U.S. patent application number 12/012754 was filed with the patent office on 2008-09-04 for free-standing turbine blade.
Invention is credited to Armin de Lazzer, Matthias Neef, Norbert Surken.
Application Number | 20080213098 12/012754 |
Document ID | / |
Family ID | 38098571 |
Filed Date | 2008-09-04 |
United States Patent
Application |
20080213098 |
Kind Code |
A1 |
Neef; Matthias ; et
al. |
September 4, 2008 |
Free-standing turbine blade
Abstract
There is described a blade for a turbomachine, such as a steam
turbine. The blade has a blade tip, which is curved in relation to
the blade airfoil profile. The curvature has the shape of a
winglet, which is known from aircraft construction.
Inventors: |
Neef; Matthias; (Mulheim an
der Ruhr, DE) ; Surken; Norbert; (Mulheim a.d. Ruhr,
DE) ; Lazzer; Armin de; (Mulheim an der Ruhr,
DE) |
Correspondence
Address: |
SIEMENS CORPORATION;INTELLECTUAL PROPERTY DEPARTMENT
170 WOOD AVENUE SOUTH
ISELIN
NJ
08830
US
|
Family ID: |
38098571 |
Appl. No.: |
12/012754 |
Filed: |
February 5, 2008 |
Current U.S.
Class: |
416/223A ;
416/241R |
Current CPC
Class: |
Y02T 50/673 20130101;
F01D 5/20 20130101; Y02T 50/60 20130101; F04D 29/324 20130101; F04D
29/681 20130101 |
Class at
Publication: |
416/223.A ;
416/241.R |
International
Class: |
F01D 5/14 20060101
F01D005/14 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 5, 2007 |
EP |
07002465.8 |
Claims
1.-11. (canceled)
12. A blade for a turbomachine, comprising: a blade cross-sectional
profile with a pressure side and a suction side; and a blade tip
with a curvature.
13. The blade as claimed in claim 12, wherein the curvature is
formed as a bend.
14. The blade as claimed in claim 12, wherein the blade has a
length, and the curvature of the blade tip extends over 5% of the
length.
15. The blade as claimed in claim 12, wherein the blade tip is
curved towards the pressure side.
16. The blade as claimed in claim 12, wherein the blade tip is
curved towards the suction side.
17. The blade as claimed in claim 15, wherein the blade tip is
curved towards the suction side.
18. The blade as claimed in claim 12, wherein the blade tip, is
first curved towards the suction side and then curved towards the
pressure side in a radial direction towards the blade tip.
19. The blade as claimed in claim 12, wherein a edge of the blade
tip is formed basically parallel to a circumferential direction
which is formed during operation of the turbomachine.
20. The blade as claimed in claim 12, wherein the blade has
differently formed blade cross-sectional profiles along a radial
direction of the blade, and wherein a projection of the blade tip
in the radial direction is greater than a projection of the largest
blade cross-sectional profile, as seen in the radial direction.
21. The blade as claimed in claim 12, wherein the blade has
differently formed blade cross-sectional profiles along a radial
direction, and wherein a projection of the blade tip in the radial
direction is less than the projection of the largest blade
cross-sectional profile, as seen in the radial direction.
22. The blade as claimed in claim 12, wherein a blade tip surface
opposite to a casing inner wall of the turbomachine has a
wear-resistant coating.
23. The blade as claimed in claim 12, wherein the blade consists of
steel or consists of titanium.
24. The blade as claimed in claim 12, wherein a blade
cross-sectional profile of the blade tip reduces, as seen in the
radial direction.
25. A blade for a turbomachine, comprising: a winglet.
26. The blade as claimed in claim 25, wherein the blade has a
length, and the winglet of the blade extends over essentially 5% of
the length.
27. The blade as claimed in claim 25, wherein the winglet is curved
towards a pressure side of the blade, and wherein the winglet is
curved towards a suction side of the blade.
28. A low-pressure steam turbine, comprising: a blade with a
winglet.
29. The low-pressure steam turbine as claimed in claim 28, wherein
the blade has a length, and the winglet of the blade extends over
essentially 5% of the length.
30. The low-pressure steam turbine as claimed in claim 28, wherein
the winglet is curved towards a pressure side of the blade, and
wherein the winglet is curved towards a suction side of the
blade.
31. The low-pressure steam turbine as claimed in claim 28, wherein
the winglet is at least partly essentially parallel to a casing
inner wall of the low-pressure steam turbine and wherein the
winglet has a coating.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority of European Patent Office
application No. 07002465.8 EP filed Feb. 5, 2007, which is
incorporated by reference herein in its entirety.
FIELD OF INVENTION
[0002] The invention relates to a blade for a turbomachine, wherein
the blade is formed along a radial direction and has a blade tip
and also a blade profile with a pressure side and a suction
side.
BACKGROUND OF INVENTION
[0003] Free standing lowpressure blades are used in turbomachines,
such as in steam turbines, primarily in the low-pressure region.
For constructional reasons, such turbomachines have a comparatively
large radial gap between the blade tip and the casing. So that
losses, however, do not become too great, it is known to arrange
abrasive coatings on the blade tip or on the casing which lies
opposite the blade tip. With contact between the blade tip and the
casing, only the abrasive coating is slightly worn away, as a
result of which a comparatively small radial gap is created.
[0004] The leakage flow which flows through between the blade tip
and the casing is also referred to as gap jet. In low pressure
steam turbines, these gap jets cause pulsing flows in the diffuser,
which can lead to unwanted humming of the diffuser.
[0005] Furthermore, it is known to form the blades very thin in the
tip region, i.e. on the final millimeters of the blade end of the
blade geometry. The tip region then corresponds to the suction side
contour. By means of this measure, on one hand an aerodynamically
pronounced throttling effect of the gap flow is achieved, which
slightly reduces the gap loss, and on the other hand the radial
clearance can be designed smaller, since in the case of rubbing of
the blade tip with the casing the risk of damage can be considered
to be low because the tip region is worn away, as it were, on the
casing without major damage.
[0006] A further measure for reducing gap flows is achieved by the
use of blades with shrouds. The shrouds act as seals, as it were,
as a result of which the gap losses are reduced. However, such
blades with shrouds have mechanical disadvantages because the
shrouds represent comparatively large additional masses which lead
to an unwanted mechanical loading of the blades. A further
disadvantage which is brought about by the shrouds arises as a
result of interconnecting the blades via the shrouds. Such
connections can lead to additional vibrational and resonance modes
of the blade ring which is connected in this way.
SUMMARY OF INVENTION
[0007] It is an object of the invention to disclose a turbine blade
for a turbomachine, which can be used in a turbomachine and during
operation leads to low gap losses.
[0008] This object is achieved by means of a blade for a
turbomachine, wherein the blade is formed along a radial direction,
and has a blade tip and also a blade profile with a pressure side
and a suction side, wherein the blade tip has a curvature.
[0009] Therefore, the geometry of the blade is greatly altered by
the invention. Like in the case of the freely flow-washed wings of
an aircraft, the blade tip is formed with so-called winglets. With
this, an essential feature is that the blade tip has a sharp
curvature compared with the major part of the blade airfoil.
[0010] By this measure, the driving pressure difference across the
blade tip is reduced. A further effect is that the radial clearance
between the blade tip and the casing is reduced, and consequently
the gap loss becomes less. The efficiency of such a turbomachine is
ultimately improved.
[0011] Furthermore, the aerodynamic conditions in the region of the
blade tip can be better controlled, since aerodynamic shocks of the
flow around the profile are shielded against interaction with the
casing. As a result of this, shock reflexes are reduced.
[0012] A further effect of the blade according to the invention is
that the diffuser shows little inclination towards the so-called
diffuser humming.
[0013] Further advantageous development are disclosed in the
dependent claims.
[0014] The curvature is preferably formed as a bend. Therefore, the
blade tip is formed in the manner of a winglet which is known from
aircraft construction.
[0015] So, it is advantageous if the blade tip, as seen in the
radial direction in the direction of the blade tip, is formed in a
manner in which it is first curved towards the suction side and
then curved towards the pressure side.
[0016] As a result of this, the centrifugal force which acts upon
the blade tip is minimized, as it were, in an optimum manner
because the centrifugal force acts on the one hand upon one side
(suction side) of the extension direction of the blade and on the
other hand upon the other side (pressure side) of the extension
direction of the blade.
[0017] In a further advantageous development, a wear-resistant
coating is applied to the blade tip surface which during operation
lies opposite a casing inner wall. As a result of this, contacts
which occur during operation between the blade tip and the blade
inner casing can be tolerated. The coating has such strength that
damage to the blade inner casing hardly occurs. An exemplary
embodiment of the invention is subsequently explained in more
detail with reference to drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] In the drawings:
[0019] FIG. 1 shows a perspective view of a turbine blade according
to the invention,
[0020] FIG. 2 shows a sectional view of the turbine blade, as seen
from above, in two different elevations,
[0021] FIGS. 3, 4, 5, 6 show a sectional view along the line A-A
from FIG. 2 for different embodiments of the turbine blade tip,
[0022] FIG. 7 shows pressure characteristic on the turbine blade
tip.
DETAILED DESCRIPTION OF INVENTION
[0023] In FIG. 1, a turbine blade 1 is to be seen in perspective
view. The turbine blade has a blade root 2 which is suitable for
fastening in a rotor, which is not shown. In this case, the blade
root has a so-called fir-tree root shape. Further embodiments for
the blade root 2 are known, such as the hook-type root embodiment
or T-shaped root embodiment. Such turbine blades 1 can be used in
turbomachines such as steam turbines, gas turbines or compressors.
The turbine blade 1 is formed along a radial direction 3 and has a
blade tip 4 and also a blade profile with a pressure side 6 and a
suction side 7.
[0024] The blade tip 4 of the turbine blade 1 has a curvature 8.
The curvature 8 in this case is localized on the upper region of
the blade tip 4. The curvature 8 is formed as a bend, as a result
of which the blade tip is formed in the manner of a winglet, which
is known from aircraft construction. The blade 1 has an overall
length L which can be calculated from the surface of the blade root
9 to the blade tip 4. The curvature 8 occurs in a region of
basically about 5% of the overall length L, calculated from the
blade end point 10.
[0025] As shown in FIGS. 3, 4, 5 and 6, the blade tip 4 can be
formed in different ways. For clarity, a rotational direction
.omega. is indicated in FIGS. 3, 4, 5 and 6 respectively.
Furthermore, in FIGS. 3, 4, 5 and 6 the inner casing 11, which lies
opposite the blade tip 4, was shown. In one embodiment, the blade
tip 4 can be curved towards the pressure side 6. In an alternative
embodiment, the blade tip 4 can be curved towards the suction side
7.
[0026] In a further embodiment, the blade tip 4, as seen in the
radial direction 3 in the direction of the blade tip 4, is formed
in a manner in which it is first curved towards the suction side 7
and then curved towards the pressure side 6.
[0027] The blade tip 4 has a blade tip edge 12 which is formed
basically parallel to a circumferential direction which is formed
during operation.
[0028] The blade 1 has differently formed blade cross-sectional
profiles 5 along the radial direction 3. In one embodiment, the
projection of the blade tip 4, as seen in the radial direction 3,
is smaller than the projection of the largest blade cross-sectional
profile 5 in the radial direction 3. In other words, the blade tip
edge 12 does not project beyond the largest blade cross-sectional
profile 5.
[0029] The blade has a blade tip surface 13 which, during
operation, lies opposite a casing inner wall 11 and which is
provided with a wear-resistant coating. This wear-resistant
coating, as shown in the example according to FIG. 4, can have a
serrated surface. This wear-resistant coating, for example, may
have been applied by means of surface layer welding.
[0030] The blade 1 can be produced from steel or from titanium. The
blade cross-sectional profiles 5 reduce in the direction of the
radial direction 3. As is to be seen in the examples in FIG. 5 and
FIG. 6, the blade tip 4 can taper to a point or taper in wedge-form
in the direction of the blade tip edge 12.
[0031] The curved turbine blade tips 4 are preferably used in
low-pressure last stage blades in low-pressure steam turbines. The
circumferential speed of the blade tip 4 in this case can be at
values of more than Mach 1. As a result of this, use in the
aerodynamic range of transonic flows is possible, In this case,
both the inflow and the outflow are to be understood as transonic
flow.
[0032] In FIG. 2, a plan view of the turbine blade 1 from above is
to be seen.
[0033] In FIG. 7 is shown how the pressure distribution behaves
with a curved turbine blade tip 4 and without a curved turbine
blade tip.
[0034] The curvature 8 preferably occurs on the pressure side 6 of
the blade 1 in order to reduce gap flow losses.
[0035] The curvature 8 is designed in such a way that the blade end
point 10 does not axially project beyond the axial width of the
blade cross-sectional profile 5. The curvature 8 of the blade tip
4, in order to minimize further gap losses, follows a conicity of
the casing.
[0036] According to FIG. 3 and FIG. 4, the blade tip 4 is formed in
the shape of a book. In this embodiment of the blade tip 4, the
centrifugal force which is induced in the curvature acts in a
radial direction of the turbine blade 1.
[0037] For further improvement of the gap losses, a coating 14 can
be applied to the blade tip surface. This coating 14 can be formed
as an abrasive wear coating, with which a contact with the inner
casing does not lead to major damage.
[0038] The curvature 8 of the turbine blade tip 4 can be produced
by means of close-tolerance finish forging. The curvature 8 can
also be produced by means of envelope forging with subsequent
milling of the blade airfoil.
* * * * *