Thermally stressed turbomachine vane with a ceramic insert in the leading edge

Technical field

p0001The present invention relates to a thermally loaded blade for a turbomachine.

State of the art

p0002The demand for high efficiency in a turbine takes only a high pressure ratio to higher turbine inlet temperatures. Currently available blade materials for such turbines tolerate these temperatures but only in accordance with good cooling. The necessary cooling air is diverted from the combustion air stream and hence does not participate in the energy supply in the combustion chamber, which leads to a reduction in the efficiency of the power plant.

p0003In order to save cooling air, currently many attempts are made to protect the turbine blades with a ceramic coating, or even produce the entire blade of a ceramic material. With ceramic coating generally is a danger of bursting of the structure, especially when necessary to work with thicker layers, 0.5-1.5 mm. Become thinner ceramic layers provided in contrast, they must be cooled by a cooling air film, which contradicts the actual task of a thermal barrier coating. Big-ceramic blades are not currently able to withstand the forces and stresses occurring over a sufficiently long operating time.

Summary of the Invention

p0004The invention aims to remedy this. The invention, as characterized in the claims, the task is to propose measures at a blade of the aforementioned type, which provide the blades without blowing out cooling air a sufficiently large thermal protection.

p0005According to the invention the leading edge of the blades is provided from a ceramic material while the remainder of the blade may be auszulegt in a conventional manner. This has the following advantages:<ul><li>a) The leading edge of each turbine blade is of lower geometric dimensions. Accordingly, one has to do with small ceramic components that are very problematic in itself, with regard to the above-mentioned ceramic problems;</li><li>b) the forces of the blades and the blades are added to the same conventional type of metal part; the ceramic carries only the load from the temperature gradient, and to a lesser extent from occurring aerodynamic forces;</li><li>c) the leading edge of the blade can be constructed suitable for ceramics, ie generous curves, uniform wall thicknesses, favorable temperature gradient, sufficiently large contact surface are provided.</li></ul>

p0006The effects thereof are a considerable improvement in efficiency, especially at the first Turbinenleitreihen, an improvement of aerodynamics, as well as a considerable saving in cooling air.

p0007Advantageous and expedient further developments of the inventive task solution are defined in the further claims.

p0008All elements which are required for direct understanding of the invention have been omitted. Identical elements are provided in the various figures with the same reference numerals.

Brief Description of the Figures

p0009It shows:<dl id="dl0001"><dt>Fig. 1</dt><dd>a turbine blade with a ceramic leading edge,</dd><dt>FIG. 2</dt><dd>the ceramic front edge portion of the turbine blade, according to FIG. 1,</dd><dt>Fig. 3</dt><dd>a three-dimensional view of a ceramic front edge,</dd><dt>Fig. 4</dt><dd>a view of the divisions within the ceramic leading edge,</dd><dt>Fig. 5</dt><dd>an attachment of the ceramic leading edge and</dd><dt>Fig. 6</dt><dd>another fixing the ceramic front edge.</dd></dl>

WAYS OF IMPLEMENTING THE INVENTION, COMMERCIAL APPLICABILITY

p0010Fig. 1 shows a turbine blade 1 as it is normally used in gas turbines. This has inwardly relatively large cooling ducts through which a cooling medium flows. Obviously, a first cooling air passage 10 for the front edge portion 2, and a further cooling air passage 11 for the rear section of the blade are 1. The leading edge section 2 of this consisting of a high-quality metal blade 1 is drawn to accommodate the Applizierung one consisting of a high-quality ceramic material cupped front edge 3, hereafter called ceramic front edge to create. Preferably blade 1 and ceramic front edge 3 over means are interconnected, which are able to create a force fit and / or positive connection between the two in the coupled state. For this purpose, the head stage 4 of the blade 1 in the present case both the suction and pressure side each have a notch 5a, 5b, which permits the mechanical imposition of the ceramic front edge 3 to the metallic head stage 4 of the blade first The traction required for anchoring is created on one side, for example in the notch 5a, with at least one spring element 6, the latter being preferably of cylindrical configuration. The ceramic front edge 3 is first mounted along the notches 5a, 5b, and then anchored to the radial insertion of the spring element. 6 The ceramic front edge 3 is thus on two lines, and is free to move against the spring element 6 thermally within a certain degree of freedom. A gap 7 between head stage 4 and inside of the ceramic front edge 3 serves as insulation, since a bubble is present, which is additionally cooled by the leakage of the said lines. The gap 7 is powered by a kind of "Showerheadkühlung" (= cooling by several rows), the air flow rate is limited by the linear bearing surface on a very small amount. Basically, the head stage 4 of the blade 1 is configured such that a, if not optimal, yet sufficient aerodynamics is guaranteed. Furthermore, this head step 4 is cooled via a number of cooling air holes 8 so that an operating without a ceramic leading edge 3 is possible over a limited period of time without difficulty. The ceramic front edge 3 has a wall thickness of typically 3-8 mm. Both the front edge portion 2 and the remaining part of the blade 1 are provided with cooling air holes 12, which are fed from the cooling air passages 10 and 11 and which effect a cooling film on the blade surface. Danebst are 4 more cooling holes 9 are mounted in the region facing away from the head level, which trigger a cooling film between metal and ceramic portion of the blade 1, thus also this delicate game is optimally cooled terms of acting there coupling between the two parts. In addition to conventional ceramics, the use of advanced fiber-reinforced ceramic is possible, which, far better is immune against harmful effects, especially mechanical. The cup-shaped configuration of the ceramic front edge 3 is the training counter with a fiber-reinforced ceramic. To better understand the leading edge section 2 of the blade 1 in FIG. 2 is taken up again on a larger scale, and, if necessary, be further described.

p0011Fig. 2 shows the front edge portion 2 of the blade 1, as has already been described largely with reference to FIG. 1. From this figure, the structure of the suspended ceramic front edge 3 as well as the intended means 6 goes resp. 5a, 5b significantly to produce the coupling and a frictional connection and / or positive connection between the two parts 3/4 out.

p0012Fig. 3 shows a three-dimensional view of the ceramic leading edge already described with Fig. 1 and 2, which here because of their special training, Pos. 20 carries. If occurring in this ceramic front edge 20 radial stresses when installed should be too large, can help here to be created by the ceramic leading edge 20 twice in the radial direction or is divided into three parts, in which case, special steps must be provided when mounting mechanism for the various parts.

p0013From FIG. 4, the division of such a ceramic leading edge 20 is evident. The parting line 13 for this purpose are inclined to enlarge on the one hand, the sealing length, and in another case a direct flow of hot gases through the joints 13 within the ceramic leading edge 20 to prevent the arranged underneath the head stage of the blade. The joints can also extend perpendicular to simplify the manufacturing. In principle, the parting line can be designed.

p0014Fig. 5 shows a further variant of the device to attach the ceramic leading edge 3a. The head stage 4a here corresponds largely to that of FIG. 2. With regard to the device to attach the ceramic front edge 3a, so has this head stage 4a on both sides relatively large notch 16a, 16b. In the area of ​​these notches 14 are slits on both sides of the head stage 4a example eroded, thus capable suspension tongues 15, short spring tongues called, occur which create the force fit between the two parts to be joined. Since a proportionate strong spring action must be provided to compensate for different thermal expansions, the installation direction of the ceramic front edge 3a is provided radially as the here available travel is not sufficient to push the ceramic front edge 3a from the front over the spring tongues 15th In order to provide the desired spring action, but only a very small spring travel is necessary, especially since this is divided into two pages.

p0015Fig. 6 shows a massive provided with a dovetail root ceramic front edge 3b, which is also installed radially. The head stage 4b of the blade has delivered an open cut leading edge, the one whose profile is a dovetail root. Off course other profiles are also possible for this purpose. The ceramic front edge 3b is pressed on the root against the head stage 4b by way of resilient metal insert 17, which is embedded in the front cooling pin 10. The air flowing through this duct 10 cooling air is passed through appropriate openings 18 by the metal insert 17 and flows finally along cast into the head stage 4b grooves 19, which 3b connected to the internal shape of the ceramic leading edge, further, whereby a sufficiently large cooling surface of the ceramic part at the metal member is ensured. The resilient metal insert 17 is designed so that it is likely in the absence of ceramic front edge 3b on the plane formed by the head stage 4b opening, such that a sufficient aerodynamics is guaranteed in this area. Also guaranteed is the cooling of the head stage 4b which passes through the said openings 18 vonstatten.

p0016All proposed solutions, the pressure difference of the cooling air flowing over the hot gas here helps to press defines the respective ceramic front edge. The solutions also exhibit suitable for ceramics configuration as largely present on the one hand by the present temperature in the steady state only compressive stresses on the ceramic front edge. In the solutions that make use of a voltage generated by springs, care must be taken that in the transient load ranges, the minimum required for this spring force is not lost, and that no damaging tensile stresses occur on the ceramic materials. Preferably, the suspension is always provided where a sufficient cooling of the spring elements is ensured. Basically similar solutions by attaching ceramic parts for the trailing edge of the blade, who are also high thermal stresses.

LIST OF REFERENCE NUMBERS

p0017<dl id="dl0002" compact="compact"><dt>1</dt><dd>shovel</dd><dt>2</dt><dd>Front edge portion</dd><dt>3</dt><dd>Ceramic front edge</dd><dt>3a</dt><dd>Ceramic front edge</dd><dt>3b</dt><dd>Ceramic front edge</dd><dt>4</dt><dd>head level</dd><dt>4a</dt><dd>head level</dd><dt>4b</dt><dd>head level</dd><dt>5a</dt><dd>notch</dd><dt>5b</dt><dd>notch</dd><dt>6</dt><dd>spring element</dd><dt>7</dt><dd>Gap, air gap</dd><dt>8th</dt><dd>Cooling air holes</dd><dt>9</dt><dd>Cooling air holes</dd><dt>10</dt><dd>Front cooling air duct</dd><dt>11</dt><dd>Rear cooling air duct</dd><dt>12</dt><dd>Kühllluftbohrungen</dd><dt>13</dt><dd>parting line</dd><dt>14</dt><dd>slots</dd><dt>15</dt><dd>spring tongues</dd><dt>16</dt><dd>contact surfaces</dd><dt>17</dt><dd>A resilient metal insert</dd><dt>18</dt><dd>Cooling air openings</dd><dt>19</dt><dd>Kühlluftnuten</dd><dt>20</dt><dd>Divided ceramic front edge</dd></dl>