Film cooling structure and turbine blade for gas turbine engine

The film cooling structure includes a wall part and a cooling hole inclined such that an outlet is positioned rearward of an inlet. The cooling hole includes a straight-tube part and a diffuser part. The diffuser part includes a flat surface, a curved surface curved rearward and forming, together with the flat surface, a semicircular or semi-elliptical channel cross section larger than that of the straight-tube part, a first section and a second section extending from the first section toward the outlet. In the first section, an area of the channel cross section increases as it approaches the outlet. In the second section, the area of the channel cross section increases as it approaches the outlet at an increase rate smaller than that of the first section or is constant. The diffuser part has a width equal to or twice greater than the depth of the diffuser part.

BACKGROUND

1. Technical Field

The present disclosure relates to a film cooling structure and a turbine blade for a gas turbine engine.

2. Description of the Related Art

A turbine of a gas turbine engine includes turbine blades that constitute stator vanes and turbine blades. The turbine blades are exposed to combustion gas from the combustor. To prevent thermal damage due to the combustion gas, a number of film cooling holes are formed on an airfoil surface of each turbine blade (see Japanese Patent No. 5600449 and Japanese Patent Laid-Open Application Publication No. 2013-124612).

SUMMARY

To improve the efficiency of the gas turbine engine, it is important to increase the temperature of combustion gas (combustion temperature). With the increase of combustion temperature, further improvement is required in the cooling efficiency of the turbine blade.

The present disclosure has been made with the above consideration, is objected to provide a film cooling structure and a turbine blade for a gas turbine engine, which are capable of improving cooling efficiency.

A first aspect of the present disclosure is a film cooling structure including: a wall part having an outer surface and an inner surface and extending forward and rearward; a cooling hole penetrating through the wall part, including an inlet opening to the inner surface and an outlet opening to the outer surface, and being inclined such that the outlet is positioned rearward of the inlet; wherein the cooling hole includes a straight-tube part having the inlet, and a diffuser part connecting with the straight-tube part and having the outlet, the diffuser part includes: a flat surface; a curved surface curved rearward and forming a channel cross section together with the flat surface, the channel cross section having a semicircular or semi-elliptical shape larger than that of the straight-tube part; a first section in which an area of the channel cross section increases as the channel cross section approaches the outlet of the cooling hole; and a second section in which an area of the channel cross section increases at an increase rate or is constant as the channel cross section approaches the outlet of the cooling hole, the second section extending from the first section toward the outlet of the cooling hole, and the increase rate being smaller than that in the first section, the straight-tube part is positioned inside the diffuser part on a projection plane of the cooling hole orthogonal to an extending direction of the cooling hole, and the diffuser part has a length along the flat surface on the projection plane equal to or twice greater than a of the diffuser part along a direction orthogonal to the flat surface on the projection plane.

The diffuser section may include a third section positioned between the straight-tube part and the first section. The third section may extend between the straight-tube part and the first section with a cross section of the same shape as the cross section of the first section at a position closest to the straight-tube part.

The flat surface of the diffuser part may be offset forward of an inner peripheral surface of the straight-tube part on the projection plane.

On the projection plane, the flat surface of the diffuser part may be located forward of a central axis of the straight-tube part by a distance same as a distance from the central axis to a forefront portion of the inner peripheral surface of the straight-tube part, the portion being located forefront.

The curved surface of the diffuser part may include a first recess extending to the outlet of the cooling hole. The first recess may be located on each of both sides of the straight-tube part in a direction along the flat surface of the diffuser part on the projection plane.

The curved surface of the diffuser part may include a second recess extending to the outlet of the cooling hole. The second recess may be located rearmost on the projection plane.

A second aspect of the present disclosure is a turbine blade for a gas turbine engine including the film cooling structure according to the first aspect of the present disclosure.

The present disclosure can provide a film cooling structure and a turbine blade for a gas turbine engine, which are capable of improving cooling efficiency.

DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present disclosure will be described with reference to the drawings. Components common in respective drawings are denoted by the same reference numerals, and the description to be duplicated thereof will be omitted.

The film cooling structure according to the present embodiment is provided on a structure exposed to a high-temperature heat medium (for example, combustion gas). The structure may be, for example, a turbine blade (rotor blade and stator vane) of a gas turbine engine (not shown), a combustor liner, a nozzle of a rocket engine, or the like. A large number of cooling holes are formed in a wall part of the structure. The cooling holes constitute a film cooling structure together with the wall part. The cooling medium CG (e.g., air) flowing out of the cooling holes forms a heat insulating layer on the wall part to protect the structure from the heat medium. Hereinafter, for convenience of explanation, the upstream side in the flow direction of the heat medium HG is defined as “forward (front)” and the downstream side in the flow direction of the heat medium HG is defined as “rearward (rear)”.

First Embodiment

A first embodiment of the present disclosure will be described.FIG.1is a top view illustrating a cooling hole (cooling channel)30in a film cooling structure10according to the present embodiment.FIG.2is a cross-sectional view illustrating the film cooling structure10according to the present embodiment.FIG.3is a diagram (projection view) illustrating an example of the cooling hole30on a projection plane orthogonal to the extending direction of the cooling hole30. This projection view shows the relative positions of the straight-tube part33described later and the diffuser part34described later, and respective channel cross sections (in other words, contours). Hereinafter, the “projection plane” is interpreted as a projection plane of the cooling hole30orthogonal to an extending direction of the cooling hole30(in other words, the central axis P).

As shown inFIG.2, the film cooling structure10includes the wall part20and the cooling hole30. The wall part20has an inner surface21and an outer surface22. The wall part20extends forward and rearward. The outer surface22is exposed to a heating medium HG and the inner surface21faces a cooling medium CG. The material of the wall part20may be a known heat-resistant alloy.

The cooling hole30includes an inlet31opening to the inner surface21and an outlet32opening to the outer surface22. The cooling hole30penetrates through the wall part20and is inclined such that the outlet32is positioned rearward of the inlet31. In other words, the cooling holes30extend from the inner surface21to the outer surface22at an angle inclined toward a flow direction of the heat medium HG with respect to a thickness direction TD of the wall part20. The cooling medium CG flows into the inlet31and flows out from the outlet32.

As shown inFIG.1, the cooling hole30includes a straight-tube part33and a diffuser part34. The straight-tube part33has the inlet31of the cooling hole30and extends along a central axis P from the inlet31to a connection portion35connected with the diffuser part34. The extending direction of the central axis P is also the extending direction of the entire cooling hole30.

An inner peripheral surface36of the straight-tube part33defines a channel cross section (cross section)33A. The shape of the channel cross section33A is constant over the extending direction of the straight-tube part33. As shown inFIG.3, the channel cross section33A has a shape of, for example, a circle around the central axis P as the center. However, the channel cross section33A of the straight-tube part33may be an ellipse, a triangle, a rectangle, or the like.

Like the straight-tube part33, the diffuser part34also extends along the central axis P. The diffuser part34communicates (connects) with the straight-tube part33and has the outlet32of the cooling hole30. That is, the diffuser part34extends along the central axis P from the connection portion35with the straight-tube part33to the outlet32of the cooling hole30.

As shown inFIG.3, the diffuser part34includes a flat surface37and a curved surface38, which are formed as an inner peripheral surface of the diffuser part34. The flat surface37is positioned forward of the central axis P of the straight-tube part33and extends along the central axis P of the straight-tube part33to the outer surface22of the wall part20.

On the projection plane, the flat surface37of the diffuser part34is located forward of the central axis P of the straight-tube part33by a distance same as a distance from the central axis P to a forefront portion36aof the inner peripheral surface36of the straight-tube part33.

For example, when the inner peripheral surface36of the straight-tube part33is curved forward, the flat surface37coincides with the tangent plane of the curved inner peripheral surface36. In this case, the flat surface37has a portion connected to the inner peripheral surface36without having a step with the inner peripheral surface36.

The curved surface38of the diffuser part34is positioned rearward of the flat surface37. The curved surface38extends from the connection portion35to the outer surface22of the wall part20(the outlet32of the cooling hole30) while curving rearward. As shown inFIG.3, the curved surface38, together with the flat surface37, forms a channel section (a channel cross section34A of the diffuser part34) having a semicircular or semi-elliptical shape. The curved surface38and the flat surface37are connected to each other via fillets39. The fillet39is a minute curved surface for smoothly connecting between the curved surface38and the flat surface37.

The diffuser part34includes a first section40and a second section41. The second section41extends from the first section40toward the outlet32of the cooling hole30. As illustrated by the channel cross section40B, the area of the channel cross section40A (seeFIG.3) in the first section40increases as it approaches the outlet32of the cooling hole30. In other words, the first section40of the diffuser part34is flared toward the outlet32of the cooling hole30.

In the second section41, the area of the channel cross section41A is constant. In other words, the second section41of the diffuser part34extends toward the outlet32of the cooling hole30while having the same channel cross section as the largest channel cross section in the first section40.

The area of the channel cross section41A in the second section41may increase as the channel cross section41A approaches the outlet32of the cooling hole30at an increase rate smaller than that in the first section40. In other words, the second section41may expand (enlarge) more gradually than the first section40toward the outlet32of the cooling hole30.

Here, for convenience of explanation, the curved surface38in the first section40is referred to as the first curved surface38a, and the curved surface38in the second section41is referred to as the second curved surface38b. That is, the inner peripheral surface in the first section40is composed of the first curved surface38aand the flat surface37, and the inner peripheral surface in the second section41is composed of the second curved surface38band the flat surface37.

As shown inFIG.2, the distance between the flat surface and the central axis P of the straight-tube part33is substantially constant. On the other hand, the distance between the first curved surface38aand the central axis P increases as the first curved surface38aapproaches the outlet32of the cooling hole30. That is, the channel cross section40A in the first section40expands rearward as the channel cross section40A approaches the outlet32of the cooling hole30. The distance between the second curved surface38band the central axis P is constant or increases at an increase rate smaller than that in the first section40as it approaches the outlet32of the cooling hole30.

As described above, the flat surface37and the curved surface38(i.e., the first curved surface38aand the second curved surface38b) form a channel cross section34A having a semicircular shape.FIG.3shows channel cross sections40A,40B, and41A as one example. The channel cross section40A is a cross section of the first section40at a position closest to the straight-tube part33in the first section40, and is also a channel cross section of the connection portion35. The channel cross section41A is a cross section of the second section41. The channel cross section40B indicated by the dotted line is a cross section of the first section40at any position between the connection portion35and the second section41.

On the projection plane shown inFIG.3, the entire straight-tube part33is located inside the diffuser part34. That is, the channel cross section34A of the diffuser part34is larger than the channel cross section33A of the straight-tube part33. Therefore, the inner peripheral surface36of the straight-tube part33and the inner peripheral surface (i.e., flat surface37and curved surface38) of the diffuser part34form a stepped surface35aat the connection portion35between the straight-tube part33and the diffuser part34. That is, the inner peripheral surface (at least curved surface38) of the diffuser part34is connected to the inner peripheral surface36of the straight-tube part33via a stepped surface35a(seeFIG.1).

The stepped surface35aextends in a direction crossing the extending direction of the cooling hole30. That is, the stepped surface35amay extend from an edge of the straight-tube part33in a direction orthogonal to the extending direction of the cooling hole30, or may extend in a direction inclined with respect to the extending direction of the cooling hole30.

For convenience of explanation, the direction along the flat surface37on the projection plane shown inFIG.3is referred to as the width direction WD. A direction orthogonal to a direction along the flat surface37on the projection plane is defined as a depth direction (height direction) DD. In this embodiment, the length (width) of the diffuser part34in the width direction WD is equal to or twice greater than the length (depth, height) of the diffuser part34in the depth direction DD. For example, the width Lw1of the channel cross section40A is set to a value equal to or twice greater than the depth (height) Ld1of the channel cross section40A. Similarly, the width Lw2of the channel cross section41A is set to a value equal to or twice greater than the depth (height) Ld2of the channel cross section40A. The cross-sectional shape of the diffuser part34at other locations also has the same dimensional relationship. Accordingly, the channel cross section34A of the diffuser part34has a semicircular shape that is elongated in the direction along the flat surface37(i.e., the width direction WD).

FIG.4is a diagram illustrating a flow of the cooling medium CG in the cooling hole30according to the first embodiment. In the figure, the main stream of the cooling medium CG is shown by a solid line. As shown in this figure, the main stream of the cooling medium CG flows from the straight-tube part33to the diffuser part34. The flow path of the cooling hole30extending from the inlet31starts to expand rearward at the connection portion35. With this expansion of the flow path, the main stream of the cooling medium CG is separated from the curved surface38and flows toward the outlet32of the cooling hole30while maintaining the state thereof.

Because of the separation described above, a secondary flow50of the cooling medium CG is generated. The secondary flow50flows in the same direction as the main stream of the cooling medium CG in a space near the main stream of the cooling medium CG, but flows in the opposite direction to the main stream of the cooling medium CG in a space far from the main stream of the cooling medium CG. That is, the secondary flow50forms a vortex (secondary vortex)51shown inFIG.4.

The secondary flow50in the second section41generally flows in a direction from the flat surface37toward the second curved surface38b. On the other hand, as described above, the second curved surface38bextends in the extending direction of the cooling hole30with an inclination angle smaller than that of the first curved surface38a. Consequently, as compared with a case where the first curved surface38awould extend until the outlet32of the cooling hole30, more secondary flow50can be deflected to the straight-tube part33.

The secondary flow50toward the straight-tube part33flows along the first curved surface38a, narrows the main stream of the cooling medium CG narrows in the depth direction DD and spreads it in the width direction WD. That is, the film cooling air spreads in the width direction to enhance the film cooling efficiency. In addition, since the cooling medium CG is not excessively accelerated or decelerated, the speed difference between the accelerated cooling medium CG and the main stream of the heat medium is reduced. Consequently, it is possible to suppress an aerodynamic loss (pressure loss) caused by mixing of the cooling medium CG and the heating medium HG when the cooling medium CG flows out of the outlet32of the cooling hole30.

Because of the expansion of the channel cross section in the diffuser part34and the separation of the main stream of the cooling medium CG, another vortex (secondary vortex)52is generated in the diffuser part34in addition to the vortex51as described above. The vortex52is generated in the vicinity of the connection portion35and on both sides of the straight-tube part33in the width direction WD. The vortex52rotates about an axis parallel to the extending direction of the cooling hole30and causes aerodynamic loss. However, as described above, the secondary flow50, which forms the vortex51, flows from the curved surface38of the diffuser part34toward the flat surface37of the diffuser part34in the vicinity of the connection portion35. The secondary flow50attenuates the vortex52traveling to the outlet32of the cooling hole30.

The main stream of the cooling medium CG spreads (expands) in the width direction WD of the cooling hole30in accordance with the compression thereof by the secondary flow50. In addition, the vortex52causing the aerodynamic loss is attenuated as it travels to the outlet32. Therefore, according to the film cooling structure of the present embodiment, the film cooling can be widely performed with suppressing the aerodynamic loss. That is, the cooling efficiency with the cooling medium CG can be improved.

Second Embodiment

Next, a second embodiment of the present disclosure will be described.FIG.5is a top view illustrating the cooling hole according to the second embodiment.FIG.6is a diagram (projection view) showing an example of the cooling hole30according to the second embodiment on a projection plane. FIG.7is a diagram illustrating a flow of the cooling medium CG in the cooling hole30according to the second embodiment. As shown inFIG.5, the diffuser part34according to the second embodiment includes a third section42positioned between the straight-tube part33and the first section40of the diffuser part34. The inner peripheral surface of the third section42includes a third curved surface38cbeing a part of the curved surface38and the flat surface37. Other configurations of the second embodiment are the same as those of the first embodiment.

The third section42extends between the straight-tube part33and the first section40with a channel cross section42A having a constant shape. The channel cross section42A has the same shape as the channel cross section40A at a position closest to the straight-tube part33in the first section40. With the formation of the third section42, the stepped surface35ais formed between the straight-tube part33and the third section42.

As described above, in the diffuser part34, a vortex52, which may cause aerodynamic loss, is generated in the vicinity of the connection portion35. In the present embodiment, the vortex52is generated mainly in the third section42and travels toward the outlet32of the cooling hole30. On the other hand, the secondary flow50, which forms the vortex51, flows toward the third section42in the vicinity of the first curved surface38ain the first section40, and then flows in a direction from the first curved surface38atoward the flat surface37. The secondary flow50flowing toward the flat surface37merges (collides) with the vortex52to prevent the travel of the vortex52and attenuate it.

The formation of the third section42expands a region in which the secondary flow50attenuates the vortex52. The secondary flow50also expands a region where the main stream of the cooling medium CG is compressed. Accordingly, the acceleration of the main stream of the cooling medium CG can be promoted, thereby the aerodynamic loss can be further suppressed.

Here, for convenience of explanation, an aspect ratio of the diffuser part34is defined. The aspect ratio is a value obtained by dividing the length (width) of the diffuser part34in the width direction WD by the length (depth, height) of the diffuser part34in the depth direction DD.

As shown inFIG.6, the aspect ratio (Lw3/Ld3) of the third section42may be larger than the respective aspect ratios (Lw1/Ld1and Lw2/Ld2) of the first section40and the second section41. That is, the third section42may have a flatter shape in the width direction WD than those of the first section40and the second section41.

Third Embodiment

Next, a third embodiment of the present disclosure will be described.FIGS.8A and8Bare diagrams (projection views) illustrating examples of the cooling hole30according to the third embodiment on the projection plane.FIG.8Ais a diagram illustrating a first example thereof, andFIG.8Bis a diagram illustrating a second example thereof.FIGS.9A and9Bare sectional views each illustrating a film cooling structure10according to the third embodiment.FIG.9Ais a cross-sectional view illustrating a first example thereof, andFIG.9Bis a sectional view illustrating a second example thereof.FIGS.9A and9Billustrate the flow of the cooling medium CG in the cooling hole30.

The diffuser part34shown inFIG.8Ais a modification of the first embodiment and includes the first section40and the second section41. The diffuser part34shown inFIG.8Bis a modification of the second embodiment and includes the first section40, the second section41and the third section42.

The flat surface37of the diffuser part34according to the third embodiment is offset forward of the inner peripheral surface36of the straight-tube part33on the projection plane of the cooling hole30. Therefore, a stepped surface35ais interposed between the flat surface37and the inner peripheral surface36. The other configuration of the third embodiment is the same as that of the first and second embodiments.

Also in the third embodiment, the secondary flow50, which forms the vortex51, flows along the first curved surface38atoward the straight-tube part33. The secondary flow50compresses the main stream of the cooling medium CG at the connection portion35and its periphery. On the other hand, as described above, the flat surface37of the third embodiment is offset forward of the straight-tube part33. Accordingly, the main stream of the cooling medium CG is deflected forward while being compressed by the secondary flow50. Accordingly, the acceleration of the main stream of the cooling medium CG and the dispersion of the main stream in the width direction WD are promoted.

Fourth Embodiment

Next, a fourth embodiment of the present disclosure will be described.FIG.10is a diagram (projection view) illustrates an example of the cooling hole30according to the fourth embodiment on a projection plane. In the fourth embodiment, at least one of the first recess43and the second recess44is provided on the second curved surface38bof the second section41. Other configurations of the fourth embodiment are the same as those of the first to third embodiments.

For convenience of explanation,FIG.10illustrates only the straight-tube part33and the second section41. As shown in this figure, the first recess43is located on each of both sides of the straight-tube part33in a direction along the flat surface37of the diffuser part34on the projection plane (i.e., the width direction WD). The first recess43is curved in a direction separating from the central axis P. The first recess43has a curvature radius sufficiently smaller than that of the second curved surface38band extends to the outlet32of the cooling hole30. The flat surface37of the diffuser part34may be inclined or curved to be widened toward the outlet32. In other words, the flat surface37may be inclined or curved relative to the central axis P such that the closer the flat surface37is to the outlet32, the farther it is from the central axis P. The angle between this inclined surface or curved surface (tangent plane thereof) and the outer surface22(outlet32) increases toward the outlet32.

The second recess44is positioned at the rearmost part of the second curved surface38bon the projection plane. Same as the first recess43, the second recess44is also curved in a direction separating from the central axis P (i.e., rearward) with a curvature radius sufficiently smaller than that of the second curved surface38band extends to the outlet32of the cooling hole30. Here, both the first recess43and the second recess44may extend from a predetermined position in the second curved surface38bto the outlet32, or may extend from the first curved surface38aof the first section40to the outlet32. A part of the second curved surface38bmay have a tapered surface tapered rearward and in the width direction WD.

According to an analysis of the present disclosure, the cooling efficiency by the cooling medium CG can be improved by forming at least one of the first recess43and the second recess44on the second curved surface38b.

It should be noted that the first to third embodiments can apply the aforementioned inclination of the flat surface37with respect to the central axis P or curvature of the flat surface37with respect to the central axis P (i.e., replacement of the curved surface).

Fifth Embodiment

Next, a fifth embodiment of the present disclosure will be described. The fifth embodiment of the present disclosure is a turbine blade for a gas turbine engine, which applies a film cooling structure10according to any one of the first to fourth embodiments. A stator vane60as the turbine blade together with the rotor blade (not shown) constitutes a turbine (not shown) of a gas turbine engine (not shown). The film cooling structure10may be applied to the rotor blade as the turbine blade, as similar to the stator vane60.

FIG.11is a perspective view illustrating a schematic configuration of the stator vane60. As shown in this figure, the stator vane60includes an airfoil61, bands62, and cooling holes30. The airfoil61is provided on the downstream side of a combustor (not shown) which discharges the combustion gas as the aforementioned heating medium HG. That is, the airfoil61is located in a flow path of the combustion gas.

The airfoil61has a leading edge61a, a trailing edge61b, a pressure surface (pressure side)61c, and a suction surface (suction side)61d. Combustion gas as the heating medium HG flows in the direction from the leading edge61ato the trailing edge61balong the pressure surface61cand the suction surface61d.

The airfoil61is provided with an internal space (cavity or cooling channel (not shown)) into which cooling air as a cooling medium CG is introduced. The cooling air is extracted from a compressor (not shown), for example. The bands62are provided to sandwich the airfoil61in a span direction SD of the airfoil61. The bands62function as a part of a wall of the flow path of the combustion gas (i.e., endwalls, platforms or shrouds). These bands62are integrated with the tip and the hub of the airfoil61.

In this embodiment, the film cooling structure10is applied to at least one of the pressure surface61cand the suction surface61dof the airfoil61. That is, at least one of the pressure surface61cand the suction surface61dof the airfoil61functions as the wall part20of the film cooling structure10, and the cooling holes30are formed therein. Hereinafter, for convenience of explanation, an example in which the film cooling structure10is provided on the pressure surface61cwill be described.

The cooling hole30penetrates through the pressure surface61cand is inclined such that the outlet32is positioned closer to the trailing edge61bthan the inlet31. The flat surface37of the diffuser part34extends in the extending direction of the cooling hole30and in the span direction SD of the airfoil61.

In the pressure surface61c, the main stream of the combustion gas flows in a direction from the leading edge61atoward the trailing edge61b. On the other hand, the cooling air, which has been introduced into the airfoil61, flows into the inlet31of the cooling hole30and flows out of the outlet32. The cooling air, which has flown out of the outlet32, flows downstream while merging with the main stream of the combustion gas. While exiting the outlet32, the cooling air is expanded in the span direction SD. Therefore, the cooling area on the pressure surface61ccan be extended in the span direction SD.

In addition, the cooling air is accelerated until it flows out of the outlet32. Thus, the speed difference between the main stream of the cooling air and the main stream of the combustion gas is reduced, thereby aerodynamic loss can be suppressed. That is, it is possible to provide a turbine blade capable of performing film cooling of a wide area while suppressing aerodynamic loss.

It should be noted that the present disclosure is not limited to the embodiments described above, but is indicated by the description of the claims and further includes all modifications within the meaning and scope of the description of the claims.