WO2012028584A1

WO2012028584A1 - Turbine blade

Info

Publication number: WO2012028584A1
Application number: PCT/EP2011/064827
Authority: WO
Inventors: Hans-Thomas Bolms; John J. Marra
Original assignee: Siemens Aktiengesellschaft
Priority date: 2010-09-03
Filing date: 2011-08-29
Publication date: 2012-03-08
Also published as: EP2426316A1

Abstract

The invention relates to a turbine blade (1) for a gas turbine, comprising one after the other along a blade axis (11) towards a turbine blade tip (29), a platform region (13) and a airfoil (15) attached to said platform region, the airfoil (15) comprising an airfoil main body (12) and an airfoil tip shelf (17), the airfoil main body (12) comprises integrally formed a suction side wall (14) and a pressure side wall (16) bordering at least one cavity (37), wherein the cavity (37) is covered by said airfoil tip shelf (17), which is separately manufactured from the airfoil main body (12). In order to specify a turbine blade, in which improved cooling of the airfoil tip is provided and which is especially simple to produce for saving both time and costs, it is suggested that the suction side wall (14) and the pressure side wall (16) of the airfoil main body (12) both having a wall thickness (63) along its span direction, which in tip region (27) is constant.

Description

Description Turbine blade The invention relates to a turbine blade comprising a root region for attaching the turbine blade to a carrier, a platform region and an airfoil attached to said platform region, the airfoil comprising integrally formed a suction side wall and a pressure side wall extending from a common leading edge to a trailing edge and transversely from said platform region to a tip region bordering at least one cavity, wherein the cavity is covered by an airfoil tip shelf . In a gas turbine temperatures within the range of between

1000°C and 1800°C can occur in the flow duct when a working fluid in the form of hot gas is admitted to said gas turbine. Turbine blades which are exposed to the working fluid in order to absorb the kinetic energy of the latter are to be designed with regard to such loads. A turbine blade may be designed in the form of a moving blade fastened to a rotor. Furthermore, a turbine blade may be designed in the form of a guide blade firmly attached to the casing of a turbine.

Equally, in both blade types, in particular the tip of the turbine blade is subjected to high thermal loads. In a moving blade, there is also the high mechanical load caused by the rotary movement.

The external contour of the airfoil tip shelf is primarily determined by an aerodynamic definition of the object.

Furthermore, technical considerations relating to production are an important factor with regard to the shaping. In addition, a cooling design is relevant to the further

development of a turbine blade, and in this case in

particular the airfoil tip, as a result of the high thermal loads. This is because the tip must be cooled in order to achieve a long service life. Without cooling of the airfoil tip, it would rapidly oxidize. Nonetheless, the service-life requirements imposed on guide blades and in particular on moving blades are constantly increasing. That is to say that the component temperature must be kept within readily

acceptable limits through the use of a cooling fluid. In addition, in the cooling design of a turbine blade, in particular of a moving blade, in which in particular the design of the airfoil tip is relevant, the use of cooling fluid must be arranged efficiently in order to increase the overall efficiency and the output of a gas turbine.

To cool a turbine blade and in particular an airfoil tip, a number of measures have been proposed. To cool an airfoil in the form of a hollow profile, US 4,519,745 recommends a corrugated partition of the inner wall of the hollow profile. To cool an airfoil tip, a multiplicity of passages and an aperture in a bearing surface are provided for the airfoil tip, such that the airfoil tip can be cooled from outside with a cooling fluid transported via the passages and the aperture .

DE 198 131 15 Al discloses a cooled turbine blade of a gas turbine, the airfoil of which has a multiplicity of webs in the hollow profile, these webs serving as swirl elements. Furthermore, a shroud or blade-stiffening band is arranged on the end of the turbine blade. A cooling-air opening and a cooling-air outlet are connected to the hollow profile around this shroud. Furthermore, the shroud is deformed and has a narrow central section, such that this shroud becomes a lightweight shroud. In a similar manner, a multiplicity of shroud cooling openings are formed parallel to one another in such a way that a form is provided which enables the cooling air to be discharged outwards from the cooling-air outlet.

Furthermore, US 6,164,914 shows a turbine blade having a squealer tip.

It is also known to intensively cool a moving airfoil tip by holes being provided in the hollow profile of the airfoil tip itself in order to cool an airfoil tip shelf in the course of film cooling. In this case, a cooling fluid is forced out of the holes and settles in the form of a film on the outer surface of the hollow profile in a cooling manner. There is the problem in the abovementioned turbine blades that, on the one hand, the cooling of an airfoil tip can be arranged even more efficiently, but that, on the other hand, the cooling design of an airfoil tip, compared with the airfoil, is too complex for it to be produced advantageously from the

manufacturing technology point of view.

Besides these, FR 2 502 242 Al, US 2005 0091848 Al and EP 1 557 533 Al each teaches a modular turbine blade having a separately manufactured tip cap or tip insert at the free end of the airfoil section. In Detail both FR 2 502 242 Al and EP 1 557 533 A3 show each an impingement cooled tip region of the blades. However, both teach quite massive constructions of airfoils and tip caps increasing the mechanical load on the turbine blade during operation.

To increase the output and the overall efficiency of a gas turbine, a turbine blade in which the use of cooling medium can be arranged as efficiently as possible and which is also easier to produce would be desirable.

This is where the invention comes in, the object of which is to specify a turbine blade, in which improved cooling of the airfoil tip is provided and which is especially simple to produce for saving both time and costs.

The object is achieved by the invention by means of the turbine blade mentioned at the beginning, in which, according to the invention, the suction side wall of the airfoil main body and the pressure side wall of the airfoil main body both having a wall thickness along its span direction, which is in its tip region almost constant. In other words: the airfoil main body does not have at its tip region any projections extending transversely to the side walls. The invention is based on the knowledge, that the casting of the turbine blade or at least of its airfoil main body can be improved, if the outer end of the airfoil main body - the tip region - do not have any projections extending perpendicular to the pressure side wall and suction side wall. Due to the avoidance of the projections, the section side wall and the pressure side wall both having a wall thickness along its span direction, which in tip region is almost constant. This avoids an outer opening of the airfoil main body having a bottle neck - the outer opening of the airfoil main body is large as possible. Such an airfoil main body or a turbine blade having such an airfoil main body can be cast more easily with respect to precision, time and costs. Because of the big outer opening - also known as a core exit hole - in the blade tip region especially control of wall thickness and core position can be improved significantly.

The airfoil tip shelf is a cast and/or machine part

preferable from the same base material like the airfoil main body or the turbine blade. The bonding surfaces of the airfoil main body and the airfoil tip shelf are machined to allow a sufficient bonding and to stand up the thermal as well mechanical loadings.

The casting process for manufacturing the airfoil main body (itself or as a part of a turbine blade main body) is improved due to the totally open design of the tip region. After bonding both parts the airfoil main body and the airfoil tip shelf, the whole airfoil surface will be finished to prepare for metallic and/or ceramic oxidation and thermal protection coatings. The main advantage is the decreased complexity of casting, which improves the precision of the cast turbine blade with regard to wall thickness. The scrap rate can be lowered, which save time and costs. Furthermore, the free arrangement of film cooling holes in the airfoil tip shelf using

established bonding technologies improves the service- lifetime. Also an efficient tip cooling can be applied due to an easy access of the cavity. This can lead to a reduced thermal loading and less mass at the airfoil tip. The latter is mostly reached due to the avoidance of said perpendicular pro ections .

Further, the airfoil tip shelf comprises a shelf bottom, projections extending transversely from the shelf bottom and parallel to the side walls into the cavity and an impingement cooling plate spaced apart from said shelf bottom by said projections attached to the shelf bottom. The Projections arranged on the cold side of the shelf bottom acting as distance elements which will prevent buckling of the

impingement cooling plate due to the centrifugal force. The shelf bottom is cooled by impingement cooling air which is flowing through the impingement cooling openings arranged in the impingement cooling blade to the hot shelf bottom.

Advanced developments of the invention can be gathered from the sub claims and specify in detail advantage possibilities for configuring the turbine blade with regard to the cooling of the airfoil tip shelf with the whole series of further advantages over hitherto conventional measures.

In the first preferred embodiment the airfoil tip shelf is joined to the airfoil main body, the airfoil main body and the airfoil tip shelf being brazed or welded in place.

According to an advantageous development of the invention the airfoil tip shelf comprises at least one squealer tip

extending outwardly from the shelf bottom. In a preferred embodiment the squealer tip has a wall thickness thinner than the thickness of the pressure side wall or/and suction side wall. This leads to a reduced centrifugal loading in

comparison to conventional one-piece-casted airfoils. Using an impingement cooling plate has the advantage that the mass of the airfoil tip shelf can be kept as small as possible. Furthermore, it is possible to produce the airfoil and the airfoil tip shelf from different materials or same materials in order to be able to realize at the same time special advantages, such as, for example, low weight or high thermal conductivity of the airfoil tip shelf or, for

example, high strength of the airfoil.

In a further preferred embodiment the airfoil tip shelf and/or the tip region of the airfoil main body contain a number of cooling openings. The cooling openings are

advantageously formed and/or arranged as film cooling

openings, which, in cooling fluid is admitted to the turbine blade, enable a film of cooling fluid to be produced on the outer surface of the turbine blade. This allows additional cooling of thermal high loaded areas. The arrangement of the film cooling holes is very flexible, since the holes can be drilled from both the hot side as well as cold side of the shelf .

Fig. 1 shows a schematic illustration of a turbine blade, to which cooling fluid is admitted, on a rotor of a gas turbine,

Fig. 2 shows in a perspective sectional view a turbine blade having an airfoil main body and an airfoil tip shelf according to the preferred embodiment of the

invention .

Figure 1 shows a turbine blade 1 fastened to a rotor 3 of a gas turbine (not described in any more detail) . The turbine blade 1 in this case is one of a number of moving blades which are arranged in an annular manner extend radially in a flow duct 5 of the gas turbine and which in their entirety form a blade ring which extends into the annular cross section of the flow duct 5. A multiplicity of such annular blade rings are arranged along an axis 7 of the gas turbine (not described in any more detail) in the same way as the flow duct. A working fluid 9 in the form of a hot-gas mixture is admitted to the flow duct 5 and this hot-gas mixture expands, with the turbine blade 1 being driven, and thus delivers its kinetic energy, with the rotor rotating for driving a generator (not described in any more detail) .

The turbine blade 1 has - along a blade axis 11 arranged one after the other towards a turbine blade tip 29 - at least a platform region 13 and an airfoil 15. The airfoil 15

comprises an airfoil main body 12 arranged in the form of a hollow profile and an airfoil tip shelf 17 also arranged in the form of a hollow profile. The platform region 13

surrounds a blade platform for delimiting the flow duct 5 and a blade root, which are not shown in detail. The airfoil 15 comprises a suction side wall 14 and a pressure side wall 16 (FIG 2) . Both suction side wall 14 and pressure side wall 16 extend from a common leading edge 18 to a trailing edge 20 while surrounding a cavity 22 containing a passage system 19. As indicated schematically, a cooling fluid 21 can be

admitted to the turbine blade 1 via a passage system 19.

The cooling of the turbine blade 1 also extends in this case in particular to the airfoil main body 12 and the airfoil tip shelf 17.

Figure 2 shows in a perspective sectional view the embodiment according to the invention with regard to a tip region 27 of the turbine blade 1.

Whereas the concept of the invention explained above proves to be especially useful for the embodiments of a turbine blade 1 shown here, it should nonetheless be clear that the concept described can be equally realized within the scope of a turbine blade 1 of a gas or steam turbine and independently from their internal design of airfoil cooling. The airfoil main body 12 and the airfoil tip shelf 17 being produced separately. The airfoil main body 12 is usually produced by casting and designed as a hollow profile. The airfoil tip shelf 17 is - with regard to its cross-section - designed with shelf bottom 31, shoulders 33, spacers 34 and an impingement cooling plate 35. The shoulders 33 and spacers

34 are projections extending transversely from the shelf bottom 31 into the cavity 22. The impingement cooling plate

35 is spaced apart from the shelf bottom 31 by said shoulders 33 and spacers 34. The impingement cooling plate 35 is fixed to the shoulders 33 located close to the side walls 14, 16. The spacers 34 located between the shoulders 33 prevent buckling of the impingement cooling plate 35 due to

centrifugal forces occurring during operation of the turbine blade 1.

The hollow profile of the airfoil 15 contains the cavity 22 and the airfoil tip shelf 17 has a another cavity 37, which both are part of the cooling system 19 shown in Figure 1 and to which cooling fluid can be admitted. On its side facing the turbine blade tip 29, shown in Figure 1, the airfoil main body 12 has in its tip region 27 - in contrast to the turbine blade known from prior art - no wall running transversely to the blade axis 11. In other words: both the suction side wall 14 and the pressure side wall 16 having a wall thickness t along their span direction 11, which is also in the tip region 27 of the airfoil main body 12 almost constant. Hence, there exists no bottle neck between the suction side wall 14 and the pressure side wall 16 due to any casted perpendicular wall extensions.

The impingement cooling plate 35 and the shelf bottom 31 are opposite to one another forming a raised floor 45. By this raised floor 45 the other cavity 37 is formed between the impingement cooling plate 35 and the shelf bottom 31, which both extend horizontally over the entire cross section of the hollow airfoil main body 12. This leads to a reduced mass in comparison to known turbine blades, which having impingement cooling plates being at least partially casted together with the airfoil main body.

The thickness of the shelf bottom 31 is larger than the thickness of the impingement cooling plate, since the shelf bottom 31 has not only the objection to cover the cavity 22. Besides this, the shelf bottom 31 shall also enhance the mechanical rigidity of the airfoil 15. Due to this, the shelf bottom 31 is firmly connected by bonding, welding or brazing to the airfoil main body 12 directly and not via the

impingement cooling plate 35.

The raised floor 45 has cooling means, which are explained in detail below. In particular, impingement-cooling openings 43 are arranged in the impingement cooling plate 35. In

addition, the impingement cooling plate 35 is arranged so close to the shelf bottom 31 that an appropriately

pressurized cooling medium impinges on the shelf bottom 31 via the impingement-cooling openings 43 and effectively cools the airfoil tip shelf 17 in the course of impingement

cooling. This impingement cooling explained could be

intensified further by swirl elements (not shown) in the form of nipples and/or dimples arranged on the inner surface of the shelf bottom 31. That is to say that heat absorbed in the airfoil tip shelf is effectively dissipated by the cooling fluid as a result.

Further, in the present embodiment, the shelf bottom 31 has advantageously a number of first cooling openings 39 and second cooling openings 41, through which the cooling medium entered the other cavity 37 can be discharged out of the turbine blade 1. The first cooling openings 39 are inclined relative to the blade axis 11 to lead transversely cooling medium onto a surface of squealer tips 47 extending

perpendicular from the shelf bottom 31 outwardly. In addition, the shelf bottom 31 has a number of inclined second cooling openings 41 to enable a suitably film-cooling along the outer surfaces of the airfoil 15. In order to keep the mass of the airfoil tip shelf 17 to be cooled as small as possible, the squealer tips 47 and the shelf bottom 31 of the airfoil tip shelf 17 may be cast thinner than conventional one-piece casting practice would allow, providing reduced centrifugals loading on the airfoil walls 14, 16. Hence, the wall thickness 63 is smaller than the wall thickness t of the pressure side wall 16 and suction side wall 14. In addition, for the same reason, the wall structure of the airfoil tip shelf 17 can have higher porosity (not illustrated) than the wall structure of the airfoil 15.

In the turbine blade 1 shown provides a core exit hole 77 between the suction side wall 14 and the pressure side wall 16, which in this case is as large as possible. Since the demanding tip geometry, explained here, of the airfoil tip does not have to be cast together with the airfoil main body 12, the casting of the turbine blade 1 is simplified saving both time and cost. The connection between airfoil tip shelf 17 and airfoil main body 12 is produced in the joining region 60 in this case by an especially suitable welding, brazing or bonding process. The connecting surfaces between airfoil tip shelf 17 and airfoil main body 12 in the joining region 60 can be produced in an especially simple and precise manner. The core exit hole 77 is closed in the course of a specifically sized fitting of the airfoil tip shelf 17 onto the core exit hole 77. The contact area of the connection can then be further extended, when the projection 34 contacts the inner surfaces of their side walls 14, 16 respectively. In summary the invention relates to a turbine blade (1) for a gas turbine, comprising one after the other along a blade axis (11) towards a turbine blade tip (29), a platform region

(13) and a airfoil (15) attached to said platform region, the airfoil (15) comprising an airfoil main body (12) and an airfoil tip shelf (17), the airfoil main body (12) comprises integrally formed a suction side wall (14) and a pressure side wall (16) bordering at least one cavity (37), wherein the cavity (37) is covered by said airfoil tip shelf (17), which is separately manufactured from the airfoil main body

(12) . In order to specify a turbine blade (1), in which improved cooling of the airfoil tip is provided and which is especially simple to produce for saving both time and costs, it is suggested that the suction side wall (14) and the pressure side wall (16) of the airfoil main body (12) both having a wall thickness (63) along its span direction, which in tip region (27) is constant.

Claims

Patent claims

Turbine blade (1) for a gas turbine,

comprising one after the other along a blade axis (11) towards a turbine blade tip (29) ,

a root region for attaching the turbine blade (1) to a carrier,

a platform region (13) and

a airfoil (15) attached to said platform region, the airfoil (15) comprising an airfoil main body (12) and an airfoil tip shelf (17),

the airfoil main body (12) comprises integrally formed a suction side wall (14) and a pressure side wall (16) extending from a common leading edge (18) to a trailing edge and transversely from said platform region (13) to a tip region (27) bordering at least one cavity (37), wherein the cavity (37) is covered by said airfoil tip shelf (17), which is separately manufactured from the airfoil main body (12),

characterized in that

the suction side wall (14) of the airfoil main body (12) and the pressure side wall (16) of the airfoil main body (12) both having a wall thickness (63) along its span direction, which in tip region (27) is at least nearly constant, and

wherein the airfoil tip shelf (17) comprises

a shelf bottom (31),

shoulders (33) and/or spacers (34) extending transversely from the shelf bottom (31) into the cavity (37) and

an impingement cooling plate (35) spaced apart from said shelf bottom (31), attached to said shoulders (33) and/or spacers (34) .

Turbine blade (1) according to claims 1,

wherein the airfoil tip shelf (17) is joined to the airfoil main body (12), the airfoil main body (12) and the airfoil tip shelf (17) being brazed or welded in place .

3. Turbine blade (1) according to claims 1 or 2,

wherein the airfoil tip shelf (17) comprises at least one squealer tip (47) extending outwardly.

4. Turbine blade (1) according to claim 3,

wherein the squealer tip (47) has a wall thickness (63) thinner than the thickness (t) of the suction side wall

(14) and/or the thickness (t) of the pressure side wall

(16)

5. Turbine blade (1) according to one of the proceeding

claims ,

wherein the airfoil tip shelf (17) and/or the tip region (27) contain a number of cooling openings (39) .

6. Turbine blade (1) according to claim 5,

wherein the cooling openings (39) are formed and/or arranged as film cooling openings, which, when cooling fluid is admitted to the turbine blade (1), enable a film of cooling fluid (21) to be produced on the outer surface the airfoil.