TURBINE BLADE FOR A GAS TURBINE

Abstract

A turbine blade for a gas turbine is provided. The quantity of coolant flowing off the rear edge thereof is set relatively simply and exactly directly upon casting the turbine blade, without reworking the cast turbine blade with respect to the setting of coolant consumption being necessary. Raised areas are situated on the inner surfaces of the intake side wall or pressure side wall, between which a throttle element is present, by means of which the quantity of coolant flowing out is set. This arrangement allows a core tool to be produced simply, by means of which the casting cores required for casting the turbine blade are produced having the desired precision in great quantities.

Description

FIELD OF INVENTION

The invention relates to a turbine blade comprising a main blade part, around which a hot gas can flow and which comprises a suction-side wall and a pressure-side wall which extend in the direction of flow of the hot gas from a common leading edge to a trailing edge, wherein at least one opening for blowing out a coolant which cools the main blade part beforehand is arranged on the trailing edge, which at least one opening is fluidically connected to a cavity arranged in the main blade part by means of a channel, wherein the channel is also delimited by an inwardly facing face of the suction-side wall and by an inwardly facing face of the pressure-side wall and a throttling element is provided for setting the quantity of coolant emerging from the opening.

BACKGROUND OF INVENTION

A turbine blade of the type mentioned in the introduction and a casting core for producing such a turbine blade are known, for example, from WO 2003/042503 A1. The known turbine blade has a cooled trailing edge, on which a plurality of openings for blowing out the cooling air are separated from one another by interposed webs (also known as “tear drops”). A common cavity is arranged upstream of the openings arranged on the trailing edge, in which cavity there are three rows of pillar-like pedestals (also known as “pin fins”), which are provided for increasing the transfer of heat of the cooling air which brushes past them and for increasing the pressure loss there.

FIG. 7 of WO 2003/042503 A1 shows a perspective illustration of the casting core required for producing such a turbine blade. The space occupied by the casting core remains, after the cast turbine blade has been produced, as a cavity in the turbine blade, with openings arranged in the casting core being filled with casting material. In this respect, the casting core represents the negative reflection of the interior of the turbine blade.

The pin fins known from WO 2003/042503 A1 have a cylindrical shape and connect the inner faces of the suction-side wall and pressure-side wall, which are located opposite one another, of the main blade part of the turbine blade.

In this context, it is known to set the quantity of cooling air emerging at the trailing edge of the turbine blade by a suitable selection of the maximum pressure loss and/or the smallest cross-sectional area close to the trailing edge through which the cooling air is to flow. However, this procedure can lead to casting cores in which the openings provided on the casting core trailing edge become so large that only still relatively thin separating webs remain between them. During handling of the casting core, however, the casting core can fracture precisely at this point, and therefore it then becomes unusable.

Furthermore, WO 2003/042503 A1 discloses C-shaped guide elements for cooling air, which are arranged in turning regions of cooling channels and which are intended to bring about low-loss deflection and guidance of the cooling air in downstream zones.

Furthermore, EP 1 091 092 A2 discloses an air-cooled turbine blade. In order to achieve particularly efficient cooling of a hollow-walled suction or pressure side of the main blade part, pins are arranged in grid form in the cavity of the double wall. In principle, the pins are diamond-shaped, with the corners thereof being rounded off and the edges thereof being curved concavely inward. Between the pins, a network of passages therefore arises for cooling air, these passages each having a narrowed inlet opening and a narrowed outlet opening, between which there is a diffuser and nozzle portion.

The portions are intended to be used to decelerate and accelerate the cooling air in order to achieve the efficient cooling.

Furthermore, U.S. Pat. No. 5,752,801 discloses an internally cooled turbine blade, the cooling channels of which on the trailing edge side are configured with a zigzag shape by cast-in c-shaped fins. A better cooling action can thereby be achieved. In addition, the casting cores required for the production can thereby be stiffened.

SUMMARY OF INVENTION

It is therefore an object of the invention to provide a turbine blade of the type mentioned in the introduction for a gas turbine, which can be cooled efficiently and sufficiently using the smallest quantity of coolant possible.

The object relating to the turbine blade is achieved by a turbine blade according to the features of the claims, with advantageous solutions being presented in the claims.

The turbine blade for a gas turbine comprises a main blade part, around which a hot gas can flow and which comprises a suction-side wall and a pressure-side wall which extend in the direction of flow of the hot gas from a common leading edge to a trailing edge, wherein at least one opening for blowing out a coolant which cools the main blade part beforehand is arranged on or in the trailing edge, which at least one opening is fluidically connected to a cavity arranged in the main blade part by means of a channel, wherein the channel is also delimited by an inwardly facing face of the suction-side wall and by an inwardly facing face of the pressure-side wall and a throttling element is provided for setting the quantity of cooling air emerging from the opening, wherein, according to the invention, the throttling element is arranged upstream—in relation to the throughflow direction of the channel—of the opening in question and comprises two elevations which are each arranged on one of the two inwardly facing faces.

In other words: the throttling element comprises elevations which are arranged on the inwardly facing faces and which extend transversely to the throughflow direction of the channel, and between which there is arranged the minimum throughflow cross section of the channel. To determine the minimum throughflow cross section, it is necessary to detect the minimum perpendicular distance between respective fibers of the neutral fibers of the coolant flow and one of the two side faces in the cooling channel.

The invention is based on the recognition that the coolant consumption can be set in a particularly simple and exact manner using the proposed design by arranging the throttling element upstream of the trailing edge opening in the interior of the blade. In this case, the throttling element is to be formed by two elevations placed in relation to one another, of which one is arranged on the inwardly facing face of the suction-side wall and one on the inwardly facing face of the pressure-side wall. Neither of the elevations connects the suction-side wall to the pressure-side wall. This embodiment of the throttling element is particularly advantageous for turbine blades produced by a casting process. It is known that turbine blades are mostly produced by casting processes, in which so-called lost casting cores are used to produce the inner cooling system. These casting cores are produced mostly with the aid of a core die. The core die comprises two slider elements, which can be moved toward one another and away from one another. When pushed together, these slider elements surround a cavity, which has the same contour as the cavity of the turbine blade to be cast. To produce the casting core, the casting core material is introduced into the cavity of the slider elements. After the casting core material has dried, the casting core is available for producing the turbine blade.

According to the invention, the slider elements are designed, for producing a first prototype of the turbine blade series to be produced, in such a way that, in the turbine blade prototype to be produced, the throttling, minimum distance between the elevations is in any case smaller than that required in theory. The first turbine blade prototype thus produced is then subjected to a coolant flow rate measurement. As desired, on account of the distance between the elevations being initially too small, the throttling action is too great, which for the time being leads to an excessively small flow rate. Depending on the result of the flow rate measurement, the slider elements are then modified. The elevations thereof are modified slightly, as a result of which the minimum distance therebetween increases when pushed together. Then, a further casting core is produced therewith. This is used to produce a further turbine blade prototype, the flow rate of which is then determined again and compared with the desired rate. If the flow rate determined corresponds to the desired flow rate, the process for producing the slider elements is concluded. The slider elements are then formed in such a way that casting cores with which appropriate turbine blades can be produced in series are always produced with them. If the most recently determined flow rate does not correspond to the desired flow rate, all steps are carried out again for producing a further turbine blade prototype with a minimum distance which is increased somewhat compared to the preceding prototype.

The particular advantage of the proposed solution is that each of the two sliders can be machined on their own—for instance by grinding the elevation arranged thereon—without fundamentally changing the structure of the turbine blade and the cooling system thereof. It is possible in this respect for only one of the slider elements or else both slider elements to be machined during one iteration step.

This method is also suitable particularly in the case of modifications to already existing blades in the case where more cooling air is needed for sufficient cooling. In this case, only extremely small modifications are needed to the blade design. An additional qualification owing to an otherwise required change in casting is therefore not necessary.

In this case, the two elevations are arranged offset in relation to one another—as seen in the throughflow direction of the cooling channel. The offset arrangement makes it possible for the perpendicular distance between the inner face of the pressure-side wall and the inner face of the suction-side wall to be reduced further, which leads to particularly narrow trailing edge regions of main blade parts. This reduces aerodynamic losses in the hot gas flowing around the main blade part.

As a whole, the invention leads to a reduction in the reject rate during the production of turbine blades, which significantly improves the production costs and the production time for turbine blades.

It is advantageous that that elevation which is arranged on the inwardly facing face of the pressure-side wall is arranged downstream of that elevation which is arranged on the inwardly facing face of the suction-side wall. This design enforces a flow of coolant in the channel which flows in an intensified manner past the inwardly facing face of the suction-side wall. This makes it possible, particularly in the case of the so-called cut-back trailing edges, to achieve a lengthened film cooling action of the unprotected end of the suction-side trailing edge, which reduces wear phenomena there and lengthens the service life of the turbine blade.

It is preferable that a plurality of openings are arranged on the trailing edge, the cooling channel collectively connecting a plurality of openings to the cavity. If the elevations are in the form of fins, it is also possible for turbulences to be generated in the coolant during operation with the aid of this angular contour of the inwardly facing faces of the side walls of the main blade part. These turbulences can contribute firstly to the throttling action and secondly to an increase in the transfer of heat on account of a more turbulent coolant flow.

The interior of the turbine blade as proposed by the invention can be employed both for turbine blades having a common (for the side walls) trailing edge and for turbine blades having a so-called cut-back trailing edge.

BRIEF DESCRIPTION OF THE DRAWINGS

A further advantageous embodiment of the invention will be explained in more detail with reference to the drawing, in which:

FIG. 1 shows a perspective illustration of a turbine rotor blade,

FIG. 2 shows a longitudinal section through the region of the trailing edge of the turbine rotor blade known from the prior art,

FIG. 3 shows a cross section through the trailing edge region of a turbine blade according to the invention according to a first configuration, and

FIG. 4 shows a cross section through the trailing edge region of a turbine blade according to the invention according to a second configuration.

The same features are provided with identical reference signs in all the figures.

DETAILED DESCRIPTION OF INVENTION

FIG. 1 is a perspective illustration of a gas turbine blade 10 relating to the invention. According to FIG. 1, the gas turbine blade 10 is in the form of a rotor blade. The invention can also be used in a guide vane (not shown) of a gas turbine. The turbine blade 10 comprises a blade root 12, with a fir tree-like cross section, and also a platform 14 arranged thereon. An aerodynamically curved main blade part 16 adjoins the platform 14 and comprises a leading edge 18 and also a trailing edge 20. Cooling openings arranged as a so-called “shower head” are provided on the leading edge 18, from which cooling openings an internally flowing coolant, preferably cooling air, can emerge. The main blade part 16 comprises a—with respect to FIG. 1—rear-side suction-side wall 22 and also a front-side pressure-side wall 24. A multiplicity of openings 28 separated from one another by interposed webs 30 are provided along the trailing edge 20. In this case, the trailing edge 20 is in the form of a so-called cut-back trailing edge, and therefore the openings 28 lie more on the pressure side than in the center of the trailing edge 20.

FIG. 2 shows the interior of a turbine blade known from the prior art in a longitudinal section along a plane, spanned by a center line, which extends from the leading edge 18 to the trailing edge 20 of the main blade part 16, and by the longitudinal direction of the blade, which extends from the blade root 12 toward the blade tip.

In FIG. 2, the trailing edge openings 28, between which the webs 30 are arranged, are shown arranged further to the right. The webs 30 extend substantially parallel to a flow of hot gas which, during operation, flows around the main blade part 16 from the leading edge 18 to the trailing edge 20. Shown on the left in FIG. 2, a multiplicity of pillars or pedestals 32 arranged in a grid are provided. In this case, both the pedestals 32 and the webs 30 extend from an inner face 34 of the suction-side wall 22 to an inner face (not shown in FIG. 2) of the pressure-side wall 24. Consequently, the pedestals 32 are arranged in a cavity 38 of the turbine blade 10, which is laterally delimited by the suction-side wall 22 and the pressure-side wall 24.

If the turbine blade 10 is used in a gas turbine, a coolant, for example cooling air 40 or cooling steam, flows through the cavity 38 during operation. The part of the turbine blade 10 which is not shown in FIG. 2 is generally internally designed such that the field of pedestals 32 is subjected to a substantially uniform incident flow of cooling air 40. The uniform incident flow onto the pedestals 32 arranged in the grid is shown by the arrows marked with 40. The cooling air 40 impinges on individual pedestals 32 and, in the process, is deflected by these, with the main direction of flow of said cooling air remaining substantially unchanged. Turbulences are thereby produced in the cooling air 40. The heat introduced by the hot gas into the blade walls 22, 24 is thereby conducted further into the pedestals 32, where the cooling air 40 impinging on the pedestals 32 absorbs the heat and carries it away. Once the cooling air 40 has flowed through the field of pedestals, it enters passages 41 which connect the cavity 38 to the openings 28. Once it has flowed through the passages 41, the cooling air 40 passes out of the turbine blade 10 through the openings 28 and blends with the hot gas flowing around the main blade part 16.

In order here to set the quantity of coolant leaving the openings 28, elevations 42, 44 (FIG. 3, FIG. 4) are provided on the inner faces 34, 36 of the suction-side wall 22 and pressure-side wall 24. One (42) of the two elevations 42, 44 is arranged on the inner face 34 or part thereof, and the other (44) of the two elevations 42, 44 is situated on the inner face 36 or part thereof. The inner faces 34, 36 delimit a cavity 38 and also a cooling channel 46, which connects the cavity 38 to the openings 28. In this respect, it is possible for the cavity 38 and channel 46 to merge into one another. According to the invention, the minimum distance between the inner face 34 and the inner face 36 is then provided in the region of the two elevations 42, 44. In this respect, what is shown is the neutral fiber 47—in FIG. 3 in relation to the cross section shown therein through the trailing edge 20 of the turbine blade 10 of the cooling channel 46 which is always at the same perpendicular distance from the inner face 34 and the inner face 36. The minimum distance A forming the throttling element is situated here between the two elevations 42, 44, as a result of which the latter are in relation to one another.

The elevations 42, 44 replace neither the pedestals 32 nor the webs 30.

As shown in FIG. 3, the elevations 42, 44 extend along the longitudinal direction of the blade (perpendicular to the plane of the sheet) over the entire height of the cooling channel 46. The contours of the elevations 42, 44 are configured, as in the cross section shown in FIG. 3, such that they make a continuous and edge-free profile of the cooling channel possible in the direction of flow of the coolant toward the trailing edge opening 28. Here, the cooling channel 46 converges. Alternatively, it may be provided that the elevations are also in the form of fins, as shown in FIG. 4.

As shown in FIG. 4, the elevations 42, 44 have a fin-like contour with a height H₁ and H₂, respectively.

During the production of a first prototype of the turbine blade according to the invention, the heights H₁ and H₂ are relatively large, and therefore it is possible to determine a coolant consumption which lies below the desired or predefined consumption. By modifying the core die, i.e. the corresponding slider elements, it is possible to successively produce further prototypes which, on account of reduced fin heights H₁, H₂, always consume slightly more coolant than the prototype produced before. Each iteration in this case includes the production of a turbine blade having a defined fin height H₁ and H₂ and the determination of the coolant consumption of the corresponding turbine blade prototype. As soon as a coolant consumption corresponding to the desired or predefined quantity is established, the production of the slider elements is ended, and therefore the core die which is then available can be used to produce casting cores and therefore turbine blades with the desired coolant consumption to an increased extent, which significantly reduces the reject rate.

De facto, the proposed configuration provides a turbine blade 10 which, during the phase of die production, makes a simple and cost-effective test phase possible, in order to provide a core die produced exactly for a series of turbine blades 10 after the conclusion of the iterations.

Furthermore, it is even possible that the casting cores required to cast the turbine blade 10 according to the invention fracture less frequently upon handling than the casting cores known from the prior art.

It is of course also possible for the throttling element to comprise only a single elevation 44 (or 42) instead of two elevations 42, 44, such that the minimum distance which determines the flow rate is situated between a single elevation 44 (or 42) and the then inwardly directed face 34 (or 36) of the suction-side wall 22 (or of the pressure-side wall 36) which lies opposite it. In this case, the opposing face 34 or 36 can then also have a planar configuration in the region of the minimum distance.

Overall, the invention specifies a turbine blade 10, the quantity of coolant 40 of which flowing out from the trailing edge 20 is set relatively simply and exactly immediately upon casting of the turbine blade 10, without it being necessary to rework the cast turbine blade 10 in terms of setting the coolant consumption. In order to achieve this, it is proposed that elevations 42, 44 are situated on the inner faces 34, 36 of the suction-side wall 22 and pressure-side wall 24, between which elevations the throttling element used to set the quantity of coolant flowing out is located. This arrangement makes it possible to simply produce a core die with which the casting cores required for casting the turbine blade 10 can always be produced in large quantities with the desired accuracy.

Claims

1-6. (canceled)

7. A turbine blade for a gas turbine, comprising: a main blade part, around which a hot gas flows and which comprises a suction-side wall and a pressure-side wall which extend in the direction of flow of the hot gas from a common leading edge to a trailing edge,wherein an opening for blowing out a coolant which cools the main blade part beforehand is arranged on the trailing edge, which opening is fluidically connected to a cavity arranged in the main blade part by means of a channel,wherein the channel is also delimited by an inwardly facing face of the suction-side wall and by an inwardly facing face of the pressure-side wall and a throttling element is provided for setting the quantity of coolant emerging from the opening,wherein the throttling element comprises two elevations, upstream in relation to the throughflow direction of the channel, of the opening, which are arranged offset in relation to one another, as seen in the throughflow direction of the cooling channel, and between which there is arranged the minimum throughflow cross section of the channel, andwherein the two throttling elements are each arranged each on one of the two inwardly facing faces.

8. The turbine blade as claimed in claim 7, wherein a first elevation which is arranged on the inwardly facing face of the pressure-side wall is arranged downstream of a second elevation which is arranged on the inwardly facing face of the suction-side wall.

9. The turbine blade as claimed in claim 7, wherein a plurality of openings are arranged on the trailing edge and the cooling channel collectively connects a plurality of openings to the cavity.

10. The turbine blade as claimed in claim 7, wherein the elevations are in the form of fins.

11. The turbine blade as claimed in claim 7, wherein the cooling channel converges and the two elevations are situated on the inwardly facing faces with a continuous and edge-free profile.

12. The turbine blade as claimed in claim 9, wherein the plurality of openings are provided on the pressure wall side.