Turbine blade with actively cooled head platform

TECHNICAL FIELD

The present invention relates to the field of gas turbines. It concerns an air-cooled turbine blade which a perpendicular to the blade tip to the blade longitudinal axis extending shroud element, wherein the shroud element for the purpose of cooling a plurality of cooling holes is traversed, which on the input side with at least one through Turbine blade extending to the blade tip cooling air duct connected standing and on the output side into the outer space surrounding the turbine blade open.

Generic type turbine blades are known from DE 198 13 173 A1 or from US 5,785,496 known.

STATE OF THE ART

Modern gas turbines operate at extremely high temperatures. this requires an intensive cooling of the turbine blades. A particular difficulty is is to cool the exposed areas of the blades reliably. one these ranges are the shroud and the shroud elements of the blade. One possibility for the cooling of shroud elements in the above-mentioned Document DE 198 13 173 A1 described. It is proposed (See the local Fig. 3 and 4), the shroud elements by a series cool parallel cooling bores, which extend from the (central) blade through the shroud element to the outer edge of the shroud-band element towards extending and open there in the outer space.

However, this known solution has the following disadvantages:<ul><li>Poking two shroud elements of adjacent blades laterally to each other (As for example from Fig. 3 of US 5,482,435 can be seen), the mouths are the cooling holes at least partially closed. This hinders Cooling air outlet and distribution. The shroud element is overheated during operation.</li><li>The known cooling shroud changes because of the laterally arranged openings not Überströmbedingungen over the shroud, which means, Pressure and temperature on the top of the cover tape will remain the same. This is not changed thereby, that- as in the US 5,460,486 proposed - Certain cooling holes on the underside of the shroud-band element open.</li><li>The cooling effect is mainly due to the mixing of the exiting through Cooling air with the hot gas mixing temperature lowered in the shroud Surroundings. Shall be taken in the cooling holes and no measures, to the heat transfer between the cooling air and the shroud element to intensify.</li></ul>

SUMMARY OF THE INVENTION

It is therefore an object of the invention, a turbine blade with air-cooled to provide shroud element in which the mentioned disadvantages in a simple Way be avoided, and, through an effective cooling of the shroud element in particular also on the exposed upper surface of the shroud-band element, distinguished.

The object is solved by the totality of the features of claim 1. Advantageous embodiments provide the dependent claims again.

The basic idea of ​​the invention, the cooling holes for a so to carry out the shroud element that a high heat transfer between Shroud element and cooling air is ensured and on the other hand these bores so to allow flow into the outer space, the exposed regions of the Shroud be reliably supplied with the cooling air and additionally cooled. This is accomplished by subtracting from the cooling passage of the blade, starting in the area of Shroud element the cooling holes substantially parallel to the direction of movement extend the blade tip from the inside out, and each of outer edge of the shroud element in a room to the outside open towards recess the surface flow.

In a first preferred embodiment of the invention are in the Shroud element embedded recesses close to the outer edge of the upper side, in which the cooling holes open laterally. By mixing the exiting cooling air with the hot combustion gases, which flow over the top of the shroud-band element, the temperature effectively reduced in this area and so overheating of the shroud avoided. This provides a uniform cooling of the shroud element achieved over the entire surface. In addition to an effective cooling of the shroud top has this configuration also has the advantage of a very simple preparation. Particularly effective is the outlet of the cooling air on the top side of the shroud-band element, if, according to a preferred development on top of the The shroud element mutually parallel, spaced-apart Sealing ribs are provided which in interaction with the opposite Housing wall of the gas turbine form a cavity and the cooling holes open into this cavity. The exiting cooling air leads to a pressure build-up in the cavity, in consequence of the penetration of hot gases is diminished.

According to another embodiment of the invention have the side edges of the Shroud elements recesses which open in the cooling holes. recesses opposite shroud elements thereby form a gap. Upon exit into the gap the cooling air is divided into two partial flows. A part flows toward the upper side and feeds the mentioned cavity between the spaced Sealing ribs with the above-mentioned effect. The remainder flows to Shroud bottom, where it mixes with the hot gases, setting a mixing temperature that reduces the thermal stress in this area. By gap geometry, the ratio of flowing up and down Subsets are affected.

In an expedient feature of the invention is also proposed in the cooling holes agents for improving the heat transfer between provide cooling air and shroud element. The agent for improving the heat transfer to the bore walls can Roughness, ribs and / or turbulators comprise. In per se known Example, the holes by means of the so-called "STEM drilling" process to be created. In particular, through the "STEM drilling", for example, in the US 5,306,401 in connection with the manufacture of cooling holes in turbine blades has been described, can be easily and reliably cooling bores produce with improved heat transfer characteristics.

A better utilization of the cooling air can also be achieved if, in accordance another preferred embodiment of the invention in the cooling holes each a restrictor to limit the cooling air mass flow is provided, and the throttle points respectively on the input side of the cooling holes are arranged.

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="5"><dt>Fig.1</dt><dd>Plan view of a preferred embodiment of the turbine blade with exiting the shroud upper side cooling holes</dd><dt>Fig.2</dt><dd>Another embodiment according to Fig.1 with diffuser-like cooling holes</dd><dt>Fig.3</dt><dd>Side view of a shroud element according to Figure 1 with cooling holes of circular cross-section</dd><dt>Fig.4</dt><dd>Side view of a shroud element according to Figure 1 with cooling holes of oval cross-section</dd><dt>Fig.5</dt><dd>Partial sectional view of a shroud element according to Fig.1</dd><dt>Fig.6</dt><dd>Top view of two shroud elements in one embodiment, with exiting to the side edge towards cooling holes</dd><dt>Figure 7</dt><dd>Partial sectional view of a shroud element according to Figure 6</dd><dt>Figure 8</dt><dd>Partial sectional view of a shroud element with cooling air outlet to the bottom of the shroud element towards</dd></dl>

WAYS OF IMPLEMENTING THE INVENTION

In Fig. 1 is a top view of a preferred embodiment of a turbine blade prepared according to the invention. The turbine blade 10 includes the actual Blade profile 23 and a transverse thereto is arranged on the blade tip Shroud element 11 which, together with the shroud elements of the other (Not shown) blades a continuous, mechanically stabilizing Shroud results. The blade profile 23 is inside partially hollow and of a or a plurality of cooling air ducts 18 passed through the cooling air from the blade root lead to the blade tip. The shroud member 11 has on its upper side 22, two parallel in the moving direction of the blade tip sealing ribs 12 and 13, which together with the opposite housing wall 20 of the gas turbine form a united through gaps with the surrounding cavity 21st extend inside the shroud member 11 between and substantially parallel to the ribs 12, 13 a plurality of cooling holes 17 from the center outward. The cooling holes 17 are provided on the input side with the cooling air duct 18 in connection and are supplied by this cooling air. As shown in FIG. refer 1, the cooling holes 17 do not extend completely to the side End or edge of the shroud element 11, but each open of the side into an oblong on the top surface 22 in the shroud element 11 recessed groove 14. It goes without saying that instead of a 14, each of the cooling holes 17 taken through depression itself with a separate recess may be in communication. Furthermore, it is also conceivable for the cooling holes 17 and slightly inclined from a parallel to each other to let run differently when to optimize cooling over the entire area of ​​the shroud-band element 11 is necessary.

Furthermore, a blow of the cooling air leads upwardly to an "inflation" of the Cavity 21 between the shroud and housing 20. This leads to an increase of the Pressure in the cavity and therefore contributes to a reduction of the invading Mass flow in to the hot gas 24th Furthermore, of course, is also the mix temperature is lowered in this area, whereby the thermal loading of the The shroud element 11 is reduced from the upper side 22 forth.

The cooling holes 17 in the cooling assembly shown are preferably with the so-called "STEM drilling" made process, which in the US 5,306,401 describes in great detail. Thereby, it is (by changing of the feed) are possible, the surface of the cooling bores 17 with asperities, equip ribs or turbulators. This leads to a much more efficient Cooling, because the shape of the coolant hole can be optimized. furthermore it is advantageous for the cooling holes 17, preferably on the input side, ie in the region the cooling air supply to the profile 23, to equip each with a restrictor 19th This makes it possible to limit the cooling air mass flow targeted and to obtain a much more efficient cooling. The embodiment shown in Figure 2 differs from that according to Figure 1 in that the cooling holes 17 from the throttle point 19, which at each of Input side of each cooling bore arranged as a diffuser or diffuser similar are formed. According to a further embodiment - illustrated in Figure 4 -, the cooling holes an oval configuration. This increases, as the equipment with internal Roughness or the diffuser-like enlargement, the heat transfer Available surface area. The cooling holes 17 may additionally or alternatively other configurations than the described above. As such, for example, regularly or irregularly held depressions or corrugations conceivable.

contact In a further favorable embodiment of the invention according to FIG. 6 and 7 the cooling holes 17 on the side edge 25 of the shroud member 11 from. are the side edges to avoid the disadvantages of the prior art 25 the shroud elements 11 but carried out so that adjacent elements 11 only regions are in contact, the area of ​​the exiting cooling holes but is in contrast withdrawn in a recess 15th Between adjacent elements form the opposing indentations 15 column 26, in which the cooling air enters. This embodiment reliably prevents closing the mouths of adjacent shroud elements. It ensures that the cooling air always the cooling holes 17 may pass, even if two adjacent shroud elements 11 are in mechanical contact. The entering of two adjacent elements 11 in the gap 26 cooling air is divided into two partial flows. A partial stream flows upwards and leads to a Inflating the cavity 21 above the shroud, while the other part stream reaches the bottom of the shroud and there with the hot gases mixed. The mixtemperature reduces the thermal load in this area. The structural design of the gap, the proportion of two partial flows are affected. Thus, top and bottom of a different having gap width or the boundary walls or inclined be designed aerodynamically different.

8 shows an embodiment with a coolant outlet on the underside of Shroud element. The cooling holes 17 open laterally into the recess 16th According to this variant, the mixing temperature in the region of the underside is the Shroud lowered, thereby reducing the thermal stress.

LIST OF REFERENCE NUMBERS

<dl tsize="8" compact="compact"><dt>10</dt><dd>turbine blade</dd><dt>11</dt><dd>Shroud element</dd><dt>12,13</dt><dd>sealing ribs</dd><dt>14,15,16</dt><dd>deepening</dd><dt>17</dt><dd>Kühlbohrunq</dd><dt>18</dt><dd>Cooling air duct</dd><dt>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</dt><dd>Outer edge of the shroud element</dd><dt>26</dt><dd>Gap between the shroud elements</dd></dl>