EP1113145B1 - Blade for gas turbines with metering section at the trailing edge - Google Patents

Description

TECHNICAL AREA

The present invention relates to the field of guide elements used in gas turbines, such as guide vanes or turbine blades. It relates to a guide element according to the preamble of claim 1.

STATE OF THE ART

A gas turbine comprises a plurality of elements, which are impinged by hot working air. Since the working air has a temperature which, for many of the materials from which such flow-around components are built, leads to severe wear and tear, especially with longer operating times, it is necessary to cool many of these components. The cooling can be designed as internal cooling, in which the elements are designed as hollow profiles or simply provided with internal cooling channels through which a cooling air flow is passed.

Alternatively or additionally, it is also possible to provide a so-called film cooling, in which the elements are subjected to an outside Kühlluftflim.

Modern gas turbine blades usually use a combination of the above methods, i. An internal convective cooling system is used, which additionally has openings for film blowing at critical points. In order to increase the efficiency and performance of the gas turbine, as well as to reduce emissions, the amount of cooling air used must be minimized. This means that even for large components only a small cooling air mass flow is available. In order to realize and control the low cooling mass flows with simultaneously required efficient internal heat transfer, the flow cross sections must be correspondingly reduced resp. Throttling cross sections are introduced.

In many of the known blade designs, the throttling of the cooling mass flow takes place in the region of the cast blade trailing edge, in the vicinity of the cooling air outlet. In particular, for manufacturing reasons, in order to avoid core fractures, the end of the ribs connecting the pressure and suction side walls is reset in the axial direction, i.e. the ribs already end inside the blade and do not reach the trailing edge.

Figure 1 shows a section through a prior art vane often used in gas turbines. It is an axial section to the main axis of the turbine and perpendicular to the blade plane extending through a vane, as they are typically used immediately after the combustion chamber and before the first run of the gas turbine for optimum flow of the blades. The blade is designed as a hollow profile, which is bounded on the suction side by a wall 10, and on the pressure side by a further wall 11. In the inflow region, the blade is widened, the walls 10 and 11 are connected in a rounding, and between the walls 10 and 11 is a central, radially extending insert 12, around which the cooling channel leads around. In the rear region of the guide vane 30 is limited only by the two with running in the axial direction, interrupted ribs interconnected walls 10 and 11, extending between cooling channels. Often, the central insert 12 is surrounded by approximately axially extending ribs in whole or in part. These ribs converge at the rear end of the insert (16 in Fig. 1) and connect from there to the suction and pressure side vane walls. Approximately axial channels are formed between the ribs, in which the cooling air is guided.

In the further course, the ribbed bench can be interrupted in order to produce a radial plenum 18. The subsequent ribbed bench 17 can be arranged both "in line" or offset from the previous ribbed bench. In the area of the trailing edge, the pressure- and suction-side walls are connected by very short ribs or so-called pin rows. The state of the art is now to let these internals (ribs, pins, etc.) inside the blade ends. This avoids that the core required for casting production has a large jump in the cross-sectional area exactly at the trailing edge. This strong discontinuity in Kemquerschnittsverlauf leads namely in the production of a high number of core breaks. However, the above method has the considerable disadvantage that the outlet cross section of the cooling air and thus the cooling air mass flow can only be controlled insufficiently.

The walls also mostly have film cooling holes 13-15, through which cooling air can flow to the outside.

• ◆ Da der Querschnitt klein ist, wirken sich selbst kleine Toleranzen bei der Herstellung (Guss) auf den Kühlluftmassendurchsatz der Schaufel aus.
• ◆ Da die Drosselstelle im Inneren des Leitelements liegt, lässt sich der wirksame Drosselquerschnitt nur schwer messen und kontrollieren.
• ◆ Da die Drosselkante im Inneren des Leitelements liegt, kann der wirksame Drosselquerschnitt nachträglich nur schwer modifiziert werden.
• ◆ Die beiden meist recht dünnen Wände sind äusserst anfällig auf Beschädigungen, welche von Fremdkörpern im Heissgas verursacht werden, und welche u.U. sogar zu einer Veränderung der Drosselquerschnitte führen können.
• ◆ Durch die stufenweise Expansion der Kühlluft (1) am Ende der Rippen und (2) an der Schaufelhinterkante lässt sich der Kühlluftmassenstrom nur schwer kontrollieren und justieren.

This design of the internal convective cooling system has a number of disadvantages:

• ◆ Since the cross section is small, even small manufacturing tolerances (casting) affect the cooling air mass flow rate of the blade.
• ◆ Since the throttle is located inside the baffle, it is difficult to measure and control the effective throttle area.
• ◆ Since the throttle edge is located inside the guide, the effective throttle area can be difficult to modify later.
• ◆ The two usually very thin walls are extremely susceptible to damage caused by foreign bodies in the hot gas, and which may even lead to a change in the throttle cross sections.
• ◆ The stepwise expansion of the cooling air (1) at the end of the ribs and (2) at the blade trailing edge make it difficult to control and adjust the cooling air mass flow.

In documents US-A-4,835,958, EP-A-0 924 383 and US-A-4,292,008, ribs reaching to the trailing edge are disclosed. In US-A-4,835,958, the ratios of the cooling steam flow are determined by internally located nozzles (128 in Fig. 6, 138 in Fig. 7), which are subsequently not changeable from the outside. The same applies to the internal impingement cooling holes 58, 59 in FIG. 1 of EP-A-0 924 383. In US-A-4,292,008, there are no statements as to the flow conditions with respect to the trailing edge slots 246 provided there (FIG. 8) and their subsequent change made.

In a further document US Pat. No. 5,243,759, finally, a method for changing the cooling flow conditions is specified, which refers to further inner parts (40, 44, 48) of a blade and proposes a complex change of the casting core, which only takes place during the next production process effects (see eg the abstract).

PRESENTATION OF THE INVENTION

The invention is therefore based on the object to improve a guide element of the type mentioned so that the cooling air flow can be changed by the guide element even after its preparation in a simple manner, and to provide a method for its preparation

This object is solved by the entirety of the features of claims 1 and 6. The essence of the invention is that the cooling air flow between the arranged at the trailing edge ribs can be much easier post-processing and maintenance due to good accessibility and maintenance, with the throttling causes the cooling air flow through the arranged at the trailing edge throttle ribs is, and the throttling from the outside easily by drilling or similar. set or can be measured.

An embodiment of the invention is characterized in that the thickness of the guide element at the trailing edge in the range of 0.5 to 5 mm, particularly preferably in the range of 1.0 to 2.5 mm, and that the slot thickness of the cooling air channels between the walls at the outlet in the range of 0.3 to 2 mm, in particular in the range of 0.8 to 1.5 mm. Among other things, if the guide element is designed as a guide blade arranged in front of a turbine rotor and if air is used as the cooling medium, the arrangement according to the invention and these dimensions prove to be particularly advantageous.

Further embodiments of the guide element emerge from the dependent claims.

In the method according to the invention, the casting core is shaped in such a way that the rib geometry is modeled beyond the trailing edge of the blade in the casting core. Only after a length of about 0.5 to 5, preferably 1 to 3 core thicknesses, the rib geometry is hidden. This method makes the simple production of a guide element according to the invention possible in the first place. In fact, in a normal casting process, the effective throat area can not simply be placed directly against the trailing edge. The erratic cross-sectional widening at the outlet in the Gusskem leads to a sharp increase in the core fractures during production. This can be avoided by leaving a supernatant in the casting process.

If any ribs are dispensed with in the region of the supernatant, core fractures can be largely avoided in the casting process, in particular in the case of the preferred investment casting process ("investment casting"). It is further shown that, especially if the length of the supernatant in the range of 0.5 to 3 times as large, particularly preferably the same size as slot thickness of the cooling air channel between the walls, such core fractures can be avoided without an excessive after manufacture Post processing would be necessary.

Further preferred embodiments of the method emerge from the dependent claims.

BRIEF EXPLANATION OF THE FIGURES

Fig. 1

zeigt einen Querschnitt durch eine Leitschaufel mit interner Kühlung für eine Gasturbine nach dem Stand der Technik; und

Fig. 2

a) zeigt einen Querschnitt durch eine Leitschaufel mit unmittelbar an der Hinterkante der Schaufel angeordneten Drosselrippen, b) eine Detailansicht des Hinterkantenbereichs des Schnittes nach a), und c) einen Schnitt entlang der Linie X-X in Figur 2a), d.h. im wesentlichen parallel zur Ebene der Schaufel durch den internen Kühlkanal.

The invention will be explained in more detail with reference to embodiments in conjunction with the drawings.

Fig. 1

shows a cross section through a guide vane with internal cooling for a gas turbine according to the prior art; and

Fig. 2

a) shows a cross-section through a stator blade with throttle ribs arranged directly at the trailing edge of the blade, b) a detail view of the trailing edge region of the section according to a), and c) a section along the line XX in FIG. 2a), ie substantially parallel to the plane the bucket through the internal cooling channel.

WAYS FOR CARRYING OUT THE INVENTION

Figure 2 a) shows a section through a vane with immediately adjacent to the trailing edge ribs 24 between the walls 10 and 11. It is a figure 2 corresponding, axially to the main axis of the turbine and perpendicular to the blade plane extending section through a vane. The blade is again designed as a hollow profile, which is bounded on the suction side by a wall 10, and on the pressure side by a further wall 11. In the rear region, the guide vane is limited only by the two walls 10 and 11 connected to one another with ribs interrupted in the radial direction, cooling channels run in between. FIG. 2c) shows a section along the line XX in FIG. 2a), ie substantially parallel to the plane of the page. Immediately adjacent to the insert 12 are first ribs 16. The cooling air flowing between insert 12 and the walls 10 and 11 flows substantially axially in the channels 27 between the ribs 16 in the rear portion of the vane. Behind the first row of ribs 16 is a front radial plenum 18, which allows a flow and pressure equalization of the cooling air in the radial direction. Thereafter, a further series of ribs 17 adjoin, which in this example are formed alternately as continuous ribs 17b or as axially divided ribs 17a. The individual ribs of the rows 16 and 17 advantageously have a so-called division ratio, the ratio of the radial width e normal to the plane of the sheet to the radial spacing f, in the range from 0.25 to 0.75.

This is followed by another radial plenum 19, followed by so-called pins 20, i. Formed as simple webs rows of ribs, which allow a uniform distribution of the cooling air flow at the trailing edge 21 as possible. The division ratio (diameter g to radial spacing h) of the pins 20 is in the range of 0.25 to 0.7.

• ◆ Der effektive Drosselquerschnitt kann leicht bei der Austrittskante gemessen werden.
• ◆ Es entsteht nur eine Drosselstelle genau na der Hinterkante anstatt zweier Drosselstellen am Ende der Rippen und der Hinterkante.
• ◆ Gegebenenfalls beim Gussverfahren entstandene Ungenauigkeiten der Drosselregion können leicht nachbearbeitet werden, da die Drosselstellen von aussen zugänglich sind.
• ◆ Der Drosselquerschnitt kann bei Bedarf leicht verändert werden.
• ◆ Die Anordnung der Rippen ganz am Ende der Schaufel führt zu einer erhöhten Stabilität der Abrisskante, so können Fremdkörper im Arbeitsluftstrom die Hinterkante weniger beschädigen und die Kühlung der Komponente kann durch derartige Deformationen weniger beeinträchtigt werden.

Immediately at the trailing edge and flush with this is now another series of ribs 24. The row of the rear ribs is dimensioned so that the throttling of the cooling air flow of the entire effective cooling channel cross section through the channels 25 between the so-called. Threads rib 24 is effected , By causing the throttling at the trailing edge 21 and with such a series of throttle ribs 24, there are a number of advantages:

• ◆ The effective throttle area can be easily measured at the trailing edge.
• ◆ Only one throttle point is created exactly along the trailing edge instead of two throttle points at the end of the ribs and the trailing edge.
• ◆ Any inaccuracies of the throttle region resulting from the casting process can be easily reworked as the throttle points are accessible from the outside.
• ◆ The throttle area can be easily changed if necessary.
• ◆ The arrangement of the ribs at the very end of the blade leads to increased stability of the spoiler lip, so foreign matter in the working air flow can damage the trailing edge less and the cooling of the component can be less affected by such deformations.

The production of such a blade is usually done by casting, usually a pressure casting process ("investment casting"). In these casting methods, however, the effective throttle cross-section can not simply be placed directly against the trailing edge during production. The sudden cross-sectional widening at the outlet in the casting core leads to a sharp increase in the core fractures during production. However, this can be avoided by leaving a supernatant in the casting process. The cooling geometry shown in the core is thereby extended beyond the actual limitation of the component. FIG. 2b) shows the edge region of an element which is extended over the trailing edge by the length b. In the region of the supernatant advantageously no ribs are arranged more. The transition from the throttle geometry then does not coincide with the core holder, but initially takes place within the extended component, a transition from the throttle geometry to a continuous radial channel, which can then be used without risk of broken core as a core holder. This transition can be optimally designed in different ways depending on the method to core holder, ie it is not mandatory that the two walls as shown in Figure 2b) are extended backwards evenly, for example, there are also a gradual protruding widening, or Rejuvenations resp. Thickening of the walls in the region of the supernatant conceivable. The projecting geometry is reworked after casting to the desired length of the trailing edge, ie removed, so that the throttle points coincide with the trailing edge. This can eg together with the usually subsequently necessary Post-processing such as erosion and laser drilling of the film cooling holes 13-15 happen.

In the specified embodiment, the trailing edge usually has a thickness d in the range of 0.5 to 5 mm, preferably in the range of 1.0 to 2.5 mm. The slot thickness c of the cooling air channel is usually in the range of 0.3 to 2.0 mm, preferably in the range of 0.8 to 1.5 mm. In order to be able to effectively avoid core fractures in the casting process, the supernatant b beyond the trailing edge should be 0.5 to 5 times, preferably 1 to 3 times, the length a of the throttle ribs 24, especially if the supernatant b is equal to the length a of the throttle ribs.

.BEZEICHNUNGSLISTE

10

suction-side wall

11

pressure-side wall

12

Use or core

13

suction-side film holes

14

Film holes at leading edge

15

pressure side film holes

16

on the insert subsequent ribs

17

intercostal

18

front radial plenum

19

rear radial plenum

20

pins

21

Trailing edge of the leaf

22

Outlet opening at the rear edge

23

Working air stream

24

Throttling ribs on trailing edge

25

Cooling air outlet openings at the rear edge

26

axial channels between ribs 17th

27

axial channels between ribs 16

28

inlet-side cooling air flow

29

exit-side cooling air flow

30

vane

a

Length of the throttle ribs

b

Length of the supernatant after casting

c

Slot thickness of the cooling air duct at the exit

d

Thickness of the vane at the trailing edge

e

Width of the throttle ribs

f

Rib division of the throttle ribs

G

Width of the pins 20

H

Division of the pins 20

Claims (10)

1. Gas-turbine guide element (30) around which a hot air flow (23) flows and which, at least in a trailing edge region (21), in which the air flow (23) separates from the guide element (30), comprises at least two walls (10, 11) arranged essentially in parallel and connected to one another by ribs (16, 17, 20), whereby internal cooling passages (18, 19, 25, 26, 27) are designed with an effective cooling passage cross-section, and which is cooled on the inside with cooling medium (28, 29) flowing through the cooling passages (18, 19, 25, 26, 27), the cooling medium discharging from the guide element (30) at the trailing edge (21) essentially parallel to and between the walls (10, 11), at least some of the ribs (24) being arranged so as to terminate essentially flush with the trailing edge (21) characterized in that a choke point for choking the cooling-medium flow of the entire effective cooling-passage cross section is provided at the trailing edge (21), and in that the row of ribs (24) terminating essentially flush with the trailing edge (21) is in this case dimensioned as choke ribs in such a way that the choking of the cooling-medium flow is effected by the cooling passages (25) between the ribs (24).
2. Guide element (30) according to Claim 1, characterized in that the choke ribs (24) have a width (e) parallel to the trailing edge (21) and are arranged at a distance apart by in each case a rib spacing (f), and in that the ratio of width (e) to rib spacing (f) is within a range of 0.25 to 0.75.
3. Guide element (30) according to one of the preceding claims, characterized in that the thickness (d) of the guide element (30) at the trailing edge (21) is within a range of 0.5 to 5 mm, in particular preferably within a range of 1.0 to 2.5 mm, and in that the slot thickness (c) of the cooling-air passages (25) between the walls (10, 11) at the outlet (21) is within a range of 0.3 to 2 mm, in particular within a range of 0.8 to 1.5 mm.
4. Guide element (30) according to one of Claims 1 to 3, characterized in that it is designed as a guide blade (30) arranged in front of a turbine rotor, and in that the cooling medium used is air.
5. Guide blade (30) according to Claim 4, characterized in that the guide blade is designed to be widened in its incident-flow region, and in the incident-flow region the cooling air flows in suction-side and pressure-side cooling passages around an inner, central, radially running insert (12), and in that the cooling air flows through between ribs (16) adjoining the insert (12), then between intermediate ribs (17), then between pins (20) between the walls (10, 11) before it discharges from the guide blade through outlet openings (25) at the trailing edge.
6. Method of producing a gas-turbine guide element (30) around which a hot air flow (23) flows and which, at least in a trailing edge region (21), in which the air flow (23) separates from the guide element (30), comprises at least two walls (10, 11) arranged essentially in parallel and connected to one another by ribs (16, 17, 20) in such a way as to form internal cooling passages (18, 19, 25, 26, 27), and which is cooled on the inside with cooling medium (28, 29) flowing through the cooling passages (18, 19, 25, 26, 27), the cooling medium discharging from the guide element (30) at the trailing edge (21) essentially parallel to and between the walls (10, 11), characterized in that the guide element (30) is produced by a casting process, in that the trailing edge region (21) is in this case cast with a projecting length extending the guide element (30) or its walls (10, 11) in the direction of flow, and in that the projecting length is removed after the casting in such a way that at least some of the ribs are arranged as choke ribs (24) so as to terminate essentially flush with the trailing edge (21).
7. Method according to Claim 6, characterized in that a choke point for choking the cooling-air flow of the entire effective cooling-passage cross section is provided at the trailing edge (21), and the row of ribs (24) terminating essentially flush with the trailing edge (21) is in this case dimensioned as choke ribs in such a way that the choking of the cooling-air flow is effected by the cooling passages (25) between the ribs (24) .
8. Method according to Claim 6 or 7, characterized in that the casting process is a pressure casting process, in that the projecting length has a value (b) behind the trailing edge (21), in that the walls (10, 11) are kept at a distance apart at the outlet (21) by a slot thickness (c) of the cooling-air passages (25), and in that in particular the projecting length value (b) is 0.5 to 5 times, in particular preferably 1 to 3 times, as large as the slot thickness (c).
9. Method according to one of Claims 6 to 8, characterized in that the choke ribs (24) have a width (e) parallel to the trailing edge (21) and are arranged at a distance apart by in each case a rib spacing (f), in that the ratio of width (e) to rib spacing (f) is within a range of 0.25 to 0.75, in that the thickness (d) of the guide element (30) at the trailing edge (21) is within a range of 0.5 to 5 mm, in particular preferably within a range of 1.0 to 2.5 mm, and in that the slot thickness (c) of the cooling-air passages (25) between the walls (10, 11) at the outlet (21) is within a range of 0.3 to 2 mm, in particular within a range of 0.8 to 1.5 mm.
10. Method according to one of Claims 6 to 9, characterized in that the guide element is a guide blade (30) arranged in front of a turbine rotor, and in that the cooling medium used is air.

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