Paired stator vanes

BACKGROUND OF THE INVENTION:

Field of the Invention:

The present invention relates to a segmented gas turbine stationary blade unit according to the preamble portion of claim 1 in which two stationary blades are assembled in one shroud unit so as to reduce influence of thermal stress given on blade or shroud and to avoid occurrence of cracks.

Description of the Prior Art:

In gas turbine stationary blades, seal air leaks from inner side through gap between mutually adjacent inner shrouds to be discharged into combustion gas passage vainly, which results in increase of power burden of compressor. Recently, in order to lessen the gap which causes that leakage, trials are being done for making the stationary blades in a segmented form. In this case, plural stationary blades are fixed in one unit by shrouds, hence there occurs a large restraining force between the blades and this causes a local stress concentration due to thermal stress and cracks occur frequently.

Figs. 10(a) and (b) are perspective views respectively of a segmented stationary blade unit in the prior art and show state of occurrence of cracks at same time. In the figures, numeral 1a, 1b designates a stationary blade, numeral 22 designates an outer shroud and numeral 23 designates an inner shroud. Two stationary blades 1a, 1b are fixed in a shroud unit of the outer shroud 22 and the inner shroud 23 so as to form a segment.

When the stationary blades 1a, 1b are so constructed in one unit, the stationary blades 1a, 1b and the outer and inner shrouds 22, 23 are mutually restrained so that unreasonable force occurs due to thermal stress and cracks. are liable to occur in an inner side portion P3 of the stationary blade 1a and in a portion S1 of the inner shroud 23, as shown in Fig. 10 (a), and in both end portions P1, P2 of the stationary blade 1a and in a portion S2 of the inner shroud 23, as shown in Fig. 10(b).

In the gas turbine stationary blades, as mentioned above, in order to reduce leakage of the seal air, trials are being done for making the stationary blades segmented so as to lessen the gap between mutually adjacent inner shrouds. On the other hand, when the stationary blades are segmented, restraining force becomes larger, stress concentration occurs locally due to thermal stress and cracks occur frequently.

US-A-4 492 517 discloses a gas turbine stationary blade unit with the features of the preamble portion of claim 1.

US-A-4 015 910 discloses a gas turbine stationary blade unit where both the inner and the outer shrouds are divided and connected by flanges and bolts.

US-A-5 591 003 discloses a turbine nozzle support structure where only the outer shroud is divided into plural shroud segments. In this prior art a large number of stationary blades are attached to an integrated inner shroud and supported at the outer shroud in that the same is divided into a corresponding number of shroud segments that are connected by pins.

SUMMARY OF THE INVENTION:

It is the object of the present invention to provide a segmented gas turbine stationary blade unit comprising two stationary blades therein in which an outer shroud and an inner shroud are devised so as to mitigate a restraining force between the stationary blades in order to prevent stress concentration from occurring due to the thermal stress.

In order to attain that object the present invention provides a gas turbine stationary blade unit as defined in claim 1. A preferred embodiment is defined in dependent claim 2.

In the invention, the inner and outer shrouds are divided respectively and the divided and mutually adjacent shrouds are connected by the pins, having larger thermal expansion coefficient than the shrouds, inserted in the pinholes provided in the faces of divided portion and are jointed by bolts as fastening members via the flanges formed by the fitting plates being provided along the faces of divided portion and thus the jointed gas turbine stationary blade unit is constructed, hence, by virtue of the divided shrouds of the jointed blade unit, the rigidity of the shrouds is lowered and the temperature distribution is softened and the thermal stress at the blade end portions is mitigated. Further, by virtue of the jointed structure, relative movement between the mutually adjacent shrouds is prevented so that an integrated behavior therebetween is formed and a strong jointed blade unit is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS:

<ul id="ul0001" list-style="none" compact="compact"><li>Fig. 1 is a perspective view of a gas turbine stationary blade unit of a first example to explain certain features of the present invention.</li><li>Fig. 2 is a perspective view of a gas turbine stationary blade unit of a second example to explain certain features of the present invention.</li><li>Fig. 3 is a perspective view of the gas turbine stationary blade unit of the first example of Fig. 1 and shows state of bolt joint at a divided portion of outer shroud.</li><li>Fig. 4 is a cross sectional view taken on line A-A of Fig. 3.</li><li>Fig. 5 is a cross sectional view taken on line B-B of Fig. 3.</li><li>Fig. 6 is a view of life assessment of crack occurring portions in gas turbine second state stationary blade units in the prior art and the first and second examples, wherein Fig. 6(a) shows case of the prior art, Fig. 6(b) shows case of the second example and Fig. 6(c) shows case of the first example.</li><li>Fig. 7 is a perspective view of an assembly unit of gas turbine stationary blades of an embodiment according to the present invention.</li><li>Fig. 8 is an explanatory view showing one divided portion of the assembly unit of Fig. 7.</li><li>Fig. 9 is an explanatory view showing details of support pins, fitting plates, etc. in a flange portion of the assembly unit of Fig. 7.</li><li>Figs. 10(a) and (b) are perspective views respectively of a gas turbine stationary blade unit in the prior art and show state of occurrence of cracks at same time.</li></ul>

DESCRIPTION OF THE PREFERRED EMBODIMENTS:

Herebelow, description will be made concretely on examples according to the prior art and embodiments according to the present invention with reference to figures. Fig. 1 is a perspective view of a gas turbine stationary blade unit of a first example and, as shown there, an outer shroud and an inner shroud are constructed respectively to be divided at a central portion thereof and jointed together by bolts.

In Fig. 1, numeral 1a, 1b designates a stationary blade and numeral 2a, 2b designates a divided outer shroud, which fixes the stationary blade 1a, 1b, respectively. Numeral 3a, 3b designates a likewise divided inner shroud, which fixes the stationary blade 1a, 1b, respectively. The divided portion is a mid portion between the two stationary blades 1a, 1b, as shown in the figure, and there are provided flanges 4a, 4b (not shown) at the divided portions of the divided outer shrouds 2a, 2b, which flanges are jointed together by bolts. Likewise, at the divided portions of the divided inner shrouds 3a, 3b, there are provided flanges 5a, 5b (not shown), which are jointed together by bolts.

Fig. 2 is a perspective view of a gas turbine stationary blade unit of a second example. While in the first example, both the outer shroud and the inner shroud are divided, only the inner shroud is divided in the second example.

In Fig. 2, numeral 1a, 1b designates a stationary blade and numeral 12 designates an outer shroud, which, being not divided, fixes the stationary blade 1a, 1b, respectively. Numeral 13a, 13b designates a divided inner shroud and, like in Fig. 1, there are provided flanges 15a, 15b, which are jointed together by bolts.

Fig. 3 is a perspective view of the gas turbine stationary blade unit of the first example of Fig. 1 and shows state of bolt joint at the divided portion of the outer shroud.

In Fig. 3, flanges 4a, 4b are provided at divided end portions of the divided outer shrouds 2a, 2b, and boltholes 7 are bored therein so that both the flanges 4a, 4b are jointed together by bolts, that is, the divided portions are jointed together again by bolts.

With respect to the divided inner shrouds 3a, 3b also, although not shown, flanges 5a, 5b are provided at the divided portions, like in the divided outer shrouds 2a, 2b, and jointed together by bolts. By employing such a construction, while same function of a segmented blade as the prior art one is ensured, restraining force due to the thermal stress is mitigated and local stress concentration is prevented from occurring.

Fig. 4 is a cross sectional view taken on line A-A of Fig. 3. In Fig. 4, flanges 4a, 4b are provided to the divided outer shrouds 2a, 2b and boltholes 7 are bored in both of the flanges 4a, 4b so that the flanges 4a, 4b are jointed together by bolts and nuts 6.

Fig. 5 is a cross sectional view taken on line B-B of Fig. 3. In Fig. 5, flanges 5a, 5b are provided to the divided inner shrouds 3a, 3b so as to project therefrom toward an inner side thereof (toward a rotor side), and like in the divided outer shrouds 2a, 2b, boltholes 7 are bored and the flanges 5a, 5b are jointed together by bolts and nuts 6. Needless to mention, with respect to the divided inner shrouds 13a, 13b of the second example shown in Fig. 2 also, same flange construction is employed.

Fig. 6 is a view of life assessment of crack occurring portions in gas turbine second stage stationary blade units in the prior art and the first and second examples as described above, wherein Fig. 6 (a) shows case of the prior art shown in Fig. 10 where no shroud is divided, Fig. 6(b) shows case of the second example shown in Fig. 2 where only the inner shroud is divided and Fig. 6(c) shows case of the first examples shown in Fig. 1 where both the outer and inner shrouds are divided. In the figures, bar graphs are shown, wherein the crack occurring portions S1, S2, P1, P2 and P3 shown in Figs. 10(a) and (b) are taken on the horizontal axis and number of repetitions of stress is taken on the vertical axis. In Figs. 6(b) and (c), the number of repetitions of the stress of the second embodiment and the first embodiment, respectively, are shown in black bars and, in comparison thereof, the number of repetitions of the stress of the prior art one is shown in white bars with respect to each of the crack occurring portions, and magnifications of the black bars to the respective white bars are shown in parenthesis.

According to the life assessment of Fig. 6, in the case of Fig. 6(b) where the inner shroud only is divided, life endurance at S2 and P2 becomes 3.9 times and 5.7 times, respectively, of the prior art one and at P3 also, it becomes 8.1 times, hence it is found that the life up to the crack occurrence has elongated remarkably. Also, in the case of Fig. 6(c) where both the outer and inner shrouds are divided, likewise the life endurance becomes 3.9 times at S2, 6.7 times at P2 and 11.1 times at P3 and the life up to the crack occurrence has elongated more than the case where the one shroud only is. divided.

According to the first and second examples as described above, the stationary blade unit is constructed such that both the outer shroud and the inner shroud are divided or only the inner shroud is divided and flanges 4a, 4b and 5a, 5b or 15a, 15b are provided to the divided portions and are jointed together by the bolts and nuts 6, thereby same function as that of the segmented structure consisting of two stationary blades is maintained as it is and moreover frequency of crack occurrence due to the local stress concentration can be lessened greatly.

Next, an embodiment according to the present invention will be described with reference to Figs. 7 to 9. Fig. 7 is a perspective view of an assembly unit of gas turbine stationary blades of the embodiment, Fig. 8 is an explanatory view showing one divided portion of the assembly unit of Fig. 7 being divided into two parts and Fig. 9 is an explanatory view showing details of support pins, fitting plates, etc. in a flange portion of the assembly unit of Fig. 7.

In the present embodiment, like in the first example, an inner shroud 101 and an outer shroud 102 are divided into two parts, respectively, at a face of divided portion 109 which extends substantially in an axial direction of turbine, so that the assembly unit is divided into two shroud portions, that is, a portion jointing a stationary blade 103 and a portion jointing a stationary blade 104 which is adjacent to the stationary blade 103.

In the respective faces of divided portion 109 and at positions near both lengthwise ends thereof, pinholes 111 are bored extending in a tangential direction of turbine rotation, so that both pinholes 111 bored in the respective faces of divided portion 109 of the two shroud portions are connected to each other. Support pins 106 are inserted into the pinholes 111 to thereby connect the divided two shroud portions.

It is to be noted that the support pins 106 are made of hastelloy material of which thermal expansion coefficient corresponds to 16 to 20 × 10^-6/°C and the inner shroud 101 and the outer shroud 102 are made of nickel base heat resistant alloy of which thermal expansion coefficient corresponds to 12 to 16 × 10^-6/°C.

In the respective faces of divided portion 109 of the inner shroud 101 and the outer shroud 102 and on a side of operating gas flow of the pinholes 111, that is, on an outer side in a turbine radial direction of the pinholes 111 with respect to the inner shroud 101 and on an inner side in the turbine radial direction of the pinholes 111 with respect to the outer shroud 102, there are provided seal grooves 112 which connect to each other in the respective faces of divided portion 109 of the mutually adjacent shroud portions, and seal plates 108 are fitted in the seal grooves 112, thus sealing ability at the faces of divided portion 109 is ensured.

Further, at positions near lengthwise central portion of the respective faces of divided portion 109 of the inner shroud 101 and the outer shroud 102 and on an inner side in the turbine radial direction of the pinholes 111 with respect to the inner shroud 101 and on an outer side in the turbine radial direction of the pinholes 111 with respect to the outer shroud 102, reversely of the case of the seal grooves 112, fitting plates are fixed by welding 110 to form flanges 105 and the respective flanges 105 of the mutually adjacent shroud portions are jointed together by bolts 107 as fastening means.

That is, in the present embodiment, the inner shroud 101 is divided into the inner shroud 101 portion of the blade 103 and the inner shroud 101 portion of the blade 104, and the outer shroud 102 is divided into the outer shroud 102 portion of the blade 103 and the outer shroud 102 portion of the blade 104, and the inner shroud 101 portions respectively of the blade 103 and the blade 104 as well as the outer shroud 102 portions respectively of the blade 103 and the blade 104 are jointed by fitting the support pins 106 in the pinholes 111 in the faces of divided portion 109. Further, the flanges 105, fixed by welding on the inner and outer sides of the respective faces of divided portion 109, are jointed together by the bolts 107. Thus, a jointed blade unit consisting of the blade 103 and the blade 104 is constructed.

At blade end portions at which the blades 103, 104 are fitted to the inner and outer shrouds 101, 102, there acts thermal stress of the blades 103, 104 themselves and moreover there is a large influence given by thermal deformation of the inner and outer shrouds 101, 102 and this influence of the inner and outer shrouds 101, 102 is governed by rigidity of, and temperature distribution in, the inner and outer shrouds 101, 102.

In the present embodiment, however, the inner shroud 101 and the outer shroud 102 are divided, respectively, as mentioned above, hence the rigidity of the shrouds lowers, the temperature distribution becomes softened, deformation of the shrouds of warp or the like becomes smaller and forces acting on the blades become smaller, thereby alleviation of the thermal stress can be attained.

Also, between the respective faces of divided portion 109 of the inner shroud 101 and the outer shroud 102, there are provided the seal plates 108, which ensure the sealing between these faces. Further, in the respective faces of divided portion 109 of the inner shroud 101 and the outer shroud 102, there are bored the pinholes 111 and the support pins 106 which have larger thermal expansion coefficient than the shrouds are inserted therein, hence, due to difference in the thermal elongation between the material of the support pins 106 and the material of the shrouds in which the pinholes 111 are bored, there acts surface pressure between the support pins 106 and the pinholes 111, which prevents relative displacement between the support pins 106 and the shrouds so that an integrated behavior therebetween is formed, thus the burden of the bolts 107 which joint the flanges 105 is mitigated remarkably and soundness of this jointed blade unit is enhanced greatly.

The present invention has been described with respect to the embodiments as illustrated herein but the present invention is not limited thereto but may be added with various modifications in the concrete structure within the scope of the claims as set forth herebelow. For example, although in the third embodiment, both the inner shroud and the outer shroud are divided, only the inner shroud may be divided into two parts, like in the second embodiment.