TIP SHROUD FOR COOLED BLADE OF GAS TURBINE

Abstract: A thin-walled lightweight tip shroud for a moving blade, used in a latter stage of a gas turbine and adapted to smooth a flow of cooling air to improve a cooling efficiency. A tip shroud (11) for a moving blade (10) is provided therein with elongated cooling air holes (13-16) opened at both side surfaces thereof and adapted to discharge the cooling air flowing from the interior of the moving blade (10), and also provided in an upper surface thereof with cooling air holes (20) allowing communication of the interior of the moving blade (10) with a high-pressure side of a direction (R) of a flow of a combustion gas, and adapted to send out cooling air, which flows from a high-pressure side to a low-pressure side to cool a high-stress portion (Y). Also a high-stress portion (X) is cooled in the same manner with cooling air from an adjacent moving blade. The cooling air flows widely owing to the elongated shape of the cooling air holes (13-16) to cool the surface of the tip shroud (11), and the high-stress portions (X, Y) are also cooled effectively owing to the provision of the cooling air holes (20).

Description: TECHNICAL FIELD The present invention relates to a gas turbine cooled blade tip shroud and, more particularly, to a tip shroud for a moving blade, which is made light at a downstream stage of the gas turbine and which is cooled not only from its inside but also from its outside. BACKGROUND ART In the recent years, the gas turbine has advanced to higher temperature and output to have an elongated moving blades. Especially a downstream stage moving blade is remarkably elongated to 50 to 60 cm, for example. This long moving blade has a large weight and accordingly a serious vibration so that the stress to be generated by the centrifugal force at the rotating time becomes far higher than that of the prior art. Therefore, this moving blade is thinned as much as possible so that it may be lighter, and its width is tapered to grow smaller toward the end portion. In Fig. 6 showing an example of the moving blade of the prior art according to the higher temperature, (a) is a longitudinal section, and (b) is a section D - D of (a). In Fig. 6, reference numeral 50 designates a moving blade having a blade root 51 and a hub 53. Numeral 54 designates a hub which has a cavity 55 therein as long as 25 % of the blade length. Numeral 56 designates a number of pin fins protruding inward of the cavity 55 or connected to the two walls. Numeral 57 designates core supporting ribs. Numeral 58 designates multi-holes for feeding cooling air. These multi-holes 58 are arrayed in a large number from the portion of the 25 % blade length, as shown in Fig 6(b), and are formed to a blade end 59. Numeral 60 designates a tip shroud at the leading end. In Fig. 7 showing the tip shroud, (a) is a view taken in the direction of arrows E - E of Fig. 6, and (b) is a view taken in the direction of arrows F - F of (a). In Fig. 7, numeral 61 designates a number of air passages formed along the inner face of the tip shroud 60 and having openings 62. In the moving blade thus constructed, the cooling air having flown from the blade root 51 enters the cavity 55 so that it is disturbed by the pin fins 56 into a turbulent state to cool the hub 54 in the enhanced cooling effect. Then, the cooling air flows through the multi-holes 58 into the air passages 61 of the tip shroud 60 while cooling the blade to cool the tip shroud 60 from the inside until it is finally released from right and left openings 62 to the combustion gas passage. Fig. 8 shows an improvement over the aforementioned moving blade 50 shown in Figs. 6 and 7. In this example of the moving blade, the works of boring the multi-holes are eliminated to improve the workability, and the porosity is improved to improve the cooling efficiency, as has been applied for patent by the Applicant. In Fig. 8, numeral 40 designates a moving blade having a blade root 41 and a hub 42. This moving blade 40 has a cavity which is supported by a number of core supporting ribs 43 extending in the longitudinal direction of the blade. On the inner wall of the cavity, on the other hand, there are provided multiple stages of oblique turbulators 44. Fig. 9 is a section G - G of Fig. 8 and shows the oblique turbulators 44 which are protruded from the inner wall for disturbing the inflows of the cooling air to enhance the cooling efficiency. Numeral 45 designates openings which are formed in the front and back of a tip shroud 46 at the leading end to provide exits for the cooling air. The numeral 46 designates the tip shroud at the leading end. In the moving blade thus constructed, the cooling air 30 flows from below the blade root 41 into the moving blade 40 toward the leading end in the cavity. In this course, the cooling air 30 is disturbed by the oblique turbulators 44 to enhance its cooling effect to extract the heat in the inside of the moving blade 40 until it finally flows from the openings 45 at the leading end of the tip shroud 46 to the combustion gas passage. Here, the tip shroud 46 is similar to that shown in Fig. 7, and its description will be omitted. Figs. 10 and 11 show an improvement over the moving blade 50 of the prior art shown in Figs. 6 and 7. The works of boring the multi-holes are eliminated to improve the workability and the porosity. The example shown in Fig. 10 is also directed to the moving blade of the prior art, as applied for patent by the Applicant. Fig. 10 is a longitudinal section of the moving blade, and Fig. 11 is a section H - H of Fig. 10. In these Figures, numeral 30 designates a moving blade having a blade root 31 and a hub 32. A cavity is also formed in the moving blade 30 and is supported by core supporting ribs 33. Numeral 34 designates a number of pin fins formed in the inside of the cavity. These fins 34 are connected between the two walls of the cavity, as shown in Fig. 11, to disturb the flow of the cooling air like the oblique turbulators 44 provided on the moving blade 40 shown in Figs. 8 and 9 and to increase the heat transfer area thereby to enhance the cooling efficiency. In the moving blade thus constructed, while flowing from below the blade root 31 into the cavity of the moving blade 30 and toward the leading end, the cooling air 30 is disturbed by the pin fins 34 to extract the heat from the pin fins 34 thereby to cool the blade inside, until it finally flows out of the leading end. Here, a tip shroud 36 has a structure similar to that of Fig. 7, and its description will be omitted. In the moving blade of the prior art thus made thin and light and disposed at a gas turbine downstream stage, the pin fins are provided in the cavity up to a 25 % height from the blade root, and the multi-holes are provided from the 25 % height to the tip shroud, so that the cooling air fed from the blade root flows to the leading end portion, while cooling the blade inside, to the leading end portion to cool the inner faces of the tip shroud at the leading end until it finally flows out to the combustion gas passage from the openings formed in the front and rear side faces of the tip shroud. In the moving blade of the prior art improved from the aforementioned multi-hole type moving blade, on the other hand, only the oblique turbulators are provided on the inner wall of the cavity of the moving blade, or only the pin fins are arrayed. In this construction, too, the cooling air is fed from the blade root to cool the inside and the inner face of the tip shroud until it finally flows out to the combustion gas passage from the openings in the side face. In the moving blades of or according to the prior art thus far described, however, the tip shroud is cooled, but its high stress portions (i.e., the X and Y portions shown in Fig. 7(a)) are not sufficiently cooled, although they especially need the cooling. However, the air holes cannot be formed in those portions so as to avoid the stress concentration. Thus, the portions are bottlenecks against the cooling operation because they cannot be cooled by feeding them directly with the cooling air. A prior art gas turbine cooled blade tip shroud to be mounted on a leading end of a thinned and lightened moving blade with the features of the preamble portion of the claim are disclosed in JP 8-200002A. This tip shroud is provided with a plurality of cooling air holes extending through the tip shroud and opening at upstream and downstream sides in a combustion gas flow direction. The cooling air is supplied to these tip shroud cooling air holes through a plurality of cooling air holes provided in the inside of the moving blade. At the connecting portion in the tip shroud between the cooling air holes in the moving blade and the cooling air holes in the tip shroud there is provided a stepped groove extending along the tip of the blade part in the tip shroud and closed at the upper side by a plug to communicate plural blade cooling holes with plural tip shroud cooling holes. DISCLOSURE OF THE INVENTION It i s, therefore, an object of the invention to provide a tip shroud for a thinned and lightened moving blade at a downstream stage of a gas turbine which can be cooled efficiently in its entirety by feeding all over the surface thereof, especially its high stress portions with the cooling air. In order to solve the above-specified first to third objects, according to the invention, there is respectively provided a gas turbine cooled blade tip shroud to be mounted on the leading end of a moving blade and having the features of the claim. In the invention, the cooling air holes are opened in the upper face of the tip shroud on the higher pressure side of the combustion gas passage so that the cooling air having flown from the inside of the moving blade to the upper face of the tip shroud flows along the upper face to the lower pressure side. At the two circumferential end portions of the tip shroud, there are curved peripheral portions, at which the high stress due to the heat is especially concentrated to require especially the cooling treatment. However, these portions cannot be bored because the cooling air holes, if formed, are liable to cause the stress concentration. According to the invention, the cooling air flows along the shroud upper face from the higher pressure side to the lower pressure side due to the pressure difference. In this flowing process, the curved high stress portions can be cooled with the cooling air without forming any hole. In the invention, the cooling air holes in the two side faces of the shroud are formed into the slot shape, and the cooling air holes are also formed on the higher pressure side in the upper face of the tip shroud so that the whole face of the tip shroud can be cooled effectively. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a top plan view of a gas turbine cooled blade tip shroud according to one embodiment of the invention; Fig. 2 is a view taken in the direction of arrows A - A of Fig. 1; Fig. 3 is a view taken in the direction of arrows B - B of Fig. 1; Fig. 4 is a diagram showing the gas turbine cooled blade tip shroud according to the embodiment of the invention and explaining its actions; Fig. 5 is a view taken in the direction of arrows C - C of Fig. 4; In Fig. 6 showing an example of a gas turbine moving blade of the prior art provided with pin fins and multi-holes, (a) is a longitudinal section, and (b) is a section taken in the direction of arrows D - D of (a); In Fig. 7 showing the tip shroud of the gas turbine moving blade shown in Fig. 6, (a) is a view taken in the direction of arrows E - E of Fig. 6, and (b) is a view taken in the direction of arrows F - F of (a); Fig. 8 is a longitudinal section of a gas turbine moving blade according to the technique prior to the invention and provided with inclined turbulator; Fig. 9 is a section taken in the direction of arrows G - G of Fig. 8; Fig. 10 is a longitudinal section of a gas turbine moving blade according to the technique prior to the invention and provided with pin fins; and Fig. 11 is a section taken in the direction of arrows H - H of Fig. 10. BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the invention will be specifically described with reference to the accompanying drawings. Fig. 1 is a top plan view of a gas turbine cooled blade tip shroud according to one embodiment of the invention; Fig. 2 is a view taken in the direction of arrows A - A of Fig. 1; and Fig. 3 is a view taken in the direction of arrows B - B. In Fig. 2: reference numeral 10 designates a moving blade; numeral 11 designates a tip shroud at the leading end portion of the moving blade 10; and numeral 12 designates an upper fin. Numerals 13, 14, 15 and 16 designate cooling air holes opened in the two side faces of the tip shroud 11 and having a slot or elliptical shape, as will be described hereinafter. In the tip shroud 11, there are formed passages which are as wide as the cooling air holes 13 to 16 as in Fig. 7(a). Numeral 20 designates cooling air holes which are formed in the upper face of the moving blade 10, as located on the higher pressure side (or upstream side) in a combustion gas flow direction R with respect to the fin 12 of the tip shroud 11, for releasing the cooling air from the inside of the moving blade 10. Fig. 2 is a view taken in the direction of arrows A - A of Fig. 1 and shows an arrangement of the cooling air holes 13 to 16, as located on the upstream side in the combustion gas flow direction R. As shown, the cooling air holes 13 to 16 are shaped into such a slot as has a wider passage area than that of the simple circular holes of the prior art and a wider area of the tip shroud 11 to allow the cooling air to pass thereby to enhance the cooling effect. Here, these cooling air holes 13 to 16 are exemplified by the slot shape but may be made elliptical. Fig. 3 is a view taken in the direction of arrows B - B of Fig. 1 and shows the downstream cooling air holes 13 to 16 in the combustion gas flow direction R, and their arrangement is similar to that of Fig. 2. The cooling air 30 thus having flown from the moving blade 10 to the leading end flows to the two ends of the tip shroud 11 and has a wide passage so that it can cool the face of the tip shroud 11 effectively. Here, the cooled blade tip shroud in the embodiment of the invention thus far described can be applied with similar effects as the tip shroud of any of the moving blade 50 of the prior art having the pin fins 56 and the multi-holes 58, as described with reference to Fig. 6, the moving blade 40 having only the inclined turbulator 44, as shown in Fig. 8, and the moving blade 30 having only the pin fins 34, as shown in Fig. 10. Here will be described the actions of the gas turbine cooled blade tip shroud of the aforementioned embodiment. Fig. 4 is a top plan view of the tip shroud for explaining the actions and shows tip shrouds 11-1 and 11-2 circumferentially adjoining each other. Fig. 5 is a view taken in the direction of arrows C - C of Fig. 4 and shows the flows of the cooling air over the shroud surface. In Fig. 4, the tip shrouds 11-1 and 11-2 are circumferentially arranged adjacent to each other so that the cooling air 30 from the moving blade 10 passes the slot-shaped cooling air holes 13 to 16 while cooling the inner sides of the tip shrouds 11-1 and 11-2, until it finally flows from the individual two side faces to the combustion gas passage. From the cooling air holes 20 formed in the upper faces of the tip shrouds 11-1 and 11-2 on the higher pressure side with respect to the combustion gas flow direction R, on the other hand, the cooling air from the moving blade 10 flows out to the surfaces of the tip shrouds 11-1 and 11-2. Since the cooling air flows out to the higher pressure side in the combustion gas flow direction R, however, it is forced by the gas flow to a lower pressure side, as indicated by V1, and further to the downstream side, as indicated by V2, over the fin 12. As to a portion of the cooling air V1 to flow out to the lower pressure side in connection with the tip shroud 11-1, the cooling air flows V1 and V2 having passed the fin of the tip cool the surface of the high stress portion X, and a cooling air flow V3 from the tip shroud 11-2 flows while cooling the surface of a high stress portion Y on the higher pressure side of the tip shroud 11-1. Of the high stress portions X and Y of the tip shroud 11-1, therefore, the high stress portion X is cooled with the cooling air flow V1 of its own cooling air holes 20, and the high stress portion Y is cooled with the cooling air flow V3 from the adjoining tip shroud thereby to effect the cooling operation. Fig. 5 is a view taken in the direction of arrows C - C of Fig. 4 and shows the cooling air flow over the upper face of the tip shroud 11-2. As shown, the cooling air flows from the inside of the moving blade 10 via the cooling air holes 20 of the tip shroud 11-2 to the higher pressure side of the combustion gas flow so that it is guided by the pressure difference to flow over the fin 12, as indicated by the flows V1 to V2, along the upper face of the tip shroud 11-2 to the lower pressure side. Even when the pressure for feeding the cooling air is low, therefore, the high stress portions X and Y can be fed with the cooling air by the pressure difference over the upper face of the tip shroud. In the gas turbine cooled blade tip shroud thus far described according to the embodiment of the invention, the slot-shaped cooling air holes 13 to 16 to be opened in the two side faces are provided in the tip shroud 11, and the cooling air holes 20 communicating with the inside of the moving blade 10 are formed in the upper face of the tip shroud 11 on the higher pressure side (or upstream side) in the gas flow direction. As a result, the tip shroud 11 is passed therethrough over its wide area by the cooling air to enhance the cooling effect, and the high stress portions X and Y of the tip shroud 11 are also exposed through the cooling air holes 20 to the cooling air outside of the upper face thereof so that they are effectively cooled to prevent a high stress from occurring. Therefore, the high stress portions X and Y of the tip shroud 11, which cannot be worked to form the cooling air holes, can be fed with the cooling air by making use of the pressure difference at the upper face.

Claims: A gas turbine cooled blade tip shroud (11) to be mounted on a leading end of a thinned and lightened moving blade (10) and having a plurality of cooling air holes (13,14,15,16) provided in two side faces on upstream and downstream sides in a combustion gas flow direction (R) of a combustion gas passage and adapted to receive cooling air flowing in the inside of said moving blade (10) from the blade root to the leading end portion and to release the cooling air from said cooling air holes (13,14,15,16), characterized in that said cooling air holes (13,14,15,16) provided in the two side faces on upstream and downstream sides in the combustion gas flow direction (R) of the combustion gas passage are formed into a slot shape along the side faces of the tip shroud (11); and cooling air holes (20) are opened in the upper face of the tip shroud (11), communicating with the inside of said moving blade (10) and positioned on the upstream side of the combustion gas flow direction (R) so that cooling air having flown in the inside of said moving blade (10) to the leading end portion thereof is released at the cooling air holes (20) at the upper face and flows along the tip shroud upper face to the downstream side of the combustion gas flow direction (R) to thereby cool high stress portions (X,Y) of the circumferential end portions of the tip shroud (11).

Inventors: FUKUNO HIROKI, ITO EISAKU, TOMITA YASUOKI, FUKUNO, HIROKI, ITO, EISAKU, TOMITA, YASUOKI, FUKUNO, Hiroki-Takasago Machin. Works Mitsubishii, ITO, Eisaku-Takasago Machin. Works Mitsubishi ind., TOMITA, Yasuoki-Takasago Machin.Works Mitsubishii
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI HEAVY INDUSTRIES, LTD.
Application year: 1998
Main classification: F01D5
IPC codes: F01D5, F02C7, F01D11