EP1873355A1

EP1873355A1 - Turbine rotor blade

Info

Publication number: EP1873355A1
Application number: EP06013266A
Authority: EP
Inventors: Robert Howell
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2006-06-27
Filing date: 2006-06-27
Publication date: 2008-01-02

Abstract

A turbine rotor blade (3) is provided. The turbine rotor blade (3) has a root end (5) by which it can be fixed to a turbine rotor hub (7), and a tip end (9) remote from the root end (5) which carries a shroud segment (11). The rotor blade (3) is adapted to form a blade ring together with further rotor blades (3) fixed to the rotor hub (7), whereby the shroud segments (11) of the blade rings' rotor blades (3) together form a shroud ring which circumferentially surrounds the rotor hub (7). The shroud segment (11) comprises a projection (17) so as to allow for overlapping the shroud segment (11) of a neighbouring rotor blade in the blade ring in circumferential direction of the rotor hub (7).

Description

The present invention relates to a turbine blade, in particular to a gas turbine blade having a shroud at its tip end.
In a gas turbine engine, a fuel is burned in a burner assembly to produce hot pressurized exhaust gases which are then fed to a turbine stage where they, while expending and cooling, transfer momentum to turbine blades of a rotor thereby imposing rotational movement on the rotor. A usual turbine stage comprises alternating cascades of turbine blades fixed to and rotating with the rotor and stationary turbine vanes. A cascade of turbine blades is formed by a blade ring with a number of turbine blades spread regularly around the circumference of the rotor.
The efficiency of the gas turbine engine depends on the efficiency of transforming momentum from the expanding and cooling exhaust gases to the turbine blades. In order to keep the fraction of exhaust gases which transfer momentum to the turbine rotor as high as possible, it is common practise to provide the blade tip with a tip shroud which forms a segment of a circumferential ring around the outer ends of the blades. An example of a rotor with shrouded rotor blades is, e.g., shown in US 5,211,540 .
It is desirable to have minimum tolerances between the shroud and the casing of the turbine stage in order to minimise leakage of hot exhaust gases, i.e. hot exhaust gases bypassing the shrouded blade cascade through the tolerances. Leaking exhaust gas would lead to a loss of usable momentum of the exhaust gas, which in turn would reduce the efficiency of the gas turbine stage.
Shroud curl occurs when the shroud of the blade has been exposed to hot gases over a longer period of time, hence during operation in the load range. Curl is caused by creep in the material leading to plastic deformation. The purpose of the shroud is twofold. Besides preventing leakage over the blade tip and improving the efficiency of the turbine, it also improves the dynamic/vibration qualities of the blade. Depending on the shape of the contact surface between the shroud vibrations e.g. dynamic movements can be prevented or damped out. Furthermore due to the contact between the shrouds the Eigen frequencies of the individual blades are increase compared to if they are moving freely. During barrelling and start-up the shrouds may not be in full contact. However, when the centrifugal force is applied to the blade it will somewhat straighten out the initial twist/stagger of the airfoil over the height of the blade ("untwist"). Doing so contact forces are applied between the blades in the shroud region. If curl occurs the contact may be lost and the blade can be transferred to a operating regime where high cycle fatigue is activated and eventually leading to blade failure. A shortened service life of the shrouded blades can be the consequence.
It is therefore an objective of the present invention to provide a turbine rotor blade with a shroud segment which reduces the propensity of curling in the shroud.
It is a further objective of the invention to provide an improved turbine rotor by which the leakage can be reduced.
These objects are solved by a turbine rotor blade, as claimed in claim 1, and by a turbine rotor, as claimed in claim 6, respectively.
An inventive turbine rotor blade has a root end by which it can be fixed to a turbine rotor hub and a tip end remote from the root end which carries a shroud segment. The rotor blade is adapted to form a blade ring together with further rotor blades fixed to the rotor hub. The shroud segments of the blade ring's rotor blades together form a shroud ring which circumferentially surrounds the rotor hub. In the inventive turbine rotor blade the shroud segment comprises a projection so as to allow for overlapping the shroud segment of a neighbouring rotor blade in the blade ring in circumferential direction of the rotor.
By such an overlapping, it can be achieved that neighbouring shrouds are interlocked. This redistributes the load of the shroud between the blades and thereby preventing the curl.
In an implementation of the overlapping which is particularly advantageous, the shroud has a short side and a long side in circumferential direction with respect to the rotor. The projection is formed in the long side so as to allow for overlapping the short side of a neighbouring rotor blade's shroud segment on the short side's radial inner side. Since the long side is more flexible than the short side, a curl would occur on the long side rather than on the short side. When the long side is located radial inwards with respect to the short side in the overlapping zone, the less flexible short side prevents the long side from curling outwards.
The overlapping can be realized by giving the shroud's end faces in circumferential direction contours which are inverse to each other, e.g. stepped, sloped or teethed contours.
If one or more fins extend radial outwards from the shroud, the contours of the end faces can be continued through the fin's circumferential end faces.
An inventive turbine rotor comprises a rotor hub and at least one blade ring having a number of inventive turbine blades fixed to the rotor hub. The shroud segments of the rotor blades form a shroud ring. With such a rotor, tolerances between the outer circumference of the shroud ring and the inner wall of the turbine stage's casing can be kept small as curling outwards of the shrouds can be reduced. In turn, the leakage of hot pressurised exhaust gases through the blade ring can be reduced.
Further features, properties and advantages of the invention will become clear from the following description of embodiments in conjunction with the accompanying drawings.
Figure 1 shows a first embodiment of the inventive turbine rotor blade in a view onto the rotor blade's leading edge.
Figure 2 shows the rotor blades shown in Figure 1 seen from radially outwards.
Figure 3 shows a second embodiment of the inventive turbine rotor blade.
Figure 4 shows a third embodiment of the inventive turbine rotor blade.
Figure 5 shows a fourth embodiment of the inventive turbine rotor blade.
Figure 6 shows a fifth embodiment of the inventive turbine rotor blade.
Figure 1 shows a section of a blade ring 1 comprising a number of inventive turbine blades 3. Each turbine blade 3 has a root end 5 by which it is fixed to a rotor hub 7. The rotor hub 7 and the blade rings fixed thereto form a rotor for a gas turbine engine. Remote from the root end 5 the turbine blade 3 comprises a tip end 9, to which a shroud segment 11 is fixed. The shroud segments 11 of the blade ring's turbine blades 3 form a shroud ring which extends circumferentially around the rotor hub 7.
The circumferential end faces 15 and 17 of each shroud segment 11 are sloped with respect to the radial direction of the rotor. By the slope, an overlapping region 19 between neighbouring shroud segments 11 is formed. Each shroud segment has, in circumferential direction, a long side 21 and a short side 23. The slope is such that the long side 21 overlaps the short side of a neighbouring shroud segment 11 radially inwards. The short side 23 then prevents the more flexible long side 21 from curling outwards, e.g. in a transition mode of the gas turbine engine of which the rotor is a part.
From each shroud segment 11 a fin 13 extends radially outwards. The slope in the shroud segment's end faces 15, 17 is continued in the circumferential end faces 25, 27 of the fins 13.
A second embodiment of the inventive turbine rotor blade 3 is shown in Figure 3. The second embodiment differs from the first embodiment in that the circumferential end faces 15, 17 of the shroud segment 11 and the circumferential end faces 25, 27 of the fin 13 are not sloped, but stepped.
A third embodiment of the inventive turbine rotor blade is shown in Figure 4. This embodiment differs from the embodiment shown in Figure 1 in that the end faces 15, 17 of the shroud segment 11 and the end faces 25, 27 of the fin 13 have a dove tail structure at the long side 21 and a spike structure at the short side which is inverse to the dove tail structure of the long side 21.
Figure 5 shows a fourth embodiment of the inventive turbine rotor blade 3. The fourth embodiment differs from the first embodiment in that the end faces 15, 17 of the shroud segment 11 and the end faces 25, 27 of the fin 13 are teethed. The teething at the short side's end faces 15, 25 is inverse to the teething at the long side's end faces 17, 27.
A fifth embodiment of the inventive turbine rotor blade 3 is shown in Figure 6. The fifth embodiment differs from the first embodiment in that the circumferential end faces 15, 17 of the shroud segment 11 and the circumferential end phases 25, 27 of the fin 13 show a Z-notch structure.
Except for the differences explained with respect to Figures 3 to 6, the second to fifth embodiment do not differ from the first embodiment, as it was described with respect to Figures 1 and 2.
Although the overlapping structures are present in the end faces of the shroud segments 11 and in the end faces of the fins 13 throughout the embodiments, the overlapping structures could be confined to the end faces of the shroud segments 11. In this case the dove tail and the spike of the third embodiment, or the Z-notch structure of the fifth embodiment would be located completely in the end faces 15 and 17 of the shroud segment 11.
With the inventive turbine rotor blade, the curling of the shroud can be reduced compared to state of the art shrouds.

Claims

A turbine rotor blade (3) having a root end (5) by which it can be fixed to a turbine rotor hub (7), and a tip end (9) remote from the root end (5) which carries a shroud segment (11), the rotor blade (3) being adapted to form a blade ring together with further rotor blades (3) fixed to the rotor hub (7), whereby the shroud segments (11) of the blade rings' rotor blades (3) together form a shroud ring which circumferentially surrounds the rotor hub (7), characterised in that the shroud segment (11) comprises a projection (17) so as to allow for overlapping the shroud segment (11) of a neighbouring rotor blade in the blade ring in circumferential direction of the rotor hub (7).
The turbine rotor blade (3) as claimed in claim 1, characterised in that the shroud (11) has a short side (23) and a long side (21) in the circumferential direction and in that the projection (17) is formed in the long side (21) so as to allow for overlapping the short side (23) of a neighbouring rotor blade's shroud segment (11) on the short side's (23) radial inner side.
The turbine rotor blade (3) as claimed in claim 1 or claim 2, characterised in that the contours of the shroud's end faces (15, 17) in circumferential direction are inverse to each other.
The turbine rotor blade (3) as claimed in claim 3, characterised in that the end faces (15, 17) are stepped, sloped, or teethed.
The turbine rotor blade (3) as claimed in claim 3 or claim 4, characterised in that at least one fin (13) extends radially outwards from the shroud (11) and in that the contours continue through the fin's (13) circumferential end faces (25, 27).
A turbine rotor with a rotor hub (7) carrying at least one blade ring having a number of turbine blades (3) according to any of the preceding claims, the shroud segments (11) of the turbine blades (3) forming a shroud ring.