U.S. patent application number 12/929047 was filed with the patent office on 2011-07-07 for stator blade for a turbomachine, especially a stream turbine.
This patent application is currently assigned to ALSTOM Technology Ltd. Invention is credited to Ralf Greim, Said Havakechian, Mourad Lakehel, Carsten Mumm.
Application Number | 20110164970 12/929047 |
Document ID | / |
Family ID | 38055104 |
Filed Date | 2011-07-07 |
United States Patent
Application |
20110164970 |
Kind Code |
A1 |
Greim; Ralf ; et
al. |
July 7, 2011 |
Stator blade for a turbomachine, especially a stream turbine
Abstract
The invention relates to a stator blade (4) of a turbomachine,
especially of a steam turbine, which has the following geometric
features. A lean curvature, a swept curvature, a twist in the
radial direction of the respective blade (4), a hub-side
circumferential step (14) which in the direction of flow (15) falls
away inwards and radially to the rotational axis (8) of the
turbomachine, a chord length (s) of the blade which varies over the
radial extent of the stator blade (4), and also a cross-sectional
profile of the blade (4) which varies over the radial extent of the
stator blade (4).
Inventors: |
Greim; Ralf; (Birmenstorf,
CH) ; Havakechian; Said; (Baden, CH) ;
Lakehel; Mourad; (Zuerich, CH) ; Mumm; Carsten;
(Waldshut-Tiengen, DE) |
Assignee: |
ALSTOM Technology Ltd
Baden
CH
|
Family ID: |
38055104 |
Appl. No.: |
12/929047 |
Filed: |
December 23, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12241825 |
Sep 30, 2008 |
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12929047 |
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PCT/EP2007/052828 |
Mar 23, 2007 |
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12241825 |
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Current U.S.
Class: |
415/208.1 |
Current CPC
Class: |
F05D 2250/71 20130101;
F01D 5/141 20130101; F05D 2240/301 20130101; F05D 2250/20 20130101;
F05D 2220/72 20130101; F01D 9/041 20130101 |
Class at
Publication: |
415/208.1 |
International
Class: |
F01D 9/02 20060101
F01D009/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 31, 2006 |
DE |
102006015532.7 |
Claims
1. A stator blade for a turbomachine, especially for a steam
turbine, characterized by the following geometric features: a lean
curvature perpendicular to the blade chord, essentially in the
circumferential direction, a sweep curvature parallel to the blade
chord, essentially in the axial direction of the turbomachine, a
twist in the radial direction of the respective blade, a hub-side
circumferential step, which in the direction of flow falls away
inwards and radially to the rotational axis of the turbomachine, a
chord length of the blade which varies over the radial extent of
the stator blade, a cross-sectional profile of the blade which
varies over the radial extent of the stator blade.
2. The stator blade as claimed in claim 1, wherein the lean
curvature varies along the radial blade length, and/or the lean
curvature decreases along the radial blade length from the hub to
the casing, and/or a curvature angle (.gamma.) between a tangent
which lies against the blade surface at a trailing edge or at a
leading edge of the stator blade, and a radial line which extends
orthogonally to the rotational axis of the turbomachine, lies
within a range of 0.degree..ltoreq..gamma..ltoreq.15.degree.,
and/or the stator blade has a positive lean curvature in the
direction of rotation.
3. The stator blade as claimed in claim 1, wherein the sweep
curvature of the stator blade varies along the radial blade length,
and/or the sweep curvature of the stator blade along the radial
blade length has a positive value in the region of the hub and has
a negative value in the region of the casing, and/or a curvature
angle between a meridional tangent which lies against the blade
surface at a leading edge or at a trailing edge, and a radial line
which extends orthogonally to the rotational axis of the
turbomachine, lies within a range of
15.degree..ltoreq..delta..ltoreq.-20.degree..
4. The stator blade as claimed in claim 1, wherein a metal angle at
the trailing edge is defined between a circumferential line in the
circumferential direction of the turbomachine and a tangent to the
curvature center line at the trailing edge, and/or the metal angle
varies along the radial blade length, and/or the metal angle is
larger at the hub than in the region of the casing, and/or the
metal angle between a tangent to the curvature center line at the
trailing edge of the stator blade and the rotational axis of the
turbomachine lies with a range of
25.degree..ltoreq..alpha..sub.2.ltoreq.10.degree..
5. The stator blade as claimed in claim 1, wherein the hub-side
circumferential step has an S-shaped profile between a leading edge
and a trailing edge of the stator blade or extends linearly between
the two edges, and/or the leading edge and the trailing edge do not
extend in a parallel manner, and/or an angle between a tangent to
the circumferential step and the rotational axis of the
turbomachine lies within a range of
-20.degree..ltoreq..beta..ltoreq.20.degree..
6. The stator blade as claimed in claim 1, wherein a pitch ratio,
that is to say a quotient of a blade spacing between adjacent
stator blades in the circumferential direction and a chord length
varies over the radial extent of the stator blade, and/or the pitch
ratio at the hub is smaller than in the region of the casing,
and/or the pitch ratio lies within a range of
0.45.ltoreq.t/s.ltoreq.0.75.
7. The stator blade as claimed in claim 1, wherein an inflow-side
incidence angle of the curvature center line varies over the radial
blade length of the stator blade, and/or the inflow-side incidence
angle of the curvature center line is smaller at the hub than in
the region of the casing, and/or the inflow-side incidence angle of
the curvature center line lies within a range of
55.degree..ltoreq..alpha..sub.1.ltoreq.110.degree..
8. The stator blade as claimed in claim 1, wherein a wedge angle
between a surface tangent to a pressure side and a surface tangent
to a suction side at a trailing edge of the stator blade varies
over the radial blade length of the stator blade, and/or the wedge
angle is larger at the hub than in the region of the casing, and/or
the wedge angle lies within a range of
15.degree..ltoreq.WE.ltoreq.0.degree..
9. The stator blade as claimed in claim 1, wherein a narrowest flow
cross section between adjacent stator blades shifts from the hub
towards the casing against the direction of flow.
Description
TECHNICAL FIELD
[0001] The present invention relates to a stator blade for a
turbomachine, especially for a steam turbine with at least one
stator blade row.
BACKGROUND OF THE INVENTION
[0002] Curved blades are used especially in steam construction as
an embodiment of turbine blades particularly when strong
three-dimensional flows occur, which feature pronounced radial
differences in the static pressure variation between rotor side and
stator side, and which arise as a result of the deflection in the
stator blades. The flow of a flow medium in a last stage of a
low-pressure turbine with large inflow cross section leads to a
radial reaction distribution which acts negatively upon the
efficiency of the steam turbine, especially in the case of a large
ratio between blade length and hub. The reaction distribution in
this case is different in the radial direction, wherein the
reaction distribution is low at the hub and high in the region of a
casing of the turbine, which is generally regarded as being
disadvantageous.
[0003] A high reaction in the hub region reduces the gap losses in
the stator blade ring and therefore leads to improved efficiency.
In order to optimize the radial reaction distribution, curved
stator blades are therefore used.
[0004] A turbine with stator blades which are curved only in the
circumferential direction is known from DE 37 43 738 A1, the blade
curvature of which is directed over the height of the blade towards
the pressure side of the adjacent stator blade in the
circumferential direction in each case. Blades, the curvature of
which is directed over the height of the blade towards the pressure
side of the adjacent stator blade in the circumferential direction
in each case, are additionally known from the aforesaid
publication. Consequently, boundary layer pressure gradients which
extend both radially and in the circumferential direction are to be
reduced in an effective manner and as a result the aerodynamic
blade losses are altogether reduced.
[0005] Turbines with stator blades which are curved in the axial
direction and in the circumferential direction are known for
example from DE 42 28 879 A1. Upstream of a rotor cascade, in this
case a fixed stator cascade is arranged, the rotor blades of which
are fluidically optimized for full load with regard to number and
also with regard to their chord-to-pitch ratio. The stator blades
impart to the flow the swirl which is necessary for entry into the
rotor cascade. The curvature of the blades extends perpendicularly
to the chord, which is achieved as a result of displacement of the
profile cross section both in the circumferential direction and in
the axial direction. The curvature of the stator blades is directed
towards the pressure side of the adjacent stator blade in the
circumferential direction in each case. As a result of this
curvature perpendicularly to the blade chord, the blade surface
which is projected in the radial direction is greater than in the
case of a known curvature only in the circumferential direction, as
a result of which the radial force upon a flow medium is increased
so that the flow medium is pressed onto a passage wall and reduces
the boundary layer thickness there.
[0006] A turbine blade is known from WO 2005/005784 A1, which in
the direction of flow is negatively swept on its rotor-side end and
on its stator-side end, and in a direction which is radial with
regard to the direction of flow is inclined towards the pressure
side on its rotor-side end and also on its stator-side end. In this
case, therefore, it concerns a turbine with turbine blades which
are curved both in the circumferential direction and in the axial
direction.
[0007] A final stage of a turbine which is exposed to axial
throughflow, with a large passage divergence and also with a row of
curved stator blades and a row of tapered and twisted rotor blades
is known from EP 0 916 812 B1, wherein the stator blades in the
axial direction are positively swept on their rotor-side end and
negatively swept on their stator-side end, in each case with regard
to the run of the rotor-side passage boundary. The positive sweep
of the stator blade in this case extends over two thirds of the
height of the blade and then merges into the negative sweep,
wherein in the region of positive sweep the stator blade trailing
edge extends parallel to the stator blade leading edge, and in the
region of negative sweep an axial diffuser, which continuously
widens towards the wall, is formed between stator blade and rotor
blade with increasing deceleration of the axial component of the
flow medium.
[0008] Further turbines with turbine blades which are curved in the
circumferential direction and/or in the radial direction are known
for example from U.S. Pat. No. 5,249,922, from U.S. Pat. No.
4,470,755, from U.S. Pat. No. 4,500,256 or from EP 0 425 889
A1.
SUMMARY OF THE INVENTION
[0009] It is the object of the present invention to provide a
stator blade for a turbomachine, which by reducing the aerodynamic
blade losses enables an improved efficiency of the turbomachine to
be achieved.
[0010] This problem is solved by means of the subject of the
independent claim. Preferred embodiments are the subject of the
dependent claims.
[0011] The invention is based on the general idea in the case of a
turbomachine of providing at least the stator blades of a stator
blade row with a lean curvature, a sweep curvature, a twist, a
chord length which varies over the radial extent of the stator
blade, and a cross-sectional profile which varies over the radial
extent of the stator blade. In addition, the stator blade row has a
hub-side circumferential step which in the direction of flow falls
away inwards and radially to the rotational axis of the
turbomachine. As a result of this, a number of advantages can be
combined. On the one hand, a radial distribution of a mass flow
which flows through the turbine and also a radial pressure gradient
are reduced, while on the other hand a greater mass flow, that is
to say, throughflow volume, is induced in the region of the hub. At
the same time, the impingement energy of water droplets is reduced,
as a result of which the erosion behavior is favorably influenced.
In particular, the reduced impingement energy can be used for
reducing the reaction degree at the blade tip, as a result of which
lower absolute velocities can be realized on a stator-blade
trailing edge so that lower leakage losses are encountered.
[0012] Further important features and advantages of the stator
blade according to the invention for a turbomachine result from the
dependent claims, from the drawings and from the associated figure
description with reference to the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Preferred embodiments of the invention are represented in
the drawings and are explained in more detail in the following
description.
[0014] In this case, in the drawing, schematically in each
case,
[0015] FIG. 1 shows a cross section through a turbomachine
according to the invention in the region of a stator blade,
[0016] FIG. 2 shows a longitudinal section through the turbomachine
in the region of a stator blade,
[0017] FIG. 3 shows a plan view of a stator blade in the radial
direction,
[0018] FIG. 4 shows a longitudinal section through the turbomachine
in the region of a hub-side step,
[0019] FIG. 5 shows a much schematized view for illustrating a
pitch ratio,
[0020] FIG. 6 shows a view as in FIG. 5, but for illustrating a
wedge angle.
DETAILED DESCRIPTION OF THE DRAWINGS
[0021] According to FIG. 1, a sectioned stator blade 4 is
exemplarily shown in a flow space 1 which is arranged between a
rotor hub 2 and a radial outer wall 3, that is to say the casing.
The statement that in this case it concerns a stator blade 4 is not
to be interpreted with limitation so that other blades, such as
rotor blades, which are arranged in turbomachines, are also to be
covered by the invention.
[0022] As shown in FIG. 1, the stator blade 4 has a so-called lean
curvature which is directed in the circumferential direction, and
wherein a curvature angle .gamma. varies along the radial blade
length, that is to say from the hub 2 towards the radial outer wall
3. In the case of the embodiment which is shown in FIG. 1, the lean
curvature of the stator blade 4 decreases along the radial blade
length from the blade root, that is to say from the hub 2, towards
the blade tip, that is to say towards the outer wall 3. In the case
of the lean curvature of the stator blade 4 it is a positive lean
curvature, i.e. the curvature extends in the direction of rotation
5 of the stator blade 4. The shape of the curved stator blade 4 in
this case preferably represents a generally continuous arc which
forms an acute angle .gamma. with the hub 2 or with the outer wall
3. The curvature angle .gamma. lies between a tangent 7 which lies
against a blade surface 6 at a trailing edge 12 or at a leading
edge 16 of the stator blade 4, and a radial line 9 which extends
orthogonally to the rotational axis 8 of the turbomachine and lies
preferably within a range of
0.degree..ltoreq..gamma..ltoreq.15.degree..
[0023] In FIG. 2, a so-called sweep curvature of the stator blades
4 is shown, by which is understood a curvature in the axial
direction, i.e. parallel to the chord 10 of the stator blades 4.
The sweep curvature in this case is described by a curvature angle
.delta. which varies along the radial blade length and has a
positive value at the hub 2 and a negative value in the region of
the casing 3. A positive value in this case is defined according to
FIG. 2 by the chord 10 extending above a point of intersection 11
with the radial line 9 which extends orthogonally to the rotational
axis 8 of the turbomachine, to the right of the radial line 9,
while in the case of a negative curvature angle .delta. the chord
extends above the point of intersection 11 to the left of the
radial line 9. The curvature angle .delta. therefore lies between a
meridional tangent 7 which lies against the blade surface 6 on a
leading edge 16 or on a trailing edge 12, and the radial line 9
which extends orthogonally to the rotational axis 8 of the
turbomachine, and customarily has a value of
15.degree..ltoreq..delta..ltoreq.-20.degree..
[0024] According to the invention, the stator blade 4 also has a
twist in the radial direction of the respective blade 4, which is
shown in FIG. 3. The twist, or the twisting, in this case is
defined by a metal angle .alpha..sub.2 which on the one hand is
arranged between a circumferential line 21, which in the
circumferential direction of the turbomachine connects the
respective trailing edges 12 of the respective stator blades 4, and
on the other hand the tangent to the curvature center line 13 at
the leading edge 16 or at the trailing edge 12 respectively.
Similarly to the sweep curvature or to the lean curvature, the
metal angle .alpha..sub.2 also varies along the radial blade
length, wherein in the region of the hub 2 the angle is larger than
in the region of the casing 3. A range of the metal angle
.alpha..sub.2 which is favorable for the aerodynamic conditions of
the turbomachine in this case is customarily
25.degree..ltoreq..alpha..sub.2.ltoreq.10.degree..
[0025] In FIG. 4, a longitudinal section in the region of the
stator blade 4 through the turbomachine is shown, wherein a
hub-side circumferential step 14 is to be seen, which in the
direction of flow 15 falls away inwards and radially to the
rotational axis 8 of the turbomachine. The circumferential step 14,
according to the view in FIG. 4, has an S-shaped profile between
the leading edge 16 and the trailing edge 12. This profile,
however, is not compulsory, it can alternatively also have a linear
progression between the leading edge 16 and trailing edge 12. As a
result of the circumferential step 14, a hub diameter at the
leading edge 16 is larger than at the trailing edge 12, as a result
of which the aerodynamic properties are also positively influenced.
A height of the circumferential step 14 in this case is determined
by the angles .beta..sub.1 and .beta..sub.2 which are determined in
each case between a tangent 7 to the circumferential step 14 on the
one hand, and the rotational axis 8 of the turbomachine or a line
parallel to it on the other hand, and customarily lies within a
range of -20.degree..ltoreq..beta..sub.1,2.ltoreq.20.degree.. In
this case, the tangent 7 to the circumferential step 14 has its
greatest gradient at a point of intersection 17 at which the said
tangent 7, a center of gravity line 18 and the circumferential step
intersect. In the case of an S-shaped cross-sectional form of the
circumferential step 14, the point of inflection of the
circumferential step customarily also lies at the said point of
intersection 17.
[0026] In FIG. 5, a pitch ratio t/s is shown, i.e. the quotient of
blade spacing t in the circumferential direction between two
adjacent stator blades 4 and the chord length s over the radial
extent of the stator blade 4. Both the chord length s and the blade
spacing t in this case are recorded as linear values and can vary
over the radial extent of the stator blade 4, wherein the pitch
ratio t/s is customarily smaller at the blade root 2 than at the
blade tip 3. A range within which the pitch ratio t/s customarily
lies in this case is defined between
0.45.ltoreq.t/s.ltoreq.0.75.
[0027] In the view in FIG. 6, two further special features of the
stator blades 4 according to the invention are shown, specifically
an incidence angle .alpha..sub.1 which varies over the radial blade
length of the stator blade 4 on the one hand, and also a wedge
angle WE which varies over the radial blade length between a
surface tangent 7a to a pressure side 19 and a surface tangent 7b
to a suction side 20 at the trailing edge 12 of the stator blade 4.
In this case, the inflow-side incidence angle .alpha..sub.1 of the
curvature center line 13 at the blade root 2 is smaller than at the
blade tip 3 and for example lies within a range of
55.degree..ltoreq..alpha..sub.1.ltoreq.110.degree.. The incidence
angle .alpha..sub.1 therefore increases from the blade root 2
towards the blade tip 3. In contrast, the wedge angle WE at the
blade root 2 is larger than at the blade tip 3 and decreases
preferably continuously from the blade root 2 in the direction of
the blade tip 3. The wedge angle WE customarily lies within a range
of 15.degree..ltoreq.WE.ltoreq.0.degree..
[0028] It is worthy of note in this case that the stator blades 4
are formed in such a way that at least the curvature angle .gamma.
of the lean curvature and/or the curvature angle .delta. of the
sweep curvature do not change along the radial blade length
provided that the angles are measured with regard to the curvature
center line 13 or with regard to the leading edge 16.
[0029] According to FIG. 6, a narrowest flow cross section q
between two adjacent stator blades 4 is defined, which shifts
between hub 2 and casing 3 against the direction of flow 15. In
other words, this means that the flow bottleneck q at the hub 2 of
two adjacent stator blades lies in the region of a trailing edge
12, while in the region of the casing 3 of two adjacent stator
blades 4 the flow bottleneck lies more in the region of the leading
edges 16.
[0030] An angle .DELTA..alpha. is defined according to FIG. 6, by
the tangent 7' on the one hand and by the tangent 7'' on the other
hand. The tangent 7' lies against the suction side 20 of the
trailing edge 12, while the tangent 7'' lies against the suction
side 20 of the stator blade 4 and at the same time is oriented
orthogonally to the flow bottleneck q. The angle .DELTA..alpha. in
this case decreases according to the invention from the hub 2
towards the casing 3 and is variable along the radial blade length.
A typical range for the angle .DELTA..alpha. in this case lies
between -5.degree..ltoreq..DELTA..alpha..ltoreq.15.degree..
LIST OF DESIGNATIONS
[0031] 1 Flow space [0032] 2 Hub of the turbomachine [0033] 3
Radial outer wall/casing [0034] 4 Stator blade [0035] 6 Blade
surface [0036] 7 Tangent [0037] 8 Rotational axis of the
turbomachine [0038] 9 Radial line [0039] 10 Blade chord [0040] 11
Point of intersection [0041] 12 Trailing edge [0042] 13 Curvature
center line [0043] 14 Hub contour [0044] 15 Direction of flow
[0045] 16 Leading edge [0046] 17 Point of intersection [0047] 18
Center of gravity line [0048] 19 Pressure side of the stator blade
4 [0049] 20 Suction side of the stator blade 4 [0050] 21
Circumferential line [0051] .alpha..sub.1 Metal angle at the blade
leading edge [0052] .alpha..sub.2 Metal angle at the blade trailing
edge [0053] .beta. Angle to the hub contour 14 [0054] .gamma. Lean
curvature angle [0055] .delta. Sweep curvature angle [0056] s Chord
length [0057] t Blade spacing [0058] q Narrowest flow cross section
[0059] WE Wedge angle
* * * * *