Turbine blade with air cooled tip shroud

TECHNICAL FIELD

The present invention relates to the field of gas turbines. It concerns an air-cooled turbine blade according to the preamble of claim 1.

Such turbine blade is known eg from US-A-5,482,435 or known the US-A-5,785,496.

STATE OF THE ART

Modern gas turbines operate at extremely high temperatures. This requires a intensive cooling of the turbine blades, which nowadays in modern gas turbines, be used. It is usually very difficult, the exposed Areas of the blades to cool well. One of these areas is the shroud or shroud element of the blade. One way to the shroud element to cool, is described in the aforementioned US-A-5,785,496 been. There is proposed (see the local Fig. 1A and 1B), the shroud element to be cooled by a series of parallel cooling bores of itself the (central) blade through the shroud element through the outer Edge of the shroud element extend and open there in the outer space. In US-A-5,482,435 for the same purpose are only two in opposite Directions ongoing drilling provided.

However, these known solutions have disadvantages: The known cooling holes take within the shroud element comparatively little space on. As for the introduction of the holes in the shroud element a certain minimum thickness of the shroud-band element is needed, and this or even more Thickness of the shroud-band element also in the region outside of the holes is maintained, an unfavorable ratio of small perfused results Shroud volume to no flow through the shroud volume. As a consequence, that the cooling of the shroud element is not optimal, and in that the shroud element due to the large proportion of solid material comparatively is difficult and thus high during operation due to the centrifugal forces mechanical stress is exposed.

To solve this problem it has been proposed (GB-A-2,290,833), practically running in the interior of the shroud element cooling holes to refrain entirely and instead of cooling air in the manner of a film cooling of a Distributing channel over a series of small openings on the top of to leave the shroud element flow out to a thinner and lighter Shroud element to allow. The problem, however, is that the effectiveness This surface film cooling of the shroud element greatly from the on the top of the shroud element prevailing flow conditions dependent and therefore difficult to optimize for the various operating states can be.

SUMMARY OF THE INVENTION

It is therefore an object of the invention, a turbine blade with air-cooled Shroud element to provide; in which the mentioned disadvantages in a simple Way can be avoided, and in particular at significantly lighter of the shroud element by an effective cooling of the The shroud element is distinguished.

The object is solved by the totality of the features of claim 1. Essence of the invention is that the cooling fluid inside the cavities in the leading Shroud-band element in coordination with the shroud element in shape and dimension be designed so that the flow-through from the cooling fluid volume one high share of total of the shroud element occupies. hereby can with a very efficient cooling, the weight of the shroud element be considerably reduced.

A first preferred embodiment of the inventive turbine blade or vane is characterized in that the cavities comprise cooling holes, that the cooling bores are formed tunnel-shaped, the thickness of the The shroud element is reduced outside of the cooling bores, and that the Cooling bores substantially parallel to the direction of movement of the blade tip extend from the inside to the outside, and in front of the outer edge of the The shroud element open into the outer space upwards. The tunnel-shaped Training of the cooling holes does not only reduce the percentage of the solid material on Shroud element, but stiffened at the same time the shroud element mechanically. The escaping upward cooling air can then escape unhindered when the shroud elements of all blades of a turbine stage strung together to combined an annular shroud.

Preference is given thereto in the shroud element from the upper side indentations inserted, and opening the cooling holes laterally into the recesses. From It is also advantageous if the cooling holes each have a restrictor to limit of the cooling air mass flow is provided, and the throttle points respectively are arranged at the input side of the cooling holes. A part of Cooling holes may also be formed as a diffuser.

A second preferred embodiment of the invention is characterized in that the cavities are formed as slots which extend over the width of the shroud-band element extending in that the slits substantially parallel to the extend the movement direction of the blade tip from the inside out, and each before the outer edge of the shroud-band element upwards into the outer space open, in that the shroud element from the upper side indentations are embedded, and that the slots open into the recesses from the side. The wide slots give a good cooling combined with significant material reduction. Again, it may be advantageous in the slots respectively constrictions provide for limiting the cooling air mass flow, the throttle bodies respectively disposed at the input side and / or the output side of the slots are.

Particularly effective is the cooling, when, according to a preferred development in this embodiment the slots means to improve the heat transfer are provided between the cooling air and shroud element. Especially the slots as means for improving the heat transfer a include distributed array of pins, the turbulent flow around the cooling fluid and so the heat transfer between the cooling fluid and shroud material continue to improve.

A third preferred embodiment of the inventive turbine blade or vane distinguished by the fact that the cavities in the moving direction the blade tip extending cooling holes include that the cooling holes of a plurality are crossed by transverse bores, and that shut off the cross bores to the outer space through through closed ends are. This configuration of the intersecting cooling holes is on the geometry forth comparable to the aforementioned wide slots distributed pin arrangement. Again with strongly improved heat transfer is the solid material of the shroud element significantly reduced, thus saving weight. The intersecting cooling holes can be by conventional means comparatively easily bring to the shroud element. Cooling particular technical cheap cooling holes can be achieved if the cooling holes and the transverse holes made by the so-called "STEM drilling" process are.

Further embodiments result from the dependent claims.

BRIEF EXPLANATION OF THE FIGURES

The invention is below with reference to exemplary embodiments in conjunction be explained in more detail with the drawings. Show it<dl tsize="6"><dt>Fig. 1</dt><dd>in the top plan view of a first preferred embodiment according to the invention having the (dashed line of the turbine blade indicated) tunnel-shaped cooling holes in the shroud element;</dd><dt>FIG. 2</dt><dd>Seen from the side, the tip of the turbine blade according to Figure 1 within the gas turbine with the opposite housing wall.</dd><dt>Fig. 3</dt><dd>in a comparable to FIG. 1 through a second preferred Embodiment of the invention with wide slots and a regular array of pins in the slots; </dd><dt>Fig. 4</dt><dd>in a comparable to FIG. 2 illustration, the side view of the A blade according to Fig. 3;</dd><dt>Fig. 5</dt><dd>in a comparable to FIG. 1 depicting a third preferred Embodiment of the invention with intersecting cooling holes and cross-holes; and</dd><dt>Fig. 6</dt><dd>in a comparable to FIG. 2 illustration, the side view of the Blade in FIG. 5.</dd></dl>

WAYS OF IMPLEMENTING THE INVENTION

In FIG. 1 is in the top plan view of a first preferred embodiment the turbine blade shown according to the invention. The turbine blade 10 includes the actual (perpendicular to the plane extending) blade profile 23 and a transverse thereto which is arranged at the blade tip shroud element 11, which together with the shroud elements of the other (not shown) Blades a continuous, annular, mechanically stabilizing Shroud results. The blade profile 23 is inside partially hollow and of a or a plurality of cooling air ducts 18 (shown in phantom in Fig. 1 indicated) traversed, the cooling air from the blade root to the blade tip conduct (see, eg, Fig. 2 of US-A-5,482,435). The shroud member 11 has on its upper side (22 Fig. 2) two parallel in the moving direction of the blade tip ribs 12 and 13, which together with the opposite housing wall 20 of the gas turbine a connected by column around cavity 21 form (Fig. 2).

extend inside the shroud member 11 between and substantially parallel to the ribs 12, 13 a plurality of cooling holes 16, 16 'and 17, 17' (in FIG. 1 and 2 by dashed lines drawn in) from the center toward the outside. The Cooling bores can be of a uniform shape, but may also vary be configured. In the embodiment of Figs. 1 and 2, the Cooling holes 16, 17 as holes with substantially constant diameter designed during the cooling holes 16 ', 17' as diffusers in the flow direction widening cross-section are formed.

The cooling holes 16, 16 'and 17, 17' are provided on the input side with the cooling air duct 18 in connection with this and of cooling air (or other Cooling fluid) supplied. As can be seen from Fig. 1, the cooling bores extend 16, 17 is not quite up to the lateral end or edge of the shroud element 11, but in each case open from the side into an oblong, from Upper side let into the shroud element 11 recess 14 and 15 respectively. This ensures that the cooling air always passes through the cooling holes, although two (adjacent) shroud elements in mechanical Contact stand. It goes without saying that, instead of the continuous taken depressions 14, 15 also each of the cooling holes 16, 16 'and 17, 17' for itself with a separate recess may be in communication. It is further it is also conceivable that the cooling holes 16, 16 'and 17, 17' at a slight angle and from a with each other to let pass notwithstanding parallelism when optimizing the cooling over the entire area of ​​the shroud-band element 11 necessary is.

Furthermore, a blow of the cooling air leads upwardly to an "inflation" of the Cavity 21 in the shroud (Fig. 2). This leads to an increase in pressure in the Gap between shroud member 11 and housing wall 20 and thus contributes to a reduction of the invading mass flow of hot gas 24 at. furthermore is of course, the mixing temperature is lowered in this area, which the thermal load of the shroud member 11 from the top 22 is here reduced. Furthermore, it is advantageous for the cooling holes 16, 16 'and 17, 17 'preferably on the input side, ie in the region of the cooling air supply to the profile 23 to equip each with a restrictor 19th This makes it possible to to limit cooling air mass flow selectively and significantly more efficient cooling to obtain.

Critical to the inventive reduction of the weight of Shroud member 11 is in the embodiment of FIGS. 1 and 2, however, that the cooling holes 16, 16 'and 17, 17' are formed tunnel-shaped. The means that - is clearly seen in the side view of FIG. 2 - the Thickness of the shroud-band element 11 outside of the cooling holes 16, 16 '; 17, 17 ' is reduced. In this way, the shroud element considerable material and be thus saved weight. At the same time reduces to be cooled Material volume. Eventually form the tunnel-shaped cooling holes 16, 16 ' and 17, 17 'on top of the rib-shaped shroud element elevations, deemed essential to increase the mechanical rigidity of the shroud element 11 contribute.

An alternative form of weight reduction is in the embodiment of Fig. 3 and 4 are reproduced. Here 11 is the interior of the shroud-band element, instead a plurality of cooling holes on either side of the blade profile respectively a wide slot 25 and 26 respectively is provided, which in each case from the central cooling-air duct up to the lateral recesses 14 and 15, 18 extends and opens out there. The Slots 25, 26 lead due to their continuous width to a significant Weight reduction and ensure evenly over the entire width distributed cooling Again, each throttle bodies 19 or 19 'to limit of the cooling air mass flow can be provided, wherein the throttle points respectively on the input side (throttle points 19) and / or the output side (choke points 19 ') of the slits 25 are positioned 26th The cooling through the slots 25, 26 can be increased in their effect on, when the agent for improving of heat transfer in the slots a distributed arrangement (a "Array") of pins 27 is provided. Increase the pins 7 of the turbulence Cooling air flow and provide additional space is for the heat transfer. In addition, they act mechanically stabilizing when in the slots ranging from wall to wall. Number and arrangement of pins in the "array" can in Part of the optimization of the cooling effect can be changed.

A further alternative type of weight reduction in the present invention is in 5 and 6. FIG.. Here is the shroud element 11 is a "matrix" of parallel Cooling holes 16, 17 (drilling axis 29) and these intersecting cross holes 28 (drilling axis 30) generates, the terms in effect weight loss and cooling similar to the pin occupied slots of FIGS. 3 and 4 is. The cooling holes 16, 17 and the transverse holes 28 are - as well as the Cooling bores in Figures 1 and 2 -. Preferably the so-called "STEM drilling" process prepared which described in US-A-5,306,401 in detail is. Thereby, it is possible (by changing the feed rate), the Cooling holes 16, 17 and transverse bores 28 with internal roughness such as to provide turbulators or fins. This leads to a much more efficient Cooling, because the shape of the coolant hole can be optimized. The cooling holes 16, 17 and transverse bores 28 are sideways through after drilling closed ends 31 and 32 blocked. The cooling holes 16, 17 also preferably constrictions 19 and open into laterally arranged, upwardly open recesses 14, 15th

LIST OF REFERENCE NUMBERS

<dl tsize="13" compact="compact"><dt>10</dt><dd>turbine blade</dd><dt>11</dt><dd>Shroud element</dd><dt>12,13</dt><dd>rib</dd><dt>14,15</dt><dd>deepening</dd><dt>16,16 ', 17,17'</dt><dd>cooling hole</dd><dt>18</dt><dd>Cooling air duct</dd><dt>19.19 '</dt><dd>constriction</dd><dt>20</dt><dd>housing wall</dd><dt>21</dt><dd>cavity</dd><dt>22</dt><dd>Top (shroud element)</dd><dt>23</dt><dd>blade profile</dd><dt>24</dt><dd>hot gas</dd><dt>25,26</dt><dd>slot </dd><dt>27</dt><dd>Pin code</dd><dt>28</dt><dd>transverse bore</dd><dt>29,30</dt><dd>drilling axis</dd><dt>31,32</dt><dd>closed end</dd></dl>