Gas turbine stationary blade

Abstract: A gas turbine stationary blade with impingement holes of different diameters in order to prevent clogging is presented. Impingement holes (4b) on dorsal side of the front insert (2) and film cooling holes (12) of the blade have diameters larger than those of other holes, so that dusts in cooling air are caused to flow out to prevent clogging of the holes.

Description: BACKGROUND OF THE INVENTION: Field of the Invention: The present invention relates generally to a gas turbine stationary blade and more particularly to a gas turbine stationary blade structured such that a blade leading edge is improved of shape so as to blow a blade cooling air with an enhanced efficiency, a thermal stress concentration is avoided and a blade assembling is facilitated. Description of the Prior Art: Fig. 2 is a cross sectional view showing a representative first stage stationary blade of a gas turbine in the prior art. In Fig. 2, numeral 20 designates a first stage stationary blade, numeral 21 designates an outer shroud and numeral 22 designates an inner shroud. Numerals 20a, 20b, 20c, 20d, 20e designate cooling air holes, respectively, wherein the hole 20a is provided in a blade leading edge, the hole 20b in a blade trailing edge, the hole 20c in a blade leading edge portion, the hole 20d in a blade central portion and the hole 20e in a blade trailing edge portion. Within the stationary blade 20, there are provided a passage 23 in the blade leading edge portion, a passage 24 in the blade central portion and a passage 29 in the blade trailing edge portion. An insert 25 is provided being inserted into the passage 23 and an insert 26 is provided being inserted into the passage 24. The inserts 25, 26 are so provided in the passages 23, 24, respectively, with predetermined spaces being maintained from inner wall surfaces of the respective passages 23, 24 and are supported at a multiplicity of points. Both of the inserts 25, 26 are made in hollow cylindrical members and there are bored a multiplicity of air blowing holes 27, 28 in and around entire walls of the inserts 25, 26, respectively. In the mentioned first stage stationary blade, cooling air 30, 31, 32 is led into the stationary blade 20 from a turbine casing space (not shown) through the outer shroud 21, wherein the cooling air 30 flows into the insert 25 on the leading edge side to then flow out of the air blowing holes 27 of the insert 25 into a space formed between an inner wall of the passage 23 and an outer wall of the insert 25 to effect an impingement cooling of the inner wall of the passage 23 and then flows out of the cooling air holes 20c bored in the blade onto an outer surface of the blade to effect a shower head cooling and a film cooling of the blade outer surface. The cooling air 31 likewise flows into the insert 26 to then flow out of the air blowing holes 28 of the insert 26 into a space formed between an inner wall of the passage 24 and an outer wall of the insert 26 to effect the impingement cooling of the inner wall of the passage 24 and then flows out of the cooling air holes 20d bored in the blade onto the outer surface of the blade to effect the film cooling of the blade outer surface. Also, the cooling air 32 flows into the passage 29 on the trailing edge side to cool a rear portion of the blade and flows out of the cooling air holes 20e of the blade trailing edge portion onto the outer surface of the blade for the film cooling thereof. In the first stage stationary blade as described above, there occurs a non-uniformity of the outflow air at the blade leading edge to cause an irregularity in the air flow velocity and this often results in enlarging a pressure loss or this may result in causing a back flow of the cooling air according to the case. Also, there occurs a clogging of the air blowing holes of the insert within the blade due to dusts in the cooling air and this results in a problem to enlarge the pressure loss. Also, when the insert is to be assembled into the blade, there are the multiplicity of points to fix the insert in the air passage and also the work space therefor is narrow, hence the assembling error becomes large and a lot of time is required for the assembling. Further, in terms of a thermal stress, connecting portions of the blade to the outer shroud and the inner shroud are structured to have only small fillet curves, hence the thermal stress may concentrate there to cause cracks easily. Thus, in the recent tendency of the gas turbine operated in a higher temperature, it is strongly desired to solve the mentioned problems to enhance a reliability of the stationary blade. US-A-3 240 468 discloses a gas turbine stationary blade having a porous skin for transpiration cooling with provision for channelling more or less coolant to various portions of the blade in relation to gas temperatures, pressures and velocities prevailing in localized regions. This blade comprises a plurality of passages provided in the blade from a leading edge side to a trailing edge side thereof and plural cooling air holes provided in the blade skin. The passages provided in the blade are formed by a single piece hollow shell inserted into the interior of the blade and fixed therein. Air blowing holes provided in this shell are arranged in several groups provided in a dorsal side rear portion of the shell wherein holes of a first group have a diameter that is larger than that of holes of a second group. The holes of each respective first and second group are arranged in a length-wise direction of the blade. SUMMARY OF THE INVENTION It is an object of the present invention to provide a gas turbine stationary blade having a structure improved such that film cooling holes through which the air flows out are prevented from clogging, thereby cooling efficiency of the blade is enhanced. In order to achieve this object, the present invention provides a gas turbine stationary blade as defined by claim 1. Preferred embodiments are defined in the dependent claims. In the invention, there is considered a case where fine dusts contained in the cooling air are going to flow out of the air blowing holes of the insert and this may cause a clogging but, of the air blowing holes of the insert, hole diameters of those holes in the dorsal side rear portion of the insert where the dusts may stagnate comparatively easily are made larger than those of the other holes and also hole diameters of the cooling holes of the blade near the air blowing holes having such larger diameters are made larger likewise, thereby the dusts in the insert are caused to flow out easily of the air blowing holes and the cooling holes both having such larger hole diameters. Hence, there occurs no case of the clogging of the air blowing holes of the insert and the cooling holes of the blade due to the dusts and a reliability of the cooling is enhanced remarkably. In an embodiment, the insert in each of the passages is supported only at two places and as compared with the prior art case where there are many points of supporting, the positioning for the assembling becomes facilitated, the man-hours of the blade assembling are reduced and the fitting accuracy is enhanced as well, which results in enhancing a blade reliability. In a preferred embodiment, a projection is formed on the blade leading edge and by this projection, the blade leading edge where there is especially a large thermal load can be made smaller in size. The blade leading edge in the prior art is substantially of a circular shape and cooling holes through which cooling air is blown are arranged in plural rows in this portion. But in this embodiment, as mentioned above, the projection having the smoothly curved surface is provided projecting from the blade leading edge where the thermal load is high and this portion of the blade is made smaller, thereby the number of rows of the cooling holes can be reduced as well. In another embodiment, the curved surface of the projection is formed to an elliptical curve on an ellipse long axis so that the projection may be made smaller in size and the cooling air may be flown out effectively of the projection so made smaller, In a further embodiment, the curved surface of the blade leading edge is formed to an elliptical curve on an ellipse long axis and the cooling air flowing out of the cooling holes does not become turbulent on the blade dorsal side to flow smoothly along the curved surface of the blade dorsal portion, thereby an effective film cooling becomes possible. BRIEF DESCRIPTION OF THE DRAWINGS: Fig. 1 is a cross sectional view of a gas turbine stationary blade of one embodiment according to the present invention. Fig. 2 is a cross sectional view showing a representative first stage stationary blade of a gas turbine in the prior art. Fig. 3 is a schematic view showing a shape of a blade leading edge portion of the embodiment of Fig. 1, wherein Fig. 3(a) shows the shape of the present invention and Fig. 3(b) shows that of the prior art. Fig. 4 is a detailed view of a projection of a blade leading edge of the embodiment of Fig. 1. Fig. 5 is a graph showing a cooling air flow velocity in the gas turbine stationary blade of the embodiment of Fig. 1. DESCRIPTION OF THE PREFERRED EMBODIMENTS: Herebelow, embodiments according to the present invention will be described concretely with reference to figures. Fig. 1 is a cross sectional view of a gas turbine stationary blade, especially a first stage stationary blade, of one embodiment according to the present invention. In Fig. 1, numeral 10 designates a stationary blade and numeral 1 designates a projection, which is provided projecting from a portion on a ventral side of a blade leading edge. The projection 1 is formed having a smoothly curved surface. In the stationary blade 10, like in the prior art case, there are provided passages 23, 24, and a front insert 2 is provided being inserted into the passage 23 and a rear insert 5 is provided being inserted into the passage 24 and both the inserts 2, 5 are supported being fixed at two points, respectively, as described later. The front insert 2 is a hollow cylindrical member having a multiplicity of pair blowing holes 4a, 4b. The air blowing holes 4a are arranged in rows, having 15 holes each, extending linearly in a blade height direction, although not illustrated, and a hole diameter of each of them is 0.5 mm. Also, the air blowing holes 4b are arranged in a row, having 16 holes, extending linearly in the blade height direction and a hole diameter of each of them is 0.6 mm, which is slightly larger than that of the air blowing hole 4a. Within the passage 23, insert supporting portions 3a, 3b at two places are formed projecting from an inner wall of the passage 23. The front insert 2 is supported being fixed at two points by the insert supporting portions 3a, 3b of the two places with a predetermined space being maintained from an inner wall of the passage 23. The rear insert 5 is also a hollow cylindrical member having therearound a multiplicity of air blowing holes 7. The air blowing holes 7 are arranged in rows, having 20 holes each, extending linearly in the blade height direction on a dorsal side of the rear insert 5 and in two front rows, having 10 holes each, and in three rear rows, having 15 holes each, all extending linearly in the blade height direction on a ventral side of the rear insert 5 and a hole diameter of each of the air blowing holes 7 is 0.5 mm. The rear insert 5 is supported being fixed at front and rear two points, that is, a front portion of the rear insert 5 by an insert supporting portion 6a of a rib provided in the blade extending between a dorsal side and a ventral side thereof and a rear portion of the rear insert 5 by an insert supporting portion 6b provided projecting from the inner wall of the passage 24. A predetermined space is maintained between an inner wall of the passage 24 and the rear insert 5. In the projection 1 of the stationary blade 10, there are provided shower head cooling holes 11a in four rows of 1 ○ to 4 ○ extending linearly in the blade height direction, wherein the row has 21 holes, the row 2 ○ has 20 holes, the row 3 ○ has 21 holes and the row 4 ○ has 20 holes. A hole diameter of each of the shower head cooling holes 11a is 0.5 mm. Also, in a blade leading edge portion, in addition to the shower head cooling holes 11a, there are provided film cooling holes 11b, 11c in a respective row, having 19 holes each, extending linearly in the blade height direction and a hole diameter of each of the film cooling holes 11b, 11c is 0.5 mm. In a blade trailing edge portion also, there are provided film cooling holes 11d, 11e, wherein the film cooling holes 11d are in a row, having 19 holes, and the film cooling holes 11e are in row, having 20 holes each, all extending linearly in the blade height direction. Furthermore, in a blade dorsal portion, there are provided film cooling holes 12 in a row having 16 holes, wherein a hole diameter of each of the film cooling holes 12 is 0.6 mm. As compared with other cooling holes described above, said hole diameter of 0.6 mm is set slightly larger and instead said number of holes of 16 is set slightly smaller, so that outflow quantity of air through the film cooling holes 12 may not become excessive as compared with said other cooling holes. The film cooling holes 12 are positioned to correspond to an area W where air pressure is relatively low in the passage 23 or in the front insert 2. This area W is a place where dusts contained in the air are liable to stagnate and the film cooling holes 12 are holes through which the dusts are caused to flow out together with the air, as described later. In the first stage stationary blade constructed as mentioned above, the projection 1 has a curved surface formed to an elliptical curve on an ellipse long axis, as described later, and the shower head cooling holes 11a are provided in the four rows of 1 ○ to 4 ○ in the projection 1. While in the prior art case, there are provided shower head cooling holes in five rows in this portion, in the present invention, the projection 1 is provided in the portion where there is a large thermal stress and the projection 1 is formed having the elliptically curved surface, thereby the blade leading edge may be made smaller in size and the outflow of the air is improved as well, so that the number of the holes arranged there as well as the air quantity flowing there may be reduced. Also, in the prior art case, dusts contained in the air in the front insert 2 would stagnate in the area W where air pressure is comparatively low and come into the air blowing holes 4a, 4b in a dorsal portion of the front insert 2 and this may cause a clogging to thereby cause a cooling insufficiency, but in the present invention, the air blowing holes 4b in a dorsal side rear portion of the front insert 2 and the film cooling holes 12 of the blade 10 both near the area W are made to have their diameters larger than those of the other holes and dusts 50 contained in the cooling air flows into the space between the front insert 2 and the inner wall of the passage 23 through the air blowing holes 4b and further flows outside through the film cooling holes 12, as shown by broken lines. Thus , there occurs no clogging of the cooling air holes and the film cooling holes. Further, the front insert 2 is supported at two points by the two insert supporting portions 3a, 3b provided projecting from the inner wall of the blade 10 and the rear insert 5 is also supported at two points by the insert supporting portion 6a of the rib partitioning the passages 23, 24 and the insert supporting portion 6b provided projecting in the blade trailing edge portion, as described above. Thus, when the blade is assembled, the insertion into, and the positioning in, the passages 23, 24 of the inserts 2, 5 become facilitated and the assembling is simplified. Also, accuracy of the assembling is enhanced. Fig. 3 is a schematic view showing a shape of the blade leading edge portion of the above-mentioned embodiment, wherein Fig. 3 (a) shows the shape of the present invention and Fig. 3(b) shows that of the prior art. In Fig. 3(b), the blade leading edge has a curved surface of a circular shape 42, and while cooling air 34 which flows out of a blade interior flows along the curved surface of the blade leading edge, a portion of the cooling air 34 does not flow along the curved surface but becomes turbulent. But, in the blade of the present invention shown in Fig. 3(a), the blade leading edge has a curved surface of an elliptical shape 41, and cooling air 33 which flows out of the blade interior flows smoothly along the elliptically curved surface toward the blade dorsal portion, thus there is caused no turbulence of the air and the cooling effect can be enhanced. In Fig. 5, flow velocity of the cooling air according to positions of the blade is shown in comparison of the leading edge of the circular shape in the prior art and that of the elliptical shape of the present invention, wherein X shows the air flow velocity of the blade dorsal side and Y shows that of the blade ventral side, and also solid lines show a flow velocity pattern of the blade of the elliptical shape of the present invention and broken lines show that of the blade of the circular shape in the prior art. As shown there, on the blade dorsal side in the prior art case, there arises a velocity spike at the position shown by L where the air flow velocity varies and the cooling air does not flow smoothly, but in the elliptically curved leading edge of the present invention, there occurs no such velocity spike. Fig. 4 is a detailed view of the projection 1 of the blade leading edge shown in Fig. 1. The projection 1 has a curved surface of a circular shape or an elliptical shape, wherein the elliptical shape is more preferable, and in Fig. 4, the curved surface is formed to an elliptical curve on an ellipse 43 long axis. The projection 1 is formed to such elliptical curve, thereby the blade leading edge where there is a large thermal load can be made smaller in size, which results in being able to reduce the number of pieces of the. shower head cooling holes 11a as compared with the prior art case. That is, in the blade leading edge of the circular shape in the prior art, there are provided the shower head cooling holes in five rows, but in the present embodiment, the blade leading edge where the thermal load is large is made smaller and the shower head cooling holes may be provided in four rows. The projection 1 is provided projecting from a portion on the ventral side of the blade leading edge where the thermal load is large, as shown in Fig. 1, and thereby a high cooling effect can be obtained. As described above, in the gas turbine stationary blade of the present embodiment, (1) the front and rear inserts 2, 5 in the passages 23, 24 are supported at two points, respectively, and a structure to facilitate the assembling is realized, (2) the air blowing holes 4b of the front insert 2 and the film cooling holes 12 in the blade dorsal portion near the air blowing holes 4b, both having diameters larger than those of the other holes, are provided, the dusts in the air are caused to flow out and a clogging of the air blowing holes and the shower head or film cooling holes is prevented, (3) the blade leading edge is formed having the curved surface of an elliptical shape and the cooling air flow is made a smooth and non-turbulent flow, (4) the projection 1 is provided projecting from the blade leading edge, the blade leading edge where there is a large thermal load is made smaller and the number of rows of the shower head cooling holes 11a can be reduced, (5) the projection 1 is provided projecting from a portion on the ventral side of the blade leading edge and the cooling effect is enhanced. Thus, by all these improvements mentioned in (1) to (5) above, reliability of the gas turbine first stage stationary blade is enhanced remarkably. It is to be noted that the constructions mentioned in (1) to (5) above may be applied individually or in partial combination thereof, and if all of (1) to (5) above are applied, then the reliability of the stationary blade can be enhanced further. It is understood that the invention is not confined to the particular construction and arrangement of parts herein illustrated and described but embraces such modified forms thereof as come within the scope of the appended claims.

Claims: A gas turbine stationary blade constructed such that the blade (10) is provided with an outer shroud (21) and an inner shroud (22), a plurality of passages (23,24) provided in the blade (10) from a leading edge side to a trailing edge side of the blade (10), and a plurality of cooling air holes (11a-e,12) provided in the blade (10), wherein a cylindrical insert (2,5) is inserted into each of said passages (23,24) and fixed such that a predetermined space is maintained from an inner wall of the respective passage (23,24), wherein said cylindrical inserts (2,5) are respectively provided with a multiplicity of air blowing holes (4a,4b,7), wherein said air blowing holes (4a,4b) of the insert (2) in the leading edge side passage (23) comprise a first group of air blowing holes (4b) arranged in a blade height direction and a second group of air blowing holes (4a) arranged in a blade height direction, said first group of air blowing holes (4b) being arranged in a dorsal side rear portion of said insert (2) at the rear of the first group of air blowing holes (4a), wherein each air blowing hole (4b) of said first group has a diameter larger than that of each air blowing hole (4a) of said second group, wherein said cooling air holes (11a-e,12) comprise cooling air holes (12) provided in a dorsal portion of the blade (10) near said first group of air blowing holes (4b) such that air flowing.through the frist group of air blowing holes (4b) flows further out through said cooling air holes (12) in the dorsal portion of the blade (10), and wherein each of said cooling air holes (12) in the dorsal portion of the blade (10) has a diameter larger than that of other cooling air holes (11a-e) provided in the blade (10). A gas turbine stationary blade as claimed in claim 1, wherein said inserts (2,5) in each of said passages (23,24) are supported at two places (3a,3b,6a,6b). A gas turbine stationary blade as claimed in claim 1 or 2, wherein said air blowing holes (4a,4b) of said first group of air blowing holes (4b) and of said second group of air blowing holes (4a) of the insert (2) in the leading edge side passage (23) are arranged in rows extending linearly in the blade height direction. A gas turbine stationary blade blade as claimed in claim 1, 2 or 3, wherein a projection (1) is provided projecting from a portion of the leading edge of the blade (10), said projection (1) having a smoothly curved surface as well as a plurality of cooling air holes (11a) through which the cooling air is blown. A gas turbine stationary blade as claimed in claim 4, characterized in that said projection (1) has said curved surface formed to an elliptical curve on an ellipse (43) long axis. A gas turbine stationary blade as claimed in claim 4 or 5, characterized in that said leading edge of the blade (10) has a curved surface formed to an elliptical curve on an ellipse (41) long axis.

Inventors: ITO EISAKU, KUWABARA MASAMITSU, TOMITA YASUOKI, ITO, EISAKU, KUWABARA, MASAMITSU, TOMITA, YASUOKI, Ito, Eisaku, Takasago Research &amp; Development Cr., Kuwabara, Masamitsu, c/o Takasago Machinery Works, TOMITA, YASUOKI, C/O TAKASAGO MACHINERY WORKS
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI HEAVY INDUSTRIES, LTD.
Application year: 2000
Main classification: F01D5
IPC codes: F01D5