Rotary kinetic fluid motors or pumps – With passage in blade – vane – shaft or rotary distributor...
Reexamination Certificate
1999-12-08
2001-10-30
Lopez, F. Daniel (Department: 3745)
Rotary kinetic fluid motors or pumps
With passage in blade, vane, shaft or rotary distributor...
C416S09700R, C416S19300A
Reexamination Certificate
active
06309175
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to arrangements and a method for cooling platforms in turbomachines, in particular in gas turbines.
BACKGROUND OF THE INVENTION
The efficiency of turbomachines, in particular of gas turbines, can be increased by increasing the cyclic process parameters of the turbomachine. In this case, the relevant cyclic process parameters are the pressure and the temperature of the fluid. The fluid temperatures normally occurring nowadays during the operation of turbomachines, in particular in the turbine inlet region, are already markedly above the admissible material temperatures of the components. In this case, in particular the components forming the flow passage or projecting into the flow passage are directly exposed to the hot fluid flow. As a rule, the heat dissipation of the components, which is brought about by the heat conduction of the material, is not sufficient here in order to avoid an excess temperature of the components. Material temperatures which are too high first of all lead to a drop in the strength values of the material. In the process, crack formation often occurs in the components. In addition, in the event of the melting temperature of the material being exceeded, local or even complete destruction of the component occurs. In order to avoid these fatal consequences, care has to be taken in order to ensure that the component temperatures do not exceed the maximum admissible material temperatures. The flow passage of a turbomachine is often composed of platforms set side by side in an annular manner. The blades of turbomachines are often arranged on such platforms. One blade each is usually made in one piece with one platform. In particular in the case of stators, however, such platforms are often arranged in the form of a shroud of the blading on the blade tips. These platforms are therefore directly exposed to the hot fluid flow. In order not to exceed the maximum admissible material temperature of the platforms, the aim hitherto was normally to achieve over the passage height a temperature profile of the fluid, usually air, discharging from the combustion chamber, in the turbine inlet region. This temperature profile could be achieved via an admixture of cooling fluid into the marginal regions of the hot fluid flow in the discharge region of the combustion chamber. The fluid directly adjacent to the side walls and thus to the platforms, compared with the temperature of the core flow, therefore had a markedly reduced temperature. An excess temperature of the platforms could thus be avoided. On the one hand, a fluid-flow energy content varying over the passage height turns out to be a disadvantage of this method. This fluid-flow energy content varying over the passage height leads in turn to a non-uniform energy conversion in a following rotor and thus to non-uniform loading of the blading over the passage height. Resulting as a further disadvantage of this admixing of cooling fluid to the main flow is a reduction in the efficiency achievable and thus also a reduction in the power density of the turbomachine. For these reasons, a uniform temperature profile over the passage height is aimed at nowadays. In addition, modern combustion chambers are nowadays designed from the aspect of NO
x
reduction in such a way that admixing of secondary combustion air is no longer effected or only slight admixing of secondary combustion air is effected. This results in a very uniform temperature profile over the passage height. This in turn leads to an increase in the thermal loading of the components which are arranged downstream of the combustion chamber, in particular of the side walls and thus of the platforms. Here, it has hitherto been attempted to cool the platforms by blowing out a cooling fluid mostly directly upstream of the platforms. In this case, the cooling fluid is intended to form a cooling film on the top side of the platforms, as a result of which a fluidic separation between the hot fluid and the respective platform occurs. However, the effect of such cooling films, on account of the intermixing with the hot gas, is often quite restricted spatially. Changing pressure conditions of the hot-gas flow or even of the cooling fluid over the load range of a turbomachine likewise lead to a changed cooling film. In addition, in order to ensure adequate cooling, a relatively large cooling-fluid mass flow is required. This in turn leads to a reduction in the efficiency of the turbomachine.
SUMMARY OF THE INVENTION
The object of the invention is to cool platforms in an efficient and reliable manner.
This object is achieved according to the invention in that a cooling passage is arranged for the cooling by means of a cooling fluid at least in one section along a separating gap running between two platforms arranged next to one another. In this case, the cooling passage runs in at least one of the two platforms. The cooling fluid directed in the cooling passage expediently has a lower temperature than the adjacent platforms. As a result, a convectively induced heat transfer occurs between the platforms adjacent to the cooling passage and the cooling fluid and consequently cooling of the platforms occurs. It is found that cooling realized in this way is virtually independent of fluctuations in the operating state of the turbomachine. Furthermore, compared with the other cooling methods described above, a substantially smaller cooling-fluid mass flow is required in order to cool the platforms.
Here, the invention is mostly shown and described in arrangements which are used in turbomachines. In this case, however, this reference to arrangements in turbomachines does not constitute any restriction of the invention to this range of use, but only establishes, by way of example, an actual reference to a technical field. In principle the invention relates to all arrangements of two or more platforms.
Expediently, in this case, the cooling passage, at least in partial sections, runs approximately parallel to the platform surface. This ensures that a large region of the platform is cooled uniformly. It has been found that a temperature distribution which is uniform to a very large extent appears in the cooled regions of the platform. So-called hot-spots in the form of local overheating of the platforms are thereby avoided.
The platforms are often made in one piece or in several pieces with blades arranged on the platforms. The platforms may be arranged on the root or the tip of the blades. The platforms, set side by side, form one side wall or both side walls of the flow passage. In this case, it is advantageous to arrange the cooling passage approximately centrally between the blades. In an especially advantageous manner, the cooling passage is designed with a course approximately similar to the course of the blade profile. It is found that an excess temperature often occurs in the marginal regions and the free regions of the platforms. The free regions of a platform are the regions which in plan view or bottom view are not covered by a blade arranged on the platform. This particular risk to the marginal regions and the free regions with regard to excess temperature may be attributed to the fact that here, on account of small wall thicknesses of the platforms, only slight heat dissipation takes place by heat conduction in the platform itself. In addition, cooling-fluid feed lines for the blade cooling, provided the blade is a fluid-cooled blade, often only run in the centre of the platforms through the platforms into the blades. However, these cooling-fluid feed lines into the blades lead to cooling of the respective platform only in their immediate vicinity. The marginal regions of the platform thus remain uncooled. It has been found that a cooling passage preferably arranged approximately centrally between the blades leads here to optimum cooling, in particular of the marginal regions of the platforms. As a result of the curved course of the profile of the blades, it is also expedient to arrange the cooling passage in the platforms with
Hahnle Hartmut
Hall Kenneth
Harasgama Sriwickrama Prithiviraj
Vogeler Konrad
ABB Alstom Power ( Schweiz) AG
Burns Doane Swecker & Mathis L.L.P.
Lopez F. Daniel
McAleenan James M
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