Cooled blade for a gas turbine

Information

  • Patent Grant
  • 6379118
  • Patent Number
    6,379,118
  • Date Filed
    Friday, January 12, 2001
    24 years ago
  • Date Issued
    Tuesday, April 30, 2002
    22 years ago
Abstract
In a cooled blade for a gas turbine, a cooling fluid, preferably cooling air, flows for convective cooling through internal cooling passages located close to the wall and is subsequently deflected for external film cooling through film-cooling holes onto the blade surface. The fluid flow is directed in at least some of the internal cooling passages in counterflow to the hot-gas flow flowing around the blade. Homogeneous cooling in the radial direction is achieved by providing a plurality of internal cooling passages and film-cooling holes arranged one above the other in the radial direction in the blade in such a way that the discharge openings of the film-cooling holes in each case lie so as to be offset from the internal cooling passages, and in particular the discharge openings lie between the internal cooling passages.
Description




The present invention relates to the field of gas turbine technology. It concerns a cooled blade for a gas turbine, where the blade has internal cooling passages located close to the wall of the blade. Cooling fluid such as air flows for convective cooling through the internal cooling passages and is subsequently deflected for external film cooling through film-cooling holes onto the blade surface.




BACKGROUND OF THE INVENTION




To increase the output and the efficiency, ever increasing turbine inlet temperatures are used in modem gas-turbine plants. In order to protect the turbine blades from the increased hot-gas temperatures, these blades have to be cooled more intensively than was necessary in the past. At high turbine inlet temperatures, both convective cooling and film-cooling elements are used. In order to increase the effectiveness of these types of cooling, it is desirable to reduce the wall-material thicknesses. Furthermore, optimum distribution between convective heat absorption of the cooling fluid and cooling-fluid temperature during the blow-out as a cooling film is desired.




Combinations of convective cooling and film cooling at reduced wall thicknesses have been disclosed, for example, in various publications including WO 99/06672, and patents U.S. Pat. No. 5,562,409, U.S. Pat. No. 4,770,608, and U.S. Pat. No. 5,720,431. In the disclosures, the convective cooling is carried out via impingement cooling, only a small part of the surface being cooled by the respective cooling-fluid jet, which is subsequently used for the film cooling. The convective cooling capacity of the fluid is therefore only partly utilized.




Patents U.S. Pat. No. 5,370,499 and U.S. Pat. No. 5,419,039 describe a method of avoiding this disadvantage. In this case, the cooling fluid is first used for convective cooling in passages close to the wall before it is blown out as a film. At the same time, the convective cooling passages may be provided with turbulence increasing devices (ribs, cylinders or crossed passages). However, the cooling fluid is always directed in these devices in parallel with the main-gas flow, which does not constitute the best solution for optimum cooling.




In the publication WO-Al-99/06672 mentioned above, it has been proposed to direct the cooling fluid in the convective part in an antiparallel manner i.e. in counterflow to the main-gas flow (and thus to the film-cooling flow). This results in cooling which is more homogeneous in the axial direction or in the direction of the hot-gas flow. However, it is still questionable whether homogeneous cooling or temperature distribution in the radial direction is achieved.




SUMMARY OF THE INVENTION




In one aspect of the invention, a cooled gas-turbine blade is provided, which also ensures a homogeneous distribution of the material temperature of the blade in the radial direction.




The turbine blade includes a plurality of internal cooling passages and film-cooling holes arranged one above the other in the radial direction of the blade, with the discharge openings of the film-cooling holes being offset from the internal cooling passages, and in particular, the discharge openings of the film-cooling holes lie between the internal cooling passages.




A plurality of internal cooling passages and film-cooling holes are arranged one above the other in the radial direction of the blade in such a way that the discharge openings of the film-cooling holes in each case lie so as to be offset from the internal cooling passages, and in particular lie between the internal cooling passages. Since the cooling effect of the film cooling between the holes is less than in the axial direction downstream of the holes, the cooling effect of the internal cooling is utilized in these intermediate regions by the arrangement according to the invention.




The cooling fluid is first directed in counterflow to the hot-gas flow in convective passages close to the wall, which are integrated in the overall structure and can be provided with turbulence-generating devices that affect the flow of the cooling fluid before the cooling fluid is used for film cooling. As a result, very uniform temperature distributions are produced, which is very important for the small wall thicknesses desired and the low wall thermal resistance associated therewith, since the temperature balance is impaired by heat conduction in the wall at small wall thicknesses. Furthermore, due to the deflection of the cooling fluid, which automatically occurs, an impulse can be applied, and this impulse is advantageous for the cooling effect of the cooling film, as has been described, for example, in Patent U.S. Pat. No. 4,384,823. A swirl can also be produced in the “prechamber” of the film-cooling hole, as described in Patent U.S. Pat. No. 4,669,957.




A first preferred embodiment of the blade according to the invention is distinguished by the fact that turbulence-generating elements are arranged in the internal cooling passages. In this way, the contact between cooling fluid and passage wall and thus the internal cooling can be further improved.




Specific amounts of cooling can be achieved if, as in a second preferred embodiment of the invention, cavities are arranged in the internal cooling passages for setting the cooling-fluid pressure or the cooling-fluid mass flow.




The internal cooling can also be improved if, as in another preferred embodiment, first ribs are arranged in the internal cooling passages for enlarging the heat-transfer area. First ribs can be designed so as to alternate in the flow direction as outer ribs and inner ribs, with the inner ribs having a larger height and/or width than the outer ribs.




A further increase in the cooling effect in the interior of the blade is achieved if, as in a further preferred embodiment of the invention, first impingement-cooling holes are provided in order to supply the internal cooling passages. The cooling fluid is passed through the impingement-cooling holes and enters the internal cooling passages in the form of impingement jets.




In addition to the internal cooling passages, a cooling passage may also be arranged in the blade nose. Cooling fluid is admitted into this cooling passage through second impingement-cooling holes. Second film-cooling holes are preferably directed from the cooling passage to the blade surface, the second impingement-cooling holes and the second film-cooling holes are arranged alternately, and second ribs are arranged between the second impingement-cooling holes and the second film-cooling holes for increasing the heat-transfer area and for separating the zones of the cooling passage which belong to the second impingement-cooling holes and the second film-cooling holes.




The internal cooling passages may run axially, and the film-cooling holes may in each case branch off from an associated internal cooling passage at an angle in the radial direction. However, it is also conceivable for the internal cooling passages to run axially, for the ends of the internal cooling passages to be connected by radial passages, and for the film-cooling holes to in each case be arranged between the internal cooling passages and start from the radial passages. Furthermore, it is conceivable in this connection for the internal cooling passages to run at an angle in the radial direction, and for the film-cooling holes to in each case branch off from an associated internal cooling passage in the axial direction. Alternatively, the internal cooling passages can run at a first angle in the radial direction, and the film-cooling holes can in each case branch off from an associated internal cooling passage at a second angle in the radial direction. In all cases, the film-discharge surfaces are arranged so as to be offset from the convective internal cooling passages, so that the internal cooling takes place precisely where the film cooling is less effective.











BRIEF DESCRIPTION OF THE DRAWINGS




The invention is explained in more detail below with reference to exemplary embodiments in connection with the drawings, in which:





FIG. 1

shows, in a cross section of the marginal region of a blade according to the invention, a first preferred exemplary embodiment for an individual internal cooling passage with cooling fluid directed in counterflow to the hot-gas flow, and with additional turbulence-generating means provided in a portion of the internal cooling passage;





FIG. 2

shows an exemplary embodiment comparable with

FIG. 1

having cavities in the internal cooling passages for setting the cooling-fluid mass flow;





FIG. 3

shows an exemplary embodiment comparable with

FIG. 1

having additional ribs in the internal cooling passage for enlarging the heat-transfer area;





FIG. 4

shows, in a cross section, the leading-edge region of a cooled blade in another exemplary embodiment of the invention having an additional cooling passage in the blade nose;





FIG. 5

shows, in an enlarged detail from

FIG. 4

, the blade nose with additional subdividing ribs in the cooling passage close to the edge;





FIGS. 6-9

show various exemplary embodiments for the (offset) arrangement according to the invention of internal cooling passages and film-cooling holes in the radial direction of the blade according to the invention;





FIGS. 10A and 10B

show two preferred exemplary embodiments for the arrangement of a plurality of film-cooling holes for each internal cooling passage in a blade according to the invention;





FIG. 11

shows an exemplary embodiment of the blade according to the invention having a deflection of the fluid flow into the counterflow by specific directing of the internal cooling passages; and





FIG. 12

shows another exemplary embodiment of the blade according to the invention having a deflection of the fluid flow by the positioning of the feeds (impingement-cooling holes) for the cooling fluid to the internal cooling passages.











DESCRIPTION OF THE PREFERRED EMBODIMENTS




A first preferred embodiment of the invention, as shown in

FIG. 1

, includes an individual internal cooling passage having cooling fluid directed in counterflow to the hot-gas flow. Portions of the cooling passage are provided with and without additional turbulence-generating means, as shown in

FIG. 1

in a cross section of the marginal region. The blade


10


is exposed along blade surface


11


to a hot-gas flow


18


(long arrow pointing from right to left). Internal cooling passages


14


are arranged below the blade surface


11


, and are separated from the blade surface


11


only by a thin wall


12


of thickness D and run parallel to the blade surface


11


. A cooling fluid, preferably cooling air—is fed at one end to the internal cooling passages


14


, preferably via impingement-cooling holes


13


. The cooling fluid then passes through the internal cooling passages


14


in counterflow to the (external) hot-gas flow


18


. It is deflected in a deflection space


15


located at the other end of the internal cooling passages


14


and leaves the blade


10


as a film flow


17


through film-cooling holes


16


, which start from the deflection space


15


in the direction of the hot-gas flow


18


, in order to form a cooling film on the blade surface


11


. In this case, the internal cooling passages


14


may have smooth walls; but may also be provided with turbulence-generating elements


19


,


19


′, as can be seen on the right in FIG.


1


.




This type of cooling is based on the idea of directing the cooling fluid first of all in counterflow to the hot-gas flow


18


in convective passages located close to the wall, which are integrated in the overall structure and can be provided with turbulence-generating devices, before the cooling fluid is used for the film cooling. As a result, very uniform temperature distributions are produced, which is very important for the small wall thicknesses D desired and the low wall thermal resistance associated therewith, since the temperature balance is impaired by heat conduction in the wall


12


at small wall thicknesses. Furthermore, due to the deflection of the cooling fluid, which automatically occurs, an impulse can be applied, and this impulse is advantageous for the cooling effect of the cooling film forming on the surface.




Furthermore, as shown in

FIG. 2

, the connectively cooled internal cooling passages


14


may be provided with larger cavities


21


, which enable the fluid pressure to be set in order to improve the film-cooling effectiveness and set the desired cooling-fluid mass flow.





FIG. 3

shows a further variant, by means of which the fluid pressure can be set and the surface necessary for the heat dissipation can be enlarged and the turbulence and thus the heat transfer can be increased. In this case, the integral convective internal cooling passages


14


are directed serpentine-like around inner and outer ribs


23


and


22


respectively. The internal cooling passage is again fed with cooling fluid by one (or more) impingement cooling hole(s)


13


. The cooling fluid is then passed as a cooling film (through film cooling holes


16


which are angled in the flow direction and/or in the lateral direction and may be provided with diffuser extensions) in counterflow onto the outer blade surface


11


. To account for the different temperature conditions, the inner ribs


23


should preferably be larger in height and/or width than the outer ribs


22


.




Especially effective cooling can be achieved with the cooling geometry illustrated in

FIG. 4

at the leading-edge region of a gas-turbine blade, in which case a combination with an impingement-cooled (and possibly film-cooled) blade nose


43


, as described in Patent EP-Al-0 892 151, is possible. The walls of the blade


40


are provided with a plurality of the cooling arrangements


44


-


46


already described above, which in each case comprise internal bores


14


that are supplied with cooling fluid in counterflow on the inlet side from a (radial) main passage


50


via impingement-cooling holes


13


. The cooling fluid is discharged as a cooling film on the outlet side via deflection spaces


15


and film-cooling holes


16


onto the blade surface (pressure surface


41


or suction surface


42


). A cooling passage


47


is provided for cooling in the blade nose


43


, and is supplied from the main passage


50


through impingement-cooling holes


49


. The cooling film is delivered to the outside surface of the blade nose


43


via film cooling holes


48


.




As shown in

FIG. 5

, effective cooling may be further improved with the outer ribs


51


described above. These ribs


51


, which may also be interrupted in the radial direction and then constitute rib segments (or pins), increase the heat-dissipating surface. Ribs


51


separate the surfaces that are struck by the impingement jets from the impingement-cooling holes


49


from the cavities from which the film-cooling holes


48


start. In this case, the film-cooling holes


48


may be arranged at an angle in the radial direction (perpendicular to the drawing plane of FIG.


5


). This achieves the effect that the cooling fluid sweeps over the entire heat-dissipating surface available and high cooling effectiveness is achieved.




The arrangements specified permit a homogeneous material temperature distribution in the flow direction of the hot-gas flow


18


, i.e. in the axial direction of the gas turbine. However, the invention also achieves a homogeneous distribution in the radial direction (perpendicular to the drawing plane in

FIGS. 1

to


5


) in order to increase the service life of a gas-turbine blade. This is ensured by the special arrangement according to the invention of internal cooling passages and film-cooling holes. The film-discharge surfaces (discharge openings of the film-cooling holes) are arranged so as to be offset from the convective internal cooling passages. Since the cooling effect of the film cooling between the holes is less than in the axial direction downstream of the holes, the cooling effect of the internal cooling can be utilized in these intermediate regions.





FIGS. 6-9

show possible basic arrangements which follow this idea. In

FIG. 6

, a plurality of internal cooling bores


141


-


143


are arranged in the radial direction


52


of the blade one above the other and parallel to one another at a uniform distance apart in the axial direction (parallel to the hot-gas flow


18


). Film-cooling holes


161


-


163


are directed from the outlet-side ends of the internal-cooling passages


141


-


143


to the blade surface, which lies in the drawing plane. The film-cooling holes


161


-


163


are made at an angle in the radial direction, so that their (oval) film-discharge openings are in each case arranged between the internal cooling passages


141


-


143


lying in the wall.





FIG. 7

illustrates an arrangement in which the ends of internal cooling passages


141


-


143


running axially in the wall are connected by radial passages


24


. The film-cooling holes


161


-


163


are made between the internal cooling passages


141


-


143


so as to start from the radial passages


24


and run parallel to the internal cooling passages


141


-


143


.





FIG. 8

shows a further arrangement. The internal cooling passages


141


-


143


are in this case made in the blade wall at an angle in the radial direction, whereas the film-cooling holes


161


-


163


branching off from them run axially. Combinations of these arrangements can be provided, as shown in

FIG. 9

for example. In this case, both the internal cooling passages


141


-


143


and the film-cooling holes


161


-


163


are made at an associated angle in the radial direction. The matrix structure produced is especially effective for homogenization of the material temperature in the radial direction. In all cases, a plurality of film-cooling holes


161


-


161


″ and


162


-


162


″ for each internal cooling passage


141


and


142


respectively, can be provided as shown in

FIG. 10A

for angled passages and axial holes, and as shown in

FIG. 10B

for angled passages and angled holes. This is of course also possible for the other arrangements described.




The counterflow principle according to the invention for the homogenization of the wall temperature in the axial and radial directions may also be realized by the convective internal cooling passages


141


-


143


themselves, as indicated in

FIGS. 11 and 12

. In these cases, for the internal cooling air, the counterflow is achieved either by deflections


53


,


54


(

FIG. 11

) or by feeding and discharging the cooling medium (e.g. via impingement-cooling holes and the film-cooling holes, as described above) at different axial positions (FIG.


12


).



Claims
  • 1. A cooled blade for a gas turbine, comprising:a wall; internal cooling passages located close to the wall and separated from a blade surface by the wall, at least some of said internal cooling passages being positioned for directing the flow of a cooling fluid, preferably cooling air for convective cooling, in counterflow to hot-gas flow flowing around the blade during operation of the gas turbine; and first film-cooling holes leading from said internal cooling passages to the blade surface, a plurality of said internal cooling passages and said first film-cooling holes being arranged one above the other in a radial direction of the blade with discharge openings of the first film-cooling holes being offset from the internal cooling passages and lying between the internal cooling passages.
  • 2. The blade as claimed in claim 1, wherein turbulence-generating elements are arranged in the internal cooling passages.
  • 3. The blade as claimed in claim 1, wherein cavities are defined in the internal cooling passages for setting the cooling-fluid pressure or the cooling-fluid mass flow.
  • 4. The blade as claimed in claim 1, wherein first ribs are arranged in the internal cooling passages for enlarging a heat-transfer area.
  • 5. The blade as claimed in claim 4, wherein the first ribs are arranged within the internal cooling passages to alternate in the flow direction as outer ribs and inner ribs, and the inner ribs have at least one of a larger height and a larger width than the outer ribs.
  • 6. The blade as claimed in claim 1, wherein first impingement-cooling holes are provided in connection with said internal cooling passages for directing cooling fluid into the internal cooling passages in the form of impingement jets.
  • 7. The blade as claimed in claim 1, wherein the first film-cooling holes are positioned for directing cooling fluid in the direction of the hot-gas flow before discharge from the first film-cooling holes.
  • 8. The blade as claimed in claim 1, wherein an additional cooling passage is provided in a nose of the blade, and second impingement-cooling holes are provided in connection with said additional cooling passage for directing cooling fluid into the additional cooling passage.
  • 9. The blade as claimed in claim 8, wherein second film-cooling holes lead from the additional cooling passage to the blade surface, said second impingement-cooling holes being arranged alternately with said second film-cooling holes; andsecond ribs or rib segments being arranged between the second impingement-cooling holes and the second film-cooling holes for increasing the heat-transfer area and for separating zones of the additional cooling passage associated with the second impingement-cooling holes and zones associated with the second film-cooling holes.
  • 10. The blade as claimed in claim 1, wherein the internal cooling passages run in an axial direction of the blade, and the film-cooling holes each branch off from an associated internal cooling passage at an angle in the radial direction of the blade.
  • 11. The blade as claimed in claim 1, wherein the internal cooling passages run in an axial direction of the blade, with ends of the internal cooling passages being connected by radial passages, and the film-cooling holes being arranged between the internal cooling passages and starting from the radial passages.
  • 12. The blade as claimed in claim 1, wherein the internal cooling passages run at an angle in the radial direction, and the film-cooling holes each branch off from an associated internal cooling passage in the axial direction.
  • 13. The blade as claimed in claim 1, wherein the internal cooling passages run at a first angle in the radial direction, and the film-cooling holes each branch off from an associated internal cooling passage at a second angle in the radial direction.
  • 14. The blade as claimed in claim 1, wherein a plurality of film-cooling holes branch off from an internal cooling passage distributed over the passage length.
  • 15. The blade as claimed in claim 1, wherein deflections are provided in the internal cooling passages for producing the counterflow.
  • 16. The blade as claimed in claim 1, wherein the internal cooling passages are adapted to receive a cooling fluid at different axial positions for producing the counterflow.
Priority Claims (1)
Number Date Country Kind
100 01 109 Jan 2000 DE
Parent Case Info

This application claims priority under 35 U.S.C. §§ 119 and/or 365 to Appln. Ser. No. 100 01 109.8 filed in Germany on Jan. 13, 2000; the entire content of which is hereby incorporated by reference.

US Referenced Citations (16)
Number Name Date Kind
4384823 Graham et al. May 1983 A
4669957 Phillips et al. Jun 1987 A
4770608 Anderson et al. Sep 1988 A
5370499 Lee Dec 1994 A
5383766 Przirembel et al. Jan 1995 A
5419039 Auxier et al. May 1995 A
5419681 Lee May 1995 A
5562409 Livsey et al. Oct 1996 A
5651662 Lee et al. Jul 1997 A
5667359 Huber et al. Sep 1997 A
5702232 Moore Dec 1997 A
5720431 Sellers et al. Feb 1998 A
5752801 Kennedy May 1998 A
5931638 Krause et al. Aug 1999 A
6247896 Auxier et al. Jun 2001 B1
6254334 LaFleur Jul 2001 B1
Foreign Referenced Citations (3)
Number Date Country
2 061 729 Jun 1971 DE
0 742 347 Nov 1996 EP
9906672 Feb 1999 WO