The invention relates generally to gas turbine engines and more particularly, to cooling systems used to supply cooling medium into gas turbine components. The modern trends of gas turbines development focus on achievement of a maximum power and efficiency output by increasing turbine inlet gas temperature as well as a compressor pressure ratio. Due to the contribution and the development of gas turbine cooling systems, the gas turbine entry temperature has been over doubled over the last 60 years .

However, operation at very high temperatures reduces the life time of gas turbine components such as gas turbine blades, gas turbine vanes, gas turbine struts, etc., that are susceptible to damage by the hot working gas.

Therefore, cooling of such gas turbine components is necessary to reduce their temperature to acceptable levels for the materials to increase the thermal reliability and lifetime of the gas turbine engine. A wide range of cooling systems has been applied in the past; however, the main goal is to keep the entire gas turbine component such as a gas turbine blade, a gas turbine vane, a gas turbine struts, etc. cool enough and also to ensure that temperature gradients within such gas turbine components (which might lead to thermal stresses) are kept to an acceptable level.

Such cooling systems can be classified in two major sections: the internal, where the heat is removed by a variation of convection and / or impingement cooling configurations, where high velocity air travels inside the gas turbine vanes and blades, and the external cooling, where cold air is injected through the film cooling holes on the external surface of the gas turbine components in order to create a thin film cooling layer . The internal cooling systems are similar in that each cooled gas turbine component is hollow and incorporates one or more internal cooling passages. During gas turbine operation, a supply of pressurized air is directed from the compressor section through these passages to provide the desired cooling effect. The air is directed into the gas turbine component through one or more openings provided in the root. Being under a pressure greater than that within the turbine casing, the cooling agent continues to travel through the internal passages within the airfoil section and is then exhausted into the turbine gas stream. In this way, the gas turbine component is cooled, and sustained, efficient gas turbine operation is made feasible.

FIG 1 illustrates a prior art cooling supply system for gas turbine component cooling on the example of a gas turbine vane. The gas turbine component 1, that is a gas turbine vane, is a hollow gas turbine component having an end wall 2 connected, in this particular example, to a gas turbine stator 3. The gas turbine component 1 is heated by the stream 4 of working gas. The end wall 2 of the gas turbine vane 1 has a cooling medium supplying orifice 5 for the cooling agent 6 supply. During the gas turbine operation the cooling agent 6 provided into the gas turbine stator 3 (the way of providing the cooling medium into the gas turbine rotor is not shown on FIG 1) flows through the cooling agent supplying orifice 5 at the end wall 2 and then cools the gas turbine vane 1.

For the full load mode when the gas turbine works in its full capacity the relative mass flow of the cooling medium 6 is exactly what is needed to get the gas turbine vane 1 cooled. However in the beginning of the operation and / or for the partial load mode the relative mass flow of the cooling medium 5 is redundant. Therefore it leads to superfluous cooling of the gas turbine vane 1. As a result of such superfluous cooling of the gas turbine component 1 the power and efficiency output of the gas turbine for the partial load mode deteriorate . In most cases of cooling systems the required relative mass flow of cooling medium is determined for the gas turbine operating "hot" mode with a full load when the temperature of the working gas and gas turbine components that are to be cooled are maximum one .

However in many cases the gas turbine operates on the moderate operating modes with a partial load when the cooling is required for the gas turbine components, but not as significant as in case of full load and "hot" operating mode. In such cases the redundant relative mass flow of the cooling medium 6 results in the deterioration of the gas turbine power and efficiency output for the said mode.

The above mentioned disadvantage of the cooling supply system might be eliminated by using a special valve (DE 10009655 CI) in order to adjust the relative mass flow of the cooling agent for the gas turbine components under the different operating modes. The said valve should be the component of a total control system. However such improved cooling supply system has its own disadvantages, namely: there is no possibility to cut off the cooling mass flow completely, because in this case the hot working gas can inflow into the casing that is undesirable. Moreover the presence of the above mentioned valve makes the gas turbine design and the control system more complicated.

In the light of the foregoing discussion, it is evident that there is a strong need of an easy, convenient and appropriate cooling supply system for gas turbine components.

The object is solved by a supply system for gas turbine component cooling as defined in claim 1.

Consequently, the present invention provides a supply system for gas turbine component cooling, wherein the gas turbine component is a hollow component that is required to be cooled, for example a gas turbine blade, a gas turbine vane, a gas turbine strut, etc. The supply system comprises at least one orifice for supplying cooling agent into the gas turbine component and arranged at an end wall of the gas turbine component. In addition to that the supply system comprises at least one bimetallic component arranged in the area of the at least one orifice. Furthermore the at least one bimetallic component is adapted to open and close the at least one orifice depending on the temperature of the gas turbine component .

The present invention is based on the insight that under changing thermal conditions every metal expands or contracts according to a fixed thermal expansion coefficient. Hence the bimetal, a component made of two connected strips of different metals (e.g. steel and zinc) , bends when the temperature changes. Taking into account the fact that the bimetallic component is in thermal contact with the gas turbine component, the bimetal component bends when the temperature of the gas turbine component grows . Such bending of the bimetallic component makes the at least one orifice open and more cooling agent are supplied into the gas turbine component . As soon as the temperature of the gas turbine component goes down the bimetallic component closes the at least one orifice. Therefore no overcooling of the gas turbine component occurs and the corresponding cooling agent mass flow is saved.

Thus, the present invention is proposed to provide a new supply system for cooling a gas turbine component.

Further embodiments of the present invention are subject of the further sub-claims and of the following description, referring to the drawings.

In a possible embodiment of the supply system a dead end of the at least one bimetallic component is fixed at the end wall of the gas turbine component and a loose end of the at least one bimetallic component is in front of the at least one orifice. Furthermore the loose end of the at least one bimetallic component is adapted to move depending on the temperature of the at least one bimetallic component. This feature allows to arrange the at least one bimetallic component in the area of the at least one orifice and adapt it to open and close the at least one orifice depending on the temperature of the gas turbine component . In another possible embodiment of the supply system a layer of the at least one bimetallic component which is closer to the end wall of the gas turbine component has larger value of the thermal expansion coefficient in comparison with another layer of the at least one bimetallic component. This feature allows providing the bimetallic component to bend in such way that opens the at least one orifice, i.e. in the direction from the surface of the end wall of the gas turbine component .

In possible embodiment of the supply system there is an inlet slot in front of the at least one orifice between the at least one bimetallic component and the end wall of the gas turbine component. Furthermore the cross section of the inlet slot is less than the cross section of the at least one orifice. The inlet slot always exists independently whether the bimetallic component is in the state when the at least one orifice is closed or open by the respective bimetallic component .

This feature allows providing minimal cooling agent into the gas turbine component when the at least one bimetallic component is in the state when the at least one orifice is closed by the respective bimetallic component, i.e. the bimetallic component covers the at least one orifice. Therefore some minimal cooling of the gas turbine component is still provided.

In possible embodiment of the supply system there is a protrusion on the end wall of the gas turbine component along the contour of the at least one orifice on which the loose end of the at least one bimetallic component is situated when the at least one bimetallic component is in the state when the at least one orifice is closed by the respective bimetallic component.

This feature allows preventing any access of the cooling agent into the gas turbine component when the at least one bimetallic component is in the state when the at least one orifice is closed by the respective bimetallic component. The cooling agent full cut-off can be achieved, that can be desirable for some gas turbines.

In possible enhanced embodiment of the supply system the end wall of the gas turbine component has at least one additional orifices for guiding cooling agent into the gas turbine component wherein the at least one additional orifice is arranged in such way that it is not covered by the at least one bimetallic component. Having such additional orifice not covered by the at least one bimetallic component provides access of minimal cooling agent into the gas turbine that can be desirable for some gas turbines.

In possible enhanced embodiment of the supply system the at least one bimetallic component has at least one further orifice for guiding cooling agent into the gas turbine component wherein the cross section of the at least one further orifice is less than the cross section of the at least one orifice. Therefore even in case when the at least one bimetallic component is in the state when the at least one orifice is closed by the respective bimetallic component, there is an access of some cooling agent into the gas turbine component. This feature allows avoiding overheating the gas turbine component in case the at least one orifice is tightly closed by the bimetallic component, since cooling agent is still provided into the gas turbine component.

In possible enhanced embodiment of the supply system the at least one orifice is covered by the at least one bimetallic component in part .

This feature allows avoiding overheating of the gas turbine component when the at least one bimetallic component is in the state when the at least one orifice is closed by the respective bimetallic component.

For a more complete understanding of the present invention and advantages thereof, reference is now made to the following description taken in accompanying drawings . The invention is explained in more detail below using exemplary embodiments which are specified in the schematic figures of the drawings, in which: Fig. 1 shows a block diagram of a supply cooling system (prior art) ;

Fig. 2 shows a block diagram of the supply system for gas turbine component cooling according to the present invention; Fig. 3 shows a block diagram of the supply system for gas turbine component cooling according to the present invention;

Fig. 4 shows a block diagram of an embodiment of the supply system for gas turbine component cooling according to the present invention;

Fig. 5 and Fig. 6 show a block diagram of another embodiment of the supply system for gas turbine component cooling according to the present invention;

Various embodiments are described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purpose of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more embodiments. It may be evident that such embodiments may be practice without these specific details.

FIG 2 illustrates the supply system 7 for cooling a gas turbine component 1 according to the present invention. FIG 2 shows a gas turbine vane as the gas turbine component 1 that is heated by the stream 4 of the working gas. However the present invention is applicable to any hollow component inside the gas turbine that is required to be cooled down. Such gas turbine components 1 can be a gas turbine blade, a gas turbine vane, a gas turbine strut, etc.

The supply system 7 comprises at least one orifice 5 for supplying cooling agent 6 into the gas turbine component 1 and arranged at an end wall 2 of the gas turbine component 1.

Additionally the supply system 7 comprises at least one bimetallic component 8 arranged in the area of the at least one orifice 5 wherein the at least one bimetallic component 8 is adapted to open and close the at least one orifice 5 depending on the temperature of the gas turbine component 1. The supply systems 7 can comprise more than one orifice 5 and more than one bimetallic component 8. The at least one bimetallic component 8 can be adapted to open and close one or more orifices 5.

In some embodiments of the supply system 7 the at least one orifice 5 can be covered by the at least one bimetallic component 8 in part .

Also at least one additional orifice 5 for guiding cooling agent 6 into the gas turbine component 1 can be arranged in the end wall 2 of the gas turbine component 1 in such way that the at least one additional orifice 5 is not covered by the at least one bimetallic component 8. Such orifices 5 that are not covered by the bimetallic component 8 at all and / or covered by the bimetallic component 8 in part work as safety openings.

In addition to that the at least one bimetallic component 8 can have at least one further orifice 9 (as it is shown on FIG 3) for guiding cooling medium 6 wherein the cross section of the at least one further orifice 9 is less than the cross section of the at least one orifice 5.

The number of orifices 5 and their parameters, e.g. size, shape, etc., location of the orifices 5, the number of bimetallic components 8 and their parameters, e.g. size, shape, materials, etc., depends on the required working regimes of the gas turbine and should be defined by experts.

Therefore it might be possible to select appropriate combination of the orifices 5, additional orifices 5, further orifices 9 and bimetallic components 8 to provide required cooling of the gas turbine component 1 appropriate for different operational modes of the gas turbine.

Bimetals are well known. They refer to an object that is composed of two separate metals joined together. Instead of being a mixture of two or more metals, like alloys, bimetallic objects consist of layers of different metals. The bimetallic component 8 comprises two metallic layers 10, 11. The bimetallic component 8 should arranged in the area of the at least one orifice 5 in such way that a layer 10 of the at least one bimetallic component 8 which is closer to the end wall 2 of the gas turbine component 1 has larger value of the thermal expansion coefficient in comparison with another layer 11 of the at least one bimetallic component 8. Such placement of the bimetallic component 8 provides bending of the bimetallic component 8 in such way that it opens the at least one orifice 5, i.e. in the direction from the surface of the end wall 2 of the gas turbine component 1.

A dead end 12 of the at least one bimetallic component 8 is fixed at the end wall 2 of the gas turbine component 1 and a loose end 13 of the at least one bimetallic component 8 is in front of the at least one orifice 5. Therefore the loose end 13 of the at least one bimetallic component 8 is adapted to move depending on the temperature of the at least one bimetallic component 8.

The supply system 7 works as following: in the beginning while the gas turbine component 1 is cold, the at least one bimetallic component 8 is in the state when the at least one orifice 5 is closed by the respective bimetallic component 8.

Hence the bimetallic component 8 is in thermal contact with the gas turbine component 1, the bimetallic component 3 bends and opens the at least one orifice 5 for further supplying cooling agent 6 into the gas turbine component 1 as soon as the gas turbine component 1 gets heated. Intermediate states of the bimetallic component 8 are possible, so the cooling of the gas turbine component 1 is provided on the required level appropriate for the respective operational mode of the gas turbine .

For the full load mode of the gas turbine the thermal bending of the bimetallic component 8 becomes maximum, so maximum of cooling agent 6 arrives into the gas turbine component 1. Therefore the gas turbine component 1 is getting cooled down.

For the partial load mode of the gas turbine the thermal bending of the bimetallic component 8 exists, but not maximum. So cooling agent 6 arrives into the gas turbine component, however not maximum amount of it. Therefore cooling of the gas turbine component 1 is provided, but no overcooling of the gas turbine component 1 occurs .

In case temperature of the gas turbine component 1 goes down, the bimetallic component 8 become straight, and closes the at least one orifice 5. Therefore the cooling agent 6 does not get inside the gas turbine component 1. As a result no overcooling of the gas turbine component 1 occurs.

Such behavior of the bimetallic component 8 is well known: under changing thermal conditions every metal expands or contracts according to a fixed thermal expansion coefficient. Hence the bimetal, a component made of two connected strips of different metals (e.g. steel and zinc), bends when the temperature changes.

FIG 4 illustrates possible embodiment of the supply system 7 for cooling of a gas turbine component 1 according to the present invention wherein there is an inlet slot 14 in front of the at least one orifice 5 between the at least one bimetallic component 8 and the end wall 2 of the gas turbine component 1. The cross section of the inlet slot 14 is less than the cross section of the at least one orifice 5.

The inlet slot 14 always exists independently whether the bimetallic component 8 is in the state when the at least one orifice 5 is closed or in the state when the at least one orifice 5 is open. The size of the inlet slot 14 should be defined by experts.

The supply system 7 works as it was described above. However in the state when the at least one orifice 5 is closed by the respective bimetallic component 8, still there is an access of some cooling agent 6 into the gas turbine component 1. Therefore some minimal cooling of the gas turbine component 1 is still provided.

FIG 5 and FIG 6 illustrate another possible embodiment of the supply system 7 for cooling of a gas turbine component 1 according to the present invention wherein there is a protrusion 15 on the end wall 2 of the gas turbine component 1 along the contour of the at least one orifice 5 on which the loose end 13 of the at least one bimetallic component 8 is situated when the at least one bimetallic component 8 is in the state when the at least one orifice 5 is closed by the respective bimetallic component 8.

The supply system 7 works as it was described above for the FIG 2. However in the state when the at least one orifice 5 is closed by the respective bimetallic component 8, there is no access of any cooling agent 6 into the gas turbine component 1. Such protrusion 15 provides more close contact of the at least one bimetallic component 8 and the end wall 2 of the gas turbine component 1. As a result of it no leaks of the cooling agent 6 inside the gas turbine component 1 occurs in the state when the at least one orifice 5 is closed by the respective bimetallic component 8.

The parameters of the protrusion 15 such as size, shape, etc. should be defined by experts.

While the invention has been illustrated and described in detail with the help of preferred embodiment, the invention is not limited to the disclosed examples. Other variations can be deducted by those skilled in the art without leaving the scope of protection of the claimed invention.

Reference numerals

1 - gas turbine component

2 - end wall

3 - gas turbine stator

4 - working gas

5 - orifice

6 - cooling agent

7 - supply system for gas turbine component cooling

8 - bimetallic component

9 - further orifice

10, 11 - layers of the bimetallic component

12 - dead end of the bimetallic component

13 - loose end of the bimetallic component

14 - inlet slot

15 - protrusion