EP2146051B1

EP2146051B1 - Rotor assembly for a gas turbine, gas turbine including said rotor assembly and method for cooling said rotor assembly

Info

Publication number: EP2146051B1
Application number: EP08425485A
Authority: EP
Inventors: Massimiliano Maritano
Original assignee: Ansaldo Energia SpA
Current assignee: Ansaldo Energia SpA
Priority date: 2008-07-17
Filing date: 2008-07-17
Publication date: 2011-09-07
Anticipated expiration: 2028-07-17
Also published as: EP2146051A1; ATE523658T1

Abstract

A rotor assembly (2) for a gas turbine (1) is provided with a rotor ring (3) extending about a longitudinal axis; a plurality of rotor blades (4) radially arranged about the rotor ring (3) and having an end portion (7) fixed to the rotor ring (3); and a plurality of sealing elements (30) arranged side-by-side in a circumferential direction, each of which is adapted to be coupled to the rotor ring (3) and to at least one blade (4) and is provided with an external face (32) adapted to be arranged in contact with a hot working fluid in the gas turbine (1) and with an internal face (33) adapted to be arranged in contact with a cooling fluid of the gas turbine (1); the blades (4) and the sealing elements (30) are shaped so as to form, when reciprocally coupled, at least one annular cooling channel (37) adapted to be traveled through by the cooling fluid.

Description

The present invention relates to a rotor assembly for a gas turbine, to a gas turbine including said rotor assembly and to a method for cooling said rotor assembly.
Gas turbines of known type generally include a rotating shaft, extending along a longitudinal axis, to which a plurality of rotor assemblies is connected. Each rotor assembly includes a rotor ring, a plurality of rotor blades and a plurality of sealing elements.
Each rotor ring is centered on the longitudinal axis and coupled to the plurality of rotor blades, which are radially arranged about the rotor ring. Specifically, each rotor ring is provided with a plurality of essentially equally spaced seats, which axially extend along the peripheral edge of the rotor ring. Each seat is adapted to be engaged by an end portion of a corresponding rotor blade by means of an axially sliding prismatic coupling. This type of coupling between the blade and the rotor ring ensures, when the turbine is running, an appropriate fastening of the blade in a radial direction, but allows the blade end portion to be displaced in the axial direction. Therefore, the axial movement of the end portions of the blades must be prevented. Such an object is generally reached by using sealing elements, which are circumferentially arranged side-by-side to essentially form a sealing ring and which are fixed to the rotor ring and to one or more rotor blades, on one or both of the annular faces of the rotor ring.
The sealing elements further contribute to correctly cool the rotor blades because they protect the end portions of the rotor blades from the hot working fluid in the gas turbine. Each sealing element indeed includes a wall having an external face in contact with the hot working fluid in the gas turbine and an internal face in contact with the cooling fluid of the gas turbine. A such type of rotor assembly is disclosed in US-A-4648799 , which describes a rotor assembly for a gas turbine including a plurality of side plates. Analogous rotor assemblies are described in documents US-A-1014577 , US-A-2008/0181767 and US-A-3010696 . However, the sealing elements are often subjected to overheating, because the contact with the cooling fluid along the internal face is not sufficient to ensure an adequate cooling of the whole sealing element. Specifically, the sealing element is provided with an upper edge adapted to be coupled to the rotor blade, which is particularly subject to overheating because it is subjected to a fairy high heat load due to its position close to the flow area of the hot working fluid. Such an upper edge reaches very high temperatures and undergoes plastic deformations due to the overheating and to the simultaneous action of the centrifugal force which cause a sort of welding of the sealing element onto the rotor blade. This implies great difficulties, for example, during the operations of disassembling the sealing elements, because very often it is necessary to resort to operations which damage the sealing elements and risk damaging the rotor blade as well.
It is an object of the present invention to make a rotor assembly which is free from the described drawbacks of the known art; specifically, it is an object of the invention to make a rotor assembly shaped so as to ensure an appropriate cooling of the upper edge of the cooling element.
In accordance with such objects, the present invention relates to a rotor assembly for a gas turbine according to claim 1.
It is a further object of the present invention to make an efficient gas turbine. In accordance with such objects, the present invention further relates to a gas turbine including at least one rotor assembly according to anyone of the claims from 1 to 9.
It is a further object of the present invention to provide a simple and effective method for cooling a rotor assembly of a gas turbine. In accordance with such objects, the present invention relates to a method for cooling a rotor assembly for a gas turbine according to claim 11.
Further features and advantages of the present invention will be apparent from the following description of a non-limitative embodiment thereof, with reference to the figures in the accompanying drawings, in which:

figure 1 is a perspective view, with parts in section and parts removed for clarity, of a first detail of the rotor assembly according to the present invention;
figure 2 is a perspective view, with parts in section and parts removed for clarity, of a second detail of the rotor assembly according to the present invention;
figure 3 is a perspective view, with parts in section and parts removed for clarity, of a third detail of the rotor assembly according to the present invention;
figure 4 is a section view, with parts removed for clarity, of a fourth detail of the rotor assembly according to the present invention;
figure 5 is a section view, with parts removed for clarity, of a fifth detail of the rotor assembly according to the present invention.

In figure 1, reference numeral 1 indicates a portion of a gas turbine including a rotor assembly 2 (only partially shown).
The rotor assembly 2 includes a rotor ring 3 (only partially shown), which is centered on a longitudinal axis (not shown in the accompanying figures) and is coupled to a plurality of rotor blades 4 (only two of which are shown for simplicity in the figure) arranged radially about the rotor ring 3.
The rotor ring 3 is provided with a plurality of essentially, equally spaced seats 5, which axially extend along a peripheral edge 6 of the rotor ring 3. Each seat 5 is adapted to be engaged by an end portion 7 of a corresponding rotor blade 4 by means of a sliding prismatic coupling; specifically, each seat 5 has two side walls 8 respectively provided with three axial undercuts 9 adapted to prevent the movement of the end portion 7 of the blade 4 in the radial direction when the turbine 1 is running.
Each blade 4 includes, as mentioned above, an end portion 7, a platform 11, integrally coupled to the end portion 7, and an elongated main body 12, which extends from the platform 11 on the opposite side with respect to the end portion 7.
The end portion 7 of each blade 4 may be inserted in the corresponding seat 5 of the rotor ring 3 in a direction parallel to the axis of the rotor ring 3. Specifically, the end portion 7 has a shape which is essentially complementary to the shape of the corresponding seat 5 of the rotor ring 3, but has a lower radial height than the radial height of the seat 5 so that, when the seat 5 is engaged, the end portion 7 forms a channel 14 for the passage of a cooling fluid, preferably air bled from the compressor (not shown) of the gas turbine 1.
The end portion 7 of each blade 4 is further provided with one or more internal channels (not shown in the accompanying figures), which face the channel 14 and provide to cool the end portion 7 itself and to feed a complex system of cooling channels 15 (only one of which is partially shown in figure 1) of the main body 12.
The main body 12 of each blade 4 includes a tip (not shown for simplicity in the accompanying figures), opposite to the end portion 7, a leading edge 16 and a trailing edge 17.
With reference to figures 1 and 2, the platform 11 of each blade 4 has two axially opposite peripheral portions 19, which axially exceed with respect to the end portion 7. A peripheral portion 19 of the platform 11 is provided, on the side facing the end portion 7, with a circumferential seat 20, which extends for the entire circumferential length of the platform 11.
A variant (not shown) of the present invention provides for both peripheral portions 19 having a seat 20, on the side facing the end portion 7.
With reference to figures 2 and 3, the seat 20 of each platform 11 has a bottom face 21, an external side face 22 and an internal side face 23, axially opposite to the external side face 22. Along the bottom face 21, the platform 11 is provided with a groove 24 extending in a circumferential direction of the entire circumferential length of the seat 20.
With reference to figures 3 and 4, along the internal side face 23 of the seat 20, the platform 11 includes two circumferentially spaced grooves 26, which lead into the groove 24. Along the external side face 22, the platform 11 includes a groove 27 which leads to the groove 24.
The grooves 26 and 17 are circumferentially offset to each other.
The rotor assembly 2 further includes a plurality of sealing elements 30 (only one of which is shown for simplicity in figure 1), which are adapted to be coupled to the rotor ring 3 and to the blades 4 and are arranged side-by-side in a circumferential direction to contribute to fasten, in the axial direction, the end portions 7 of the blades 4 and to correctly cool the end portions 7 of the blades 4. In the non-limitative example shown in the accompanying figures, the sealing elements 30 are arranged side-by-side in the circumferential direction on only one annular face of the rotor ring 3. A variant (not shown) of the present invention provides for the sealing elements 30 being arranged side-by-side in the circumferential direction on both annular faces of the rotor ring 3.
With reference to figures 1 and 2, each sealing element 30 includes an essentially rectangle-shaped wall 31, which has an external face 32 adapted to be arranged in use in contact with the hot working fluid in the turbine and an internal face 33 adapted to be arranged in use in contact with the cooling fluid from the channel 14.
With reference to figure 2, the wall 31 has an upper edge 34 adapted to engage the seat 20 of the platform 11 of at least one blade 4; in the example of the accompanying figures, the sealing element 30 is arranged straddled on two blades 4 and therefore the upper edge 34 engages the seat 20 of a blade 4 and the seat 20 of the adjacent blade 4.
Specifically, the upper edge 34 is adapted to engage the seat 20 of the platform 11 so that the external face 32 of the sealing element 30 is arranged essentially in abutment against the external side face 22 of the seat 20 of the platform 11 and so that the internal face 33 of the sealing element 30 is arranged essentially in abutment against the internal side face 23 of the seat 20.
The wall 31 has a lower edge 35 adapted to engage a corresponding portion of an annular housing 36 made in the rotor ring 3.
When coupled, the sealing elements 30 and the platforms 11 of the blades 4 of the rotor assembly 2 form: an annular cooling channel 37, which is essentially defined by the grooves 24 (see figures 3, 4, 5) of each platform 11 and by the upper edge 34 of each sealing element 30; a plurality of feeding channels 38, defined by the grooves 26 and by the internal faces 33 of the sealing elements 30; and a plurality of exhaust channels 39, defined by the grooves 27 and by the external faces 32 of the sealing elements 30.
In use, the cooling fluid from the channels 14 flowing into the space between the sealing elements 30 and the end portions 7 of the blades 4 is fed to the cooling channel 37 through the feeding channels 38, follows a given path inside the cooling channel 37 and is ejected by means of the exhaust channels 39 which lead into the areas in which the hot working fluid flows in the gas turbine 1.
The cooling fluid thus determines a cooling by convection of the area close to the upper edge 34 of the plurality of the sealing elements 30 during the passage inside the cooling channel 37 and a cooling by convection of the platforms 11 of the rotor blades 4 during the exit from the exhaust channels 39.
The present invention has the following advantages.
Firstly, in virtue of the particular shape of the rotor group 2 according to the present invention, the disassembly interventions on the rotor blades 4 are easier, faster and more cost-effective because the correct cooling of the upper edge 34 of the sealing elements 30 eliminates the problems related to plastic deformations of the upper edge 34.
Furthermore, in virtue of the rotor assembly 2 according to the present invention, it is possible to increase the operating temperature of the working fluid in the gas turbine 1 and, accordingly, increase the performance of the whole gas turbine 1.
Additionally, the production costs of the rotor assembly 2 may be reduced in virtue of the good cooling of the upper edge 34, reached by means of the particular shape of the rotor assembly 2, which no longer imposes the use of materials having high mechanical properties.
Furthermore, the risks of failure of the whole gas turbine 1 caused by the sealing elements 30 exiting from their seat due to thermal-mechanical deformation is minimized. This further determines an increase of the time span between a maintenance intervention and the next for the sealing elements 30.
Finally, the rotor assembly according to the present invention is adapted to be installed on any type of gas turbine, also on previously installed gas turbines.
It is finally apparent that changes and variations may be made to the rotor assembly, to the gas turbine and to the method described herein, without departing from the scope of the appended claims.

Claims

A rotor assembly for a gas turbine (1) including:
a rotor ring (3) extending about a longitudinal axis;

a plurality of rotor blades (4) radially arranged about the rotor ring (3) and having an end portion (7) fixed to the rotor ring (3), a platform (11), integrally coupled to the end portion (7), and an elongated main body (12), which extends from the platform (11) on the opposite side with respect to the end portion (7);

a plurality of sealing elements (30) arranged side-by-side in a circumferential direction, each of which is adapted to be coupled to the rotor ring (3) and to at least one blade (4) and is provided with an external face (32) adapted to be arranged in contact with a hot working fluid in the gas turbine (1), with an internal face (33) adapted to be arranged in contact with a cooling fluid of the gas turbine (1) and with an upper edge (34);

the blades (4) and the sealing elements (30) being shaped so as to form, when reciprocally coupled, at least one annular cooling channel (37) adapted to be traveled through by the cooling fluid; the platform (11) being adapted to be coupled to at least one corresponding sealing element (30);

the rotor assembly (2) being characterized in that the platforms (11) of the blades (4) and the upper edge (34) of the sealing elements (30) are shaped so as to form, when reciprocally coupled, the cooling channel (37).
A rotor assembly according to claim 1, characterized in that at least one of the plurality of platforms (11) of the blades (4) and the plurality of sealing elements (30) is provided with a groove (24) extending in a circumferential direction adapted to define the cooling channel (37).
A rotor assembly according to claim 2, characterized in that each platform (11) has two axially opposite peripheral portions (19), which axially exceed with respect to the end portion (7); at least one peripheral portion (19) being provided, on the side facing the end portion (7), with a circumferential seat (20) adapted to accommodate an upper edge (34) of at least one sealing element (22); the platform (11) being provided with the groove (24) along a face (21, 22, 23) of the seat (20).
A rotor assembly according to claim 3, characterized in that the platform (11) is provided with the groove (24) along a bottom face of the seat (20).
A rotor assembly according to anyone of the preceding claims, characterized in that the blades (4) and the sealing elements (30) are shaped so as to form, when reciprocally coupled, at least one feeding channel (38) of the cooling fluid, in communication with the cooling channel (37), and at least one exhaust channel (39) of the cooling fluid, in communication with the cooling channel (37).
A rotor assembly according to claim 5, characterized in that the feeding channel (38) and the exhaust channel (39) are circumferentially offset.
A rotor assembly according to claim 6, characterized in that the feeding channel (38) and the exhaust channel (39) are transversal to the cooling channel (37).
A rotor assembly according to claim 7, characterized in that at least one blade (4) is provided with at least a second groove (26) adapted to define a feeding channel (38) and at least another blade (4) is provided with at least a third groove (27) adapted to define the exhaust channel (39).
A rotor assembly according to claim 7 or 8, characterized in that each blade (4) is provided with at least a second groove (26) adapted to define a feeding channel (38) and at least a third groove (27) adapted to define the exhaust channel (39).
A gas turbine (1) including at least one rotor assembly (2) according to anyone of the preceding claims.
A method for cooling a rotor assembly (2) for a gas turbine (1); the rotor assembly (2) including a rotor ring (3); a plurality of rotor blades (4) arranged radially about the rotor ring (3) and having an end portion (7) fixed to the rotor ring (3), a platform (11), integrally coupled to the end portion (7), and an elongated main body (12), which extends from the platform (11) on the opposite side with respect to the end portion (7); a plurality of sealing elements (30) arranged side-by-side in a circumferential direction, each of which is coupled to the rotor ring (3) and to at least one blade (4), and is provided with an external face (32), adapted to be arranged in contact with a hot working fluid in the gas turbine (1), with an internal face (33), adapted to be arranged in contact with the cooling fluid of the gas turbine (1) and with an upper edge (34); the blades (4) and the sealing elements (30) being shaped so as to form, when reciprocally coupled, at least one annular cooling channel (37) adapted to be traveled through by the cooling fluid; the platform (11) being adapted to be coupled to at least one corresponding sealing element (30);
the method being characterized in that it includes the step of conveying the cooling fluid into an annular cooling channel (37) formed by coupling the platforms (11) of the blades (4) and the upper edge (34) of the sealing elements (30).