Gas turbine blade

Abstract: In the cooling system for the gas turbine blade, the present invention ensures cooling of the trailing edge part (7,8) of the blade for which machining is difficult, while aiming at improvement of the thermal efficiency. The steam cooling structure for carrying out heat recovery-type steam cooling is employed to the leading edge part (1) and the central part (3) of the blade where machining is easy because of its large thickness, and the convection cooling and film cooling (7,8) are employed for the trailing edge part of the blade where the thickness is small, using steam cooling and air cooling at the same time.

Description: FIELD OF THE INVENTION AND RELATED ART STATEMENT The present invention relates to a gas turbine blade which is cooled by concurrently using two types of coolants, i.e., steam and discharged air from a compressor. Cooled blades which are used in a high-temperature gas turbine has a passage of cooling air in the interior of the blades. The blades are cooled by low-temperature air flowing through the passage in the blade, and the temperature of the blade is suppressed to a tolerable temperature level which is lower than the temperature of the combustion gas. In the conventional air-cooling system, as shown in the vertical sectional view of Figure 4(a) and in the sectional view along the line B-B of Figure 4(b), the cooling air supplied to the blade passes through the internal cooling passage from the root part of the blade to the inner part of the blade and is discharged into the main gas stream as a unidirectional flow from the holes in the blade which open toward the main stream. Since there is an upper limit of thermal efficiency in the conventional system, the use of steam in place of air has been proposed in recent years for further improving the thermal efficiency of the conventional system. When the steam cooling is adopted, the steam is not discharged into the main stream and recovered, and heat is recovered from this recovered steam by collecting the heat gained by cooling the gas turbines with the use of a steam turbine. The overall efficiency of the plant may be maintained and the turbine efficiency can be improved by reducing the amount of cooling medium blowing out into the gas turbine. When the steam is recovered by the steam turbine, a reduction of efficiency can be minimized if pressure losses caused by the cooling of gas turbine may be reduced and the heat is recovered at a higher pressure stage of the steam turbine. However, as may be readily understood from Figure 4 which shows an example of air cooling, the trailing edge part of a moving blade in a gas turbine is made thin so as to reduce aerodynamic losses. It would be difficult to provide convection cooling structures such as serpentine cooling or impinging cooling in the interior of this thin part. A gas turbine rotor blade having a combined steam and aircooling is disclosed in the document GB-A-2 307 520. OBJECT AND SUMMARY OF THE INVENTION The object of the present invention is to provide a gas turbine blade in accordance with claim 1. The present invention has been devised to solve the above-mentioned problems and provides a gas turbine moving blade which comprises a blade part, a platform part, a root part, a steam cooling structure provided in the leading edge part and in the central part of the blade for heat recovery-type steam cooling, and a convection and film cooling structure which introduces air discharged from compressor to the trailing edge of the blade. That is, for the leading edge and central parts at which the blade thickness is large, steam for cooling is supplied into such a cooling passage as a serpentine flow passage, and heat is recovered. On the one hand, for the trailing edge part where the thickness of the blade is small, the air discharged from the compressor is introduced as cooling air from a cooling passage inlet port which is provided at the shank part and the like of the blade, then convection cooling and subsequent film cooling are performed. Adopting such cooling structure with a combination of air and steam cooling, the effective cooling is achieved without facing difficulties in machining. BRIEF DESCRIPTION OF THE DRAWINGS An embodiment according to the present invention will be described in further detail with reference to the accompanying drawings, in which: Figure 1 is a sectional view showing the cooling structure of the gas turbine blade part, according to one embodiment of the present invention; Figure 2 is a plan view showing the cooling structure of the platform of the gas turbine blade of Figure 1; Figure 3 is a sectional view, along the line A-A of Figure 2; and Figure 4 shows the conventional blade cooling structure, and Figure 4(a) is a vertical sectional view and Figure 4(b)is a sectional view, along the line B-B of Figure 4(a). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described, with reference to Figure 1 to Figure 3. Figure 1 shows a vertical sectional view of the gas turbine blade; Figure 2 shows the cooling structure of the platform; and Figure 3 shows a sectional view of the platform convection cooling holes. In the figures, a blade part 1, a platform 2, a cooling serpentine passage 3 formed over the leading edge part to the central part of the blade, a supply port 4 for the cooling steam, a recovery port 5 for the cooling steam, a multi-hole type cooling passage 6 provided on platform 2, a cooling air passage 7 provided in the trailing edge part of the blade, convection cooling holes 8 provided in the trailing part of the blade continuing from the cooling air passage 7 of the trailing part of the blade, an cooling air passage entrance 10, a root part 11 of the blade, and an arrow 12 showing the inflow of the discharged air from a compressor are shown. The supply port 4 for the cooling steam and the recovery port 5 for the cooling steam are provided in the root part 11 of the blade and are in communication with the cooling serpentine passage 3. In the embodiment having the above constitution, the blade-cooling steam is supplied from a rotor system via the supply port 4 for the cooling steam of the root part 11 of blade. Further, this blade-cooling steam, after cooling by flowing through the internal cooling serpentine passage 3 in the blade 1 along the arrow, is recovered from the recovery port 5 for the cooling steam in the root part 11 of the blade to the rotor system. At the same time, the platform 2 has a branched flow of steam on the downstream side from the supply port 4 for the cooling steam. After having performed convection cooling with the steam flowing in the multi-hole convection cooling passage 6, the branched flow of steam is mixed with the blade cooling steam on the upstream side of the recovery port 5 for the cooling steam and is then recovered. On the one hand, in the trailing edge part of the blade, the air 12 discharged from compressor is supplied from the cooling air passage entrance 10, and the air 12 passes through the cooling air passage 7. After performing cooling through the convection cooling holes 8 in the trailing edge part of the blade, the air 12 is discharged into the main stream. According to the present embodiment, cooling steam supplied from the rotor system is used to cool the platform 2 as well as the leading edge part and the central part of the blade part 1 while it led into the internal convection cooling passage and flows through the multi-hole cooling passage 6 and the serpentine passage 3. After having been steam cooled by means of the serpentine passage 3 and the multi-hole type cooling passage 6, the cooling steam is again returned to the rotor system, together with the heat which has been removed as a result of cooling. The collected heat is then recovered outside the blade system. The heat gained by the steam after cooling the blade is recovered by a steam turbine (not shown). The performance of the gas turbine is prevented from deteriorating, and an improvement in the gas turbine efficiency can be achieved by not allowing the coolant to enter into the gas turbine. The efficiency of the plant as a whole can be enhanced in combination with these effects. In addition, with regard to the trailing edge part of the blade, the air 12 discharged from compressor is led to the cooling air passage entrance 10 which is provided at a shank part and led through the cooling air passage 7 extending from the blade root to the blade end. The air 12 passes through the convection cooling holes 8 provided in the trailing edge part of the blade and the film cooling holes provided on the blade surface to perform cooling. Since this cooling air passage 7 and the convection cooling holes 8, unlike the serpentine passage 3, does not amount to a large volume, it is not difficult to fabricate such passage and holes. The temperature of the metal can be suppressed below the tolerable temperature level by the film cooling. Although the present invention has been described with reference to an embodiment illustrated as in the foregoing sections, it is obvious that the present invention is not limited to such an embodiment, but a variety of modifications may be added to its specific structure, within the range of the present invention.

Claims: A moving gas turbine blade comprising: a blade part (1), a platform part (2), a root part (11), a steam cooling structure for performing thermal recovery-type steam cooling of a leading edge part and a central part of the blade part with steam, the steam cooling structure comprising a cooling passage (3) for supplying the cooling steam in the leading edge part and the central part of the blade (1) ; an air cooling structure for introducing air (12) discharged from a compressor for the cooling of a trailing edge part of the blade, the air cooling structure comprising a cooling air passage (7) for introducing the air (12) discharged from the compressor into the trailing edge part of the blade (1) and holes (8) provided in a wall of the blade part so as to let the air flow from the cooling air passage (7) to the outside of the blade part; and characterized by : a steam cooling structure for the platform part, the platform part (2) of the blade having at least one passage (6) for conducting a cooling steam flow branched from the cooling steam for cooling the blade part. A gas turbine blade according to claim 1 wherein the steam cooling passage (3) for cooling the leading edge part and central part of the blade part (1) is of serpentine form. A gas turbine blade according to either claim 1 or claim 2 wherein the cooling passage (6) in the platform part (2) is a multi-hole type passage. A gas turbine blade according to any one preceding claim wherein a supply port (4) for the cooling steam and a recovery port (5) for the cooling steam are both provided in the root part (11) of the blade and are in communication with the steam cooling passage (3). A gas turbine blade according to any one preceding claim, wherein an inlet (10) for said cooling air (12) is provided in said root part (11). A gas turbine blade according to claim 1 wherein the trailing edge part of the blade is cooled by convection and film cooling. A gas turbine blade according to any one preceding claim from 3 to 6 wherein the cooling passages (6) for steam cooling the platform (2), connect with the steam inlet port (4) at a leading edge side of the blade and with a steam outlet port (5) at a central part of the blade in the root (11).

Inventors: AOKI SUNAO, SUENAGA KIYOSHI, UEMATSU KAZUO, AOKI, SUNAO, SUENAGA, KIYOSHI, UEMATSU, KAZUO, Aoki, Sunao, Mitsubishi Heavy Ind. Ltd.,, Suenaga, Kiyoshi, Mitsubishi Heavy Ind. Ltd.,, Uematsu, Kazuo, Mitsubishi Heavy Ind. Ltd.,
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI HEAVY INDUSTRIES, LTD.
Application year: 1998
Main classification: F01D5
IPC codes: F01D5