Patent Application
20060002796
This application claims priority of European application No. 04015805.7 EP filed Jul. 5, 2004, which is incorporated by reference herein in their entirety.
The invention relates to a turbine blade for use in a gas turbine, with a blade leaf which is provided with a number of coolant ducts through which a coolant is capable of flowing, outlet ducts, which issue in outlet ports, branching off, in the leading edge region of the blade leaf, from a coolant duct running essentially in the longitudinal direction of the turbine blade and spaced apart from the leading edge.
Gas turbines are employed in many sectors for the drive of generators or of working machines. In this context, the energy content of a fuel is utilized in order to generate a rotational movement of the turbine shaft. For this purpose, the fuel is burnt in a combustion chamber, compressed air being supplied by an air compressor. The working medium, which is generated in the combustion chamber as a result of the combustion of the fuel and which is under high pressure and under a high temperature, is in this case routed via the turbine unit which follows the combustion chamber and where the working medium expands so as to perform work.
In this case, in order to generate the rotational movement of the turbine shaft, the latter has arranged on it a number of moving blades which are conventionally combined in blade groups or blade rows and which drive the turbine shaft via pulse transmission from the flow medium. Moreover, in order to route the flow medium in the turbine unit, guide vane rows connected to the turbine casing are usually arranged between adjacent moving blade rows. The turbine blades, in particular the guide vanes, in this case usually have, for the suitable routing of the working medium, a blade leaf which is extended along a blade axis and onto which a platform extending transversally with respect to the blade axis can be integrally formed on the end face for fastening the turbine blade to the respective carrier body. However, a platform or a platform-like configuration may also be attached to the other free end.
The design of gas turbines of this type is usually aimed at particularly high efficiency in addition to achievable power. In this case, for thermodynamic reasons, an increase in efficiency can be achieved, in principle, by an increase in the outlet temperature at which the working medium flows out of the combustion chamber and into the turbine unit. Temperatures of about 1200° C. to 1300° C. for turbines of this type are therefore sought after and even achieved.
At such high temperatures of the working medium, however, the components and structural parts exposed to this are exposed to high thermal loads. In order, nevertheless, to ensure a comparatively long useful life of the relevant components, along with high reliability, a cooling of the relevant components, in particular of moving blades and/or guide vanes of the turbine unit, is conventionally provided. The turbine blades are in this case conventionally designed to be coolable, in which case, in particular, an effective and reliable cooling of the leading edge of the respective turbine blade, said leading edge being subjected to particularly high thermal load, is to be ensured.
The coolant used is in this case usually cooling air. This is normally supplied to the respective turbine blade in the manner of open cooling via a number of coolant ducts integrated into the blade leaf or the blade profile. The cooling air, emanating from these coolant ducts, flows, in outlet ducts branching off from the latter, to the regions of the turbine blade which are in each case provided, with the result that a convective cooling of the blade interior and of the blade wall is achieved. These ducts are left open on the outlet side, so that the cooling air, after flowing through the turbine blade, emerges from the outlet ports, also designated as film cooling holes, and forms a cooling air film on the surface of the blade leaf. This cooling air film largely protects the material on the surface against direct and over intensive contact with the hot working medium flowing past at high velocity.
In order to make it possible to have particularly uniform and effective film cooling in the leading edge region of the blade leaf, the outlet ports are conventionally arranged there uniformly along at least two rows oriented parallel to the leading edge. Moreover, as a rule, the outlet ducts are oriented obliquely with respect to the longitudinal direction of the turbine blade, thus assisting the formation of the protective cooling air film flowing along the surface. Since, in the production of the turbine blade, the outlet ducts are normally introduced from outside at the conclusion for cost reasons, for example by laser drilling or other drilling methods, and particularly in the leading edge region of the blade leaf, access for the drilling instrument through the platform or platform-like configurations integrally formed on the end face is possibly obstructed, there is often, with regard to the oblique setting of the outlet ducts, a change in orientation at a transitional point lying approximately centrally between the root section and tip section of the respective blade leaf This takes place in that the coolant flowing out in a root-side subsection of each row possesses, in the region of the outlet ports, a velocity component which points toward the tip section, whereas cooling medium flowing out in a tip-side subsection, contiguous thereto, of each row has a velocity component pointing toward a root section. In other words: in the root-side subsection, the outlet ducts are inclined in the direction of extent to the turbine blade, whereas, in the tip-side subsection, they are inclined opposite to the direction of extent.
Such an arrangement of the outlet ducts may, however, also entail disadvantages. If the change in their orientation and the associated change in the branch-off angle with respect to the coolant duct running in the longitudinal direction and corresponding to the leading edge takes place in a locally abrupt way, then, at the transitional point, possibly relatively large regions between the leading edge and the coolant duct are not penetrated by outlet ducts and therefore also not cooled convectively. This shortcoming then has to be compensated, where appropriate, by cooling air being used to an increased extent in a controlled way. If, instead, the change in orientation of the outlet ducts occurs comparatively continuously, the formation of a film of cooling air flowing along the surface of the blade leaf is impeded in the transitional region, since, there, the cooling air emerges from the film cooling holes almost perpendicularly to the surface and therefore tends to break away from the latter. In this case, too, cooling air has to be supplied to an increased extent, which, in turn, means losses in the available compressor mass flow and diminishes the efficiency of the gas turbine.
An object on which the invention is based is, therefore, to specify a turbine blade of the abovementioned type, for which a particularly reliable and uniform cooling of the leading edge region, at the same time with a cooling air requirement kept particularly low, can be achieved by simple means.
This object is achieved, according to the invention in that the transitional points at which the orientation of the outlet ducts changes, are arranged, in each case for two adjacent rows, to be offset relative to one another in the longitudinal direction.
The invention in this case proceeds from the consideration that, to form an effective cooling film, the cooling medium emerging from the outlet ports in the leading edge region of the blade leaf should have as high a velocity component as possible parallel to the surface. For this reason, the proven orientation of the outlet ducts which runs obliquely with respect to the longitudinal direction should be maintained. In light of the restrictions given in the production of the blade leaf and relating to the access and orientation of the production tools, a change in orientation of the type described is also still desirable for the outlet ducts issuing in the outlet ports along each of the rows in which the outlet ports are arranged. On the other hand, regions with a comparatively highly reduced frequency density of the outlet ducts in the blade wall should be avoided. For this purpose, the situation must be ruled out where the gaps or interspaces belonging to adjacent rows come to lie directly next to one another in the otherwise comparatively regular distribution pattern of the outlet ducts.
This is achieved in that, in each case for two adjacent rows, the associated transitional points are arranged so as to be offset relative to one another in the longitudinal direction. To be precise, the offset gives rise precisely to a local interlacing of the outlet ducts belonging in each case to two adjacent rows and therefore, in terms of all the rows as a whole, to a comparatively homogeneous distribution of the outlet ducts over the entire leading edge region of the blade leaf. In this region, too, therefore, a comparatively good and effective convective cooling of the blade interior is ensured, so that a local overstressing of the material due to overheating is avoided. As compared with known versions, the cooling medium requirement can be kept comparatively low, which has a power-promoting effect for a gas turbine equipped with turbine blades of this type.
A flow behavior, particularly beneficial for effective film cooling, of the emerging cooling medium in the vicinity of the leading edge, in combination with a good convective cooling of the contiguous blade wall, can be achieved in that, in an advantageous development of the invention, the outlet ports in the entire leading edge region are distributed approximately uniformly, in such a way that they lie at the corner points of an imaginary regular grid bent around the leading edge of the blade leaf. This gives rise to a particularly homogeneous wetting of the blade surface with coolant.
The angles of incidence of the outlet ducts with respect to the longitudinal direction are preferably in each case approximately identical for the root-side and tip-side subsections of all the rows of outlet ports. In this case, a value optimized for the film cooling effect and known from tests or calculations can be set.
The concept of the partial interlacing of adjacent film cooling rows can be applied to any number of rows lying next to one another. However, since the radius of curvature of a blade leaf is often relatively small in the vicinity of the leading edge, only a few rows of outlet ports can then be accommodated in the leading edge region. However, even in a preferred embodiment with three rows, a uniform cooling of the leading edge which is particularly economical in terms of the coolant consumption can be achieved. In this variant, the transitional points belonging to the two outer rows are expediently arranged identically and therefore symmetrically to the middle row with respect to the longitudinal direction.
Advantageously, in this case, the transitional point belonging to the middle row is displaced with respect to the two outer rows by the amount of three outlet ports. With this selection, on the one hand, there is a relatively good penetration of the blade wall with outlet ducts in the leading edge region and, on the other hand, the mutual offset is still sufficiently small to ensure that the airstreams emerging in opposite directions in the interlacing region clash with one another only insignificantly.
This optimized arrangement of film cooling bores is particularly advantageous in the case of a guide vane which is provided for use in a gas turbine and which is closed off both at the root-side end and at the tip-side end by possibly bulky and massive platforms which particularly obstruct the access of drilling tools for producing the outlet ducts.
The advantages achieved by means of the invention are, in particular, that the offset to the transitional points in which the orientation of the outlet ducts changes with respect to the longitudinal direction affords a turbine blade which can be produced at lower outlay and which, in the region of the leading edge subjected to particularly high stress, is protected, both on the surface by a uniform cooling air film and in the inner region owing to the convection of cooling air in the outlet ducts distributed approximately homogenously and without any gaps of relatively great extent, against excessive stress caused by heating during operation in a gas turbine. Cooling air can thereby be saved, thus increasing the efficiency of the gas turbine.
An exemplary embodiment of the invention is explained in more detail by means of a drawing in which:
Identical parts are given the same reference symbols in all the figures.
The turbine blade 2 according to
A coolant K is introduced into the blade interior via a number of inlet ports 20 arranged at the lower end of the root section 4. Concepts are also known, however, in which the delivery of the coolant K takes place via the tip-side platform 10. The coolant K is normally cooling air. After the coolant K has flowed through one or more coolant ducts 22 adjoining the inlet ports 20 and located inside the turbine blade 2, it emerges from a number of outlet ports 24 in the region of the blade leaf 12 which are also designed as film cooling holes and correspond with the coolant ducts 22. Thus, in terms of the various kinds of thermal and mechanical load and of the respective space conditions of the blade interior, different regions of the blade leaf 12 present completely different requirements as to the arrangement and configuration of the film cooling holes. In particular, the comparatively highly curved leading edge region 28 directly adjoining the leading edge 14 of the blade leaf 12 requires effective cooling on account of a relatively high load.
In order, on the one hand, to allow a uniform convective cooling of the blade wall 36 and, on the other hand, to promote the formation of a continuous cooling air film, in the exemplary embodiment the outlet ports 24 are arranged along three rows oriented parallel to the leading edge 14, in such a way that they form a regular grid pattern. Moreover, the outlet ducts 34 are inclined with respect to the longitudinal direction L of the turbine blade 2, so that in the region of their outlet ports 24, a flat outlet angle with respect to the blade surface is obtained for the out flowing coolant K. This likewise has a beneficial effect on the generation of a protective cooling air film. As may be gathered from the longitudinal section along the middle row of outlet ports 24 according to
The turbine blade 2 is specifically designed for a particularly reliable cooling of the leading edge region 28, at the same time with the requirement for coolant K being kept particularly low. For this purpose, said transitional points 40 are positioned, offset with respect to one another, in the manner of a partially interlaced arrangement of adjacent film cooling rows. To be precise, the partly sectional perspective view of the leading edge 14 in
An arrangement of outlet ducts 34 and of associated outlet ports 24 is consequently provided which is optimized both in terms of the convective cooling of the blade wall 36 and in terms of film cooling on the surface and which, as compared with the known solutions, is distinguished by a reduced consumption of coolant K and thus increases the efficiency of the gas turbine equipped with turbine blades 2 of this type.
| Number | Date | Country | Kind |
|---|---|---|---|
| EP04015805.7 | Jul 2004 | EP | regional |
