Extended length holes for tip film and tip floor cooling

The tip cooling arrangement of the present application reduces large cooling flow requirements which can compromise turbine performance. The tip cooling arrangement of the present application provides convective cooling of a turbine blade tip end, whether a flat tip or a squealer, by extending holes that provide fluid for film cooling the tip end. The holes are thus lengthened and extend from the relatively cooler suction side of the blade to the pressure side of the blade in close proximity to the floor of the tip end.

FIELD OF THE INVENTION

This invention is directed generally to turbine blades and, more particularly, to an arrangement for cooling the tip end of a turbine blade by conducting cooling fluid from an inner cavity through elongated holes that extend from proximate a suction side of the blade to cooling orifices in the pressure side of the blade. The holes are positioned so that cooling fluid passing from the cavity through the elongated holes cools the tip end during its passage and is discharged from the cooling orifices to mix with and cool hot gas before it passes over the tip end, which can be a flat tip or a squealer.

BACKGROUND OF THE INVENTION

Typically, gas turbine engines include a compressor for compressing air, a combustor for mixing the compressed air with fuel and igniting the mixture, and a turbine blade assembly for producing power. Combustors often operate at high temperatures that may exceed 2,500 degrees Fahrenheit. Typical turbine combustor configurations expose turbine blade assemblies to these high temperatures. As a result, turbine blades must be made of materials capable of withstanding such high temperatures. In addition, turbine blades often contain cooling systems for prolonging the life of the blades and reducing the likelihood of failure as a result of excessive temperatures.

The blade tip region is an area of particularly high thermal stress which is exposed to high heat load due to high external heat transfer coefficients in this region and ineffective convective cooling due to its geometry. Migration of mid-span hot gas to the blade tip region also contributes to the problem. Typical blade designs, illustrated inFIG. 1by a sectional view of a blade100having a pressure side102and a suction side104, rely on extensive film cooling to reduce the gas temperature in contact with the blade tip end106. Common film cooling arrangements use one row of holes108on the pressure side102of the blade100just below the tip end106, illustrated inFIG. 1as a squealer having a rail110defining a squealer cavity112, and several rows of holes114through the floor116of the squealer cavity112of the tip end106. The large number of film holes108,110requires a large amount of cooling air flow which may compromise the performance of the gas turbine.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, a turbine blade comprises a generally elongated blade having a leading edge, a trailing edge, a pressure side and a suction side. A tip is located at a first end of the elongated blade and a root is coupled to the elongated blade at a second end generally opposite the first end. The root supports the elongated blade and couples the elongated blade to a disc. A cooling system includes at least one inner cavity in the elongated blade and further comprises at least one elongated cooling hole having a first end in communication with the inner cavity proximate the suction side of the elongated blade and a second end defining a cooling orifice in the pressure side of the elongated blade. The elongated cooling hole is positioned so that cooling fluid passing from the cavity through the elongated cooling hole cools the tip and is discharged from the orifice on the pressure side of the elongated blade to mix with and cool hot gas before it passes over the tip.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIG. 2, an exemplary turbine blade120for a gas turbine engine is illustrated. The blade120includes an elongated blade122and a root124which is used to conventionally secure the blade120to a rotor disk of the engine for supporting the blade120in the working medium flow path of the turbine where working medium gases exert motive forces on the surfaces of the elongated blade122. The elongated blade122has an outer wall126that surrounds at least one inner cavity128(FIG. 3). The outer wall126comprises a generally concave pressure side130and a generally convex suction side132which are spaced apart in a widthwise direction to define the inner cavity128therebetween. The pressure and suction sides130,132extend between and are joined together at an upstream leading edge134and a downstream trailing edge136. The leading and trailing edges134,136are spaced axially or chordally from each other. The elongated blade122extends radially along a longitudinal or radial direction of the blade120, defined by a span of the elongated blade122, from a radially inner platform138to a radially outer blade tip140.

Referring additionally toFIGS. 3-5, a cooling system for the blade120comprises the inner cavity128in the elongated blade122and at least one elongated cooling hole142having a first end144in communication with the inner cavity128proximate the suction side132of the elongated blade122and a second end146defining a cooling orifice148in the pressure side130of the elongated blade122, the elongated cooling hole142being positioned so that cooling fluid passing from the cavity128through the elongated cooling hole142convectively cools the tip140and is discharged from the orifice148on the pressure side130of the elongated blade122to mix with and cool hot gas before it passes over the tip140. The at least one elongated cooling hole142can be formed in the tip140, for example in the floor150of a squealer cavity152of the tip140of the elongated blade122. The cooling arrangement of the present application can also be used for turbine blades having flat tips.

The at least one elongated cooling hole142defines a substantially linear axis154between the first and second ends144,146of the at least one elongated cooling hole142. The axis154is oriented at a first angle, within a range of about 0 degrees to about 20 degrees (FIG. 3), relative to inner and outer surfaces of the tip140, for example the floor150of the squealer cavity152and the inner surface156of the inner cavity128, and is oriented at a second angle, for example from about 20 degrees to about 90 degrees relative to the exit surface130E of the pressure side130of the elongated blade122(FIG. 4). The second angle is currently contemplated as being within a range of 40 degrees to 50 degrees, and, for example, at an angle of 45 degrees. The cooling orifice148may comprise a conventional diffuser film hole158wherein the diffuser film hole is fanshaped, laidback or is both fan-shaped and laidback as illustrated.

To adequately cool the tip of the turbine blade120, the at least one elongated hole142in the elongated blade122comprises a plurality of elongated cooling holes142. The floor of the tip140, i.e., the floor150of the squealer cavity152as illustrated inFIG. 3, further comprises at least one slot160extending radially into the inner surface156of the floor150, and extending longitudinally in a cordal direction. The at least one slot160is proximate the suction side132of the tip140and at least one of the plurality of holes142is in fluid communication with the inner cavity128via the at least one slot160. A plurality of slots160, for example the slots160athrough160cas illustrated inFIG. 4, can also be used. In particular, the plurality of slots160a,160band160cmay each be associated with a respective cavity passage128a,128band128cof the inner cavity128, as may be seen inFIG. 5.

FIG. 6is an exploded view of an elongated blade122ashowing two alternative embodiments for constructing the turbine blade120including a flat blade tip140aand a squealer tip140b. The tips140a,140binclude a leading edge162, a trailing edge164, a pressure side166, a suction side168, an outer surface170and an inner surface172. The plurality of elongated cooling holes142can be formed in the tip140a,140bor in the elongated blade122aitself. Alternately, as shown inFIG. 7, the floor150may comprise a cooling plate174with the plurality of elongated cooling holes142being formed in the cooling plate174and the cooling plate174being positioned between and secured to the first end of the elongated blade122aand the tip140, illustrated as a squealer end140b, to form the elongated blade122.

As noted above, the elongated blade122comprises a pressure side130and a suction side132. The pressure and suction sides130,132define an outer wall of the elongated blade122, and the outer wall defines the inner cavity128as a cooling fluid passage within the elongated blade122. The cooling fluid passage extends from a location proximate the second end to the first end of the elongated blade122to convey cooling fluid in a spanwise direction through the elongated blade122to the first end of the at least one elongated cooling hole142. The cooling fluid passage may extend through a plurality of passages such as the cavity passages128a,128band128cillustrated inFIG. 5.

As illustrated, the tip140comprises a partition member, i.e., the floor150, between the inner cavity128and the squealer cavity152defined by a squealer rail153extending radially from the outer wall, and the at least one cooling hole142extends through the partition member from the first end144, positioned at a junction between the inner cavity128and the suction side132, to the second end146at the pressure side130. The at least one elongated cooling hole142comprises a plurality of elongated cooling holes142defining a plurality of cooling orifices148in the pressure side130of the elongated blade122. The plurality of cooling orifices148comprises a plurality of diffuser film holes.

From the foregoing description, it should be apparent that the tip cooling arrangement of the present application reduces large cooling flow requirements which otherwise can compromise the performance of a gas turbine. The cooling flow reduction contrasts with the large amount of cooling air flow for extensive film cooling required for tip cooling in typical prior art blade designs having a large number of film holes. The tip cooling arrangement of the present application provides convective cooling of a turbine blade tip end, whether a flat tip or a squealer, by extending the holes that provide fluid for film cooling the tip end. The holes are thus lengthened to extend from the relatively cool suction side of the blade to the pressure side of the blade in close proximity to the floor of the tip end.

The row of pressure side film cooling holes142is drilled into the tip at an angle of from 0 degrees to 20 degrees and is fed cooling fluid through one or more slots near the suction side of an inner cooling cavity. The film cooling holes142are also angled at from about 20 degrees to about 90 degrees relative to the exit surface130E of the pressure side130of the elongated blade122. The angling of the cooling holes142relative to the exit surface130E produces long cooling holes142through which cooling fluid passes prior to film ejection. The plurality of long cooling holes142extracts a significant amount of heat from the tip surface before ejection into the free-stream on the pressure side of the blade. By convectively cooling the floor150of the tip end140, film holes through the tip end are not required thus reducing the cooling mass flow requirement.

The long cooling holes142can use diffuser exits to improve film coverage on the pressure side of the blade. While film coverage on the pressure side of the blade may be lower than the typical film cooling arrangement, the reduction in coverage should be small and can be further reduced by selection of the film hole diffuser shapes. The addition of convective cooling through the long holes will significantly improve the blade tip cooling capability and improve life of the tip region.

Additionally, the tip cooling arrangement of the present application is more practical from a manufacturing standpoint as well as from a service repair standpoint. The arrangement can be produced using current manufacturing processes for casting and hole drilling. Also, during service repair for damaged blade tips, the disclosed arrangement will make it easier to rebuild the tip through welding in case of tip parent metal loss.