) which represents the “positive” shape that forms one of the diffuser holes106,206,306,406. The EDM tool has a cylindrical portion that represents and forms the cylindrical metering section of the cooling hole, and a tapered portion that represents and forms the diffuser section.

Alternatively, the metering section of the diffuser hole may be formed in a separate manufacturing step from the diffuser portion of the diffuser hole. For example, the metering section may be initially formed within the component with the diffuser portion being subsequently machined therein or vice versa. This two-step method may be preferable where the diffuser hole does not provide a continuous line-of-sight along the hole axis, for example with the diffuser holes306and406having a plug and a pedestal, respectively. One suitable two-step process includes using an EDM tool to form the metering section, then to shape the diffuser section using a known low-power etching type of laser. This type of laser can be used to machine away material without forming a through-hole.

The diffuser holes described above have several advantages compared to prior art diffuser film cooling holes. The customized hole shape contouring results in improved effective hood length, larger footprint coverage, and better film flow attachment (i.e. reduced flow separation) from metering section to the end of the footprint. Side contouring of the diffuser holes creates better film flow vectoring relative to the gas flow. The hole shape and internal area variation suppresses flow separation due to internal shocks. The configurations that include diffuser plugs or pedestals are capable of wider diffusion angles because the internal feature reduces the flow area expansion of the hole before interaction with the gas stream.

The foregoing has described cooling hole structures for gas turbine engine components. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying potential points of novelty, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.