U.S. patent application number 11/330332 was filed with the patent office on 2006-11-02 for turbine blade.
Invention is credited to Eiji Saitou, Kiyoshi Segawa, Shigeki Senoo, Sou Shioshita, Yoshio Sikano.
Application Number | 20060245918 11/330332 |
Document ID | / |
Family ID | 11737820 |
Filed Date | 2006-11-02 |
United States Patent
Application |
20060245918 |
Kind Code |
A1 |
Senoo; Shigeki ; et
al. |
November 2, 2006 |
Turbine blade
Abstract
The invention is intended to reduce the profile loss. For that
purpose, according to the invention, a plurality of turbine blades
are arranged in the circumferential direction of a turbine driven
by a working fluid. Each of the turbine blade is formed such that
the curvature of a blade suction surface, which is defined by the
reciprocal of the radius of curvature of a blade surface on the
blade suction surface side, is decreased monotonously from a blade
leading edge defined as the upstream-most point of the blade in the
axial direction toward a blade trailing edge defined as the
downstream-most point of the blade in the axial direction.
Inventors: |
Senoo; Shigeki; (Hitachi,
JP) ; Sikano; Yoshio; (Hitachinaka, JP) ;
Saitou; Eiji; (Hitachi, JP) ; Segawa; Kiyoshi;
(Hitachi, JP) ; Shioshita; Sou; (Hitachinaka,
JP) |
Correspondence
Address: |
MATTINGLY, STANGER, MALUR & BRUNDIDGE, P.C.
1800 DIAGONAL ROAD
SUITE 370
ALEXANDRIA
VA
22314
US
|
Family ID: |
11737820 |
Appl. No.: |
11/330332 |
Filed: |
January 12, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10492132 |
Apr 7, 2004 |
7018174 |
|
|
PCT/JP01/08885 |
Oct 10, 2001 |
|
|
|
11330332 |
Jan 12, 2006 |
|
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Current U.S.
Class: |
415/191 |
Current CPC
Class: |
F01D 9/041 20130101;
Y10S 416/02 20130101; F01D 5/145 20130101; F01D 5/141 20130101 |
Class at
Publication: |
415/191 |
International
Class: |
F01D 9/00 20060101
F01D009/00 |
Claims
1. A turbine blade which is arranged in plural in the
circumferential direction of a turbine driven by a working fluid,
wherein said turbine blade is formed such that the dimensionless
blade suction surface curvature, which is defined as a value
resulting from multiplying the reciprocal of the radius of
curvature of a blade surface on the blade suction surface side by a
pitch defined by the distance between two adjacent blades in the
circumferential direction, is set to a constant value in a region
from a blade leading edge defined as the upstream-riost point of
the blade in the axial direction toward a point most projecting on
the blade suction surface side and is decreased monotonously from
said point most projecting on the blade suction surface side toward
a point where the distance to a pressure surface of another
adjacent blade is minimized.
2. A turbine blade according to claim 1, wherein, assuming that a
point at which a vertical line drawn from the blade trailing edge
toward a tangential line with respect to the blade suction surface
at the blade trailing edge crosses a blade pressure surface is
defined as a trailing edge of the blade pressure surface, an angle
at which the tangential line with respect to the blade suction
surface at the blade trailing edge and a tangential line with
respect to the blade pressure surface at the blade pressure-surface
trailing edge cross each other is set to be not larger than 6
degrees.
3. A turbine blade according to claim 1, wherein the dimensionless
blade suction surface curvature, which is defined as a value
resulting from multiplying the curvature of the blade suction
surface at the trailing leading edge by a pitch defined by the
distance between two adjacent blades in the circumferential
direction, is set to a certain value between 6 and 9.
4. A turbine blade according to claim 1, wherein the dimensionless
blade suction surface curvature, which is defined as a value
resulting from multiplying the curvature of the blade suction
surface at a throat position, defined as a position where an
inter-blade flow passage is narrowest, by a pitch, is set to a
value between 0.5 and 1.5.
5. A turbine comprising a plurality of stator blades and moving
blades arranged in the circumferential direction of a rotor, a row
of said stator blades and a row of said moving blades constituting
a turbine stage, wherein said stator blades are each formed such
that the dimensionless blade suction surface curvature, which is
defined as a value resulting from multiplying the reciprocal of the
radius of curvature of a blade surface on the blade suction surface
side by a pitch defined by the distance between two adjacent blades
in the circumferential direction is set to a constant value from a
blade leading edge defined as the upstream-most point of the blade
in the axial direction toward a point most projecting on the blade
in the axial direction toward a point most projection on the blade
suction surface side, and is decreased monotonously from said point
most projecting on the blade suction surface side toward a point
where the distance to a pressure surface of another adjacent blade
is minimized.
Description
[0001] This application is a continuation of U.S. application Ser.
No. 10/492,132, filed Apr. 7, 2004 and allowed Oct. 31, 2005, the
entirety of which is incorporated herein by reference.
TECHNICAL FIELD
[0002] The present invention relates to a turbine blade for use in
turbo machines, such as a steam turbine and a gas turbine, which
are driven by a working fluid.
BACKGROUND ART
[0003] As disclosed in U.S. Pat. No. 5,445,498, for example, there
is known a multi-arc blade in which a plurality of arcs and
straight lines are connected to each other such that only a
gradient is continuous at respective junctions between adjacent two
of those arcs and straight lines. As represented by such a
multi-arc blade, the profile of a known turbine blade has not been
designed so as to keep continuity in the curvature of a blade
surface from a leading edge to a trailing edge thereof. The
multi-arc blade is relatively easy to design and manufacture, but
it is disadvantageous in that a pressure distribution along the
blade surface is distorted at points where the curvature is
discontinuous and a surface boundary layer is thickened with the
distortion, thus resulting in a larger profile loss.
[0004] Regarding other known turbine blade than the multi-arc
blade, JP A 6-1014106, for example, discloses a design method
comprising the steps of arranging arcs along a camber line of a
blade and forming a profile of the blade as a circumscribed curve
with respect to a group of those arcs. According to that design
method, a leading edge and a trailing edge are each formed in an
arc shape, but the curvature is discontinuous at junctions between
those arc-shaped portions and other adjacent portions forming the
blade profile. Hence, the curvature of the blade leading edge is
extremely large, while the curvature of the blade surface is
reduced in a portion just downstream of the blade leading edge. For
that reason, if an inflow angle differs from the design setting
point of the blade, a boundary layer is thickened or peeled off at
the point where the curvature is discontinuous, thus causing a
profile loss.
[0005] Further, in an area where a curvature distribution along the
blade surface increases or decreases from the upstream toward
downstream side, the blade surface pressure is reduced at a maximum
point of the curvature, and an inverse pressure gradient occurs
downstream of that point. Therefore, a boundary layer is thickened
or peeled off, thus resulting in a larger profile loss.
[0006] Moreover, U.S. Pat. No. 4,211,516, for example, discloses a
blade profile in which a trailing-edge wedge angle formed by a
suction surface near a blade trailing edge and a tangential line
with respect to a pressure surface is as large as about 10 degrees.
In such a blade profile, a fluid flowing along the blade suction
surface and a fluid flowing along the blade pressure surface
collide against each other at the trailing edge, thus resulting in
a larger profile loss.
[0007] An object of the present invention is to provide a turbine
blade capable of reducing the profile loss.
DISCLOSURE OF THE INVENTION
[0008] To achieve the above object, the present invention provides
a turbine blade which is arranged in plural in the circumferential
direction of a turbine driven by a working fluid, wherein the
turbine blade is formed such that the curvature of a blade suction
surface, which is defined by the reciprocal of the radius of
curvature of a blade surface on the blade suction surface side, is
decreased monotonously from a blade leading edge defined as the
upstream-most point of the blade in the axial direction toward a
blade trailing edge defined as the downstream-most point of the
blade in the axial direction.
BRIEF DESCRIPTION OF DRAWINGS
[0009] FIG. 1 plots a distribution of the dimensionless suction
surface curvature of a blade according to one embodiment of the
present invention.
[0010] FIG. 2 is a sectional view of a turbine stage taken along a
meridional plane.
[0011] FIG. 3 shows a construction of a blade row according to the
embodiment.
[0012] FIG. 4 plots a distribution of the blade surface pressure in
a known blade.
[0013] FIG. 5 plots an ideal distribution of the blade surface
pressure.
[0014] FIG. 6 plots a distribution of the blade surface pressure in
the embodiment.
[0015] FIG. 7 shows a wedge angle at a blade trailing edge.
[0016] FIG. 8 illustrates a loss generating mechanism in an area
near the blade trailing edge.
BEST MODE FOR CARRYING OUT THE INVENTION
[0017] A turbine blade of the present invention is arranged in
plural in the circumferential direction of a turbine, such as a
steam turbine and a gas turbine, with the intention of taking out,
as rotating forces, power by using gas (e.g., combustion gas, steam
or air) or a liquid as a working fluid. One embodiment of the
present invention will be described below with reference to the
drawings.
[0018] FIG. 2 shows a turbine stage, comprising a stator blade and
a moving blade, of a turbo machine with the intention of taking
out, as rotating forces, power by utilizing a working fluid. A
stator blade 1 is fixed at its inner peripheral side to a diaphragm
3 and at its outer peripheral side to a diaphragm 4. The diaphragm
4 is fixed at its outer peripheral side to a casing 5. A moving
blade 2 is fixed at its inner peripheral side to a rotor 6 serving
as a rotating part, and its outer peripheral side is positioned to
face the diaphragm 4 with a gap left between them. A working fluid
7 flows in a direction toward the moving blade side from the stator
blade 1 side of the turbine stage. The direction from which the
working fluid 7 flows in is defined as the upstream side in the
axial direction, and the direction in which the working fluid 7
flows out is defined as the downstream side in the axial
direction.
[0019] FIG. 3 shows a construction of row of turbine blades (stator
blades) according to this embodiment. A static pressure P2
downstream of the blade is smaller than a total pressure PO
upstream of the blade. Therefore, a flow of the working fluid comes
into the turbine in the axial direction and is bent in the
circumferential direction along an inter-blade flow passage formed
between two blades, whereby the flow is accelerated. Thus, the
blade serves to convert a high-pressure, low-speed fluid at a blade
inlet into a low-pressure, high-speed fluid. In other words, the
blade serves to convert thermal energy of a high-pressure fluid
into kinetic energy. In practice, however, the efficiency of such
energy conversion is not 100%, and a part of the thermal energy is
dissipated as a loss not available as work. To compensate for the
loss, the high-pressure fluid must be introduced to flow into the
turbine at a larger flow rate. Extra energy to be added
correspondingly is increased as the loss increases. Stated another
way, energy required for taking out the same amount of power is
decreased as the loss decreases.
[0020] Regarding a blade operating in a subsonic region, losses
attributable to a profile of the blade are mainly divided into a
frictional loss due to friction that is generated between the fluid
and a blade surface, and a trailing edge loss caused at a blade
trailing edge having a finite thickness. The frictional loss is
determined depending on a blade surface area and a pressure
distribution along the blade surface. Namely, the frictional loss
is increased as the blade surface area increases, and it is also
increased as an inverse pressure gradient along the blade surface
increases. Also, the trailing edge loss is substantially determined
depending on a trailing edge thickness and a trailing-edge wedge
angle of the blade. Because the trailing edge thickness and the
trailing-edge wedge angle are each set to a minimum value allowable
from the viewpoint of blade strength, the frictional loss is
decreased as the number of blades decreases. Further, because
energy that must be converted by an overall blade periphery, i.e.,
a blade load, is determined in the stage of design, a reduction in
the number of blades corresponds to an increase in the blade load
per blade. Even in the case of increasing the blade load per blade,
if the size of one blade is increased, the surface area of the
blade is also increased. Thus, an increase in the blade load per
unit area of the blade results in a loss reduction. From the above
description, it is understood that the energy conversion efficiency
of the blade can be effectively increased by (1) increasing the
blade load per unit area of the blade, and (2) reducing the inverse
pressure gradient along the blade surface.
[0021] FIG. 4 plots one example of a distribution of the blade
surface pressure in a prior-art blade. P0 indicates a total
pressure at an inlet, p2 indicates a static pressure at an outlet
of the blade row, and pmin indicates a minimum pressure value along
the blade surface. A curve representing a higher pressure denoted
by PS is called a pressure surface, and a blade surface providing a
lower pressure denoted by SS is called a suction surface. LE
indicates a blade leading edge, and TE indicates a blade trailing
edge. The blade load is equal to an area surrounded by PS and SS
between LE and TE. Further, an amount indicated by dp represents a
pressure difference between p2 and pmin. With an increase of dp,
there occurs a pressure rise from pmin to p2 along the blade
surface, i.e., an inverse pressure gradient. The inverse pressure
gradient increases the thickness of a boundary layer or induces
peeling-off of the boundary layer, thus resulting in a larger loss.
If the number of conventional blades is decreased to reduce both
the frictional losses and the trailing edge losses of the blades,
an increase in the blade load per blade is concentrated in the
downstream side of the blade and the inverse pressure gradient is
increased. Hence, a larger loss is resulted contrary to the
intention. For those reasons, dp must be kept small.
[0022] As is apparent from the above description, in order to
increase the blade load per unit area of the blade in the blade
having the blade load distribution shown in FIG. 4, it is effective
to increase the blade load in the upstream side of the blade where
the blade load is small in the prior art.
[0023] FIG. 5 plots a pressure distribution of an ideal blade, in
which dp is made 0 and the blade load is increased. The blade
surface pressure is equal to the total pressure at the inlet over
the entire pressure surface and is equal to the static pressure at
the outlet over the entire suction surface. This is an ideal
distribution of the blade surface pressure. However, such an ideal
distribution cannot be realized in practice because there occurs a
discontinuity in pressure at the leading edge and the trailing
edge.
[0024] FIG. 6 plots a distribution of the blade surface pressure in
the blade according to the embodiment shown in FIG. 3. As seen, the
distribution of the blade surface pressure in the embodiment shown
in FIG. 3 is closer to the ideal pressure distribution shown in
FIG. 5. Comparing with the pressure distribution in the prior art
shown in FIG. 4, it is understood that, in this embodiment, since
the pressure on the suction surface (SS) side is reduced in the
upstream side of the blade to increase the blade load, the blade
load distribution per unit area can be increased without increasing
the pressure difference dp between the static pressure P2 at the
outlet of the blade row and the minimum pressure value pmin along
the blade surface. The distribution of the blade surface pressure
can be controlled depending on the curvature of the blade
surface.
[0025] This is because, assuming the curvature of the wall surface
to be defined by the reciprocal 1/r of the radius r of the
curvature, the relationship between the curvature 1/r of the wall
surface and a local pressure gradient can be expressed as given
below using a density .rho. and a speed V:
.rho.V.sup.2/r=.delta.p/.delta.r More specifically, the pressure at
the wall surface is proportional to the product of the square of
the speed near the wall surface and the curvature 1/r. The
inter-blade flow in the turbine is an accelerated flow having a low
flow speed at the inlet and a high flow speed at the outlet.
Therefore, it is required to increase the curvature in order to
lower the pressure at the inlet where the flow speed is low, and to
decrease the curvature in order to make constant the pressure at
the outlet where the flow speed is high. Thus, the pressure
distribution along the blade suction surface, shown in FIG. 6, can
be realized by monotonously decreasing the curvature of the blade
suction surface in match with a monotonous increase of the flow
speed.
[0026] FIG. 1 plots a distribution of the suction surface curvature
of the turbine blade according to this embodiment. The horizontal
axis represents the direction of a rotation axis, and the vertical
axis represents the dimensionless suction surface curvature
resulting from multiplying the curvature of the blade surface by a
pitch t, i.e., the distance between two blades. As shown in FIG. 1,
in the turbine blade according to this embodiment, the curvature of
the blade surface decreases monotonously and continuously from the
leading edge toward the trailing edge of the blade. Stated another
way, according to this embodiment, in each of a plurality of blades
arranged in the circumferential direction of a turbine driven for
taking out power, as rotating forces, by utilizing a working fluid,
the turbine blade is formed such that the curvature of a blade
suction surface, which is defined by the reciprocal of the radius
of curvature of a blade surface on the blade suction surface side,
is decreased continuously and monotonously from a blade leading
edge defined as the upstream-most point of the blade in the axial
direction toward a blade trailing edge defined as the
downstream-most point of the blade in the axial direction.
Incidentally, when a portion of the blade near the blade trailing
edge is in the form of a single arc, the blade trailing edge is
defined as the downstream-most point of the blade except for that
arc-shaped portion.
[0027] Thus, according to this embodiment, geometrical conditions
of the blade profile for realizing an improvement of the efficiency
is derived on the basis of fluid physics. As a result, the turbine
blade of this embodiment is able to improve the efficiency of
conversion from thermal energy of the fluid into kinetic energy or
the efficiency of conversion from the kinetic energy into rotation
energy of the rotor.
[0028] As seen from FIG. 6 plotting a distribution of the blade
surface pressure resulting when the blade suction surface is formed
so as to have the curvature distribution shown in FIG. 1, this
embodiment can provide not only a relatively small inverse pressure
gradient, but also the pressure distribution closer to the ideal
pressure distribution shown in FIG. 5. Further, as a result of
actually conducting a wind-tunnel test on the blade row, a
reduction of loss was confirmed in comparison with the blade having
the distribution of the blade surface pressure shown in FIG. 4.
[0029] The distribution of the blade suction surface curvature,
plotted in FIG. 1, for realizing the pressure distribution plotted
in FIG. 6, will be described in more detail below with reference to
the blade profile shown in FIG. 3 for comparison.
[0030] First, in a region from a blade leading edge position A
shown in FIG. 3 to a point B most projecting to the blade suction
surface side, the dimensionless blade suction surface curvature,
which is defined as a value resulting from multiplying the
curvature of the blade surface by the pitch, i.e., the distance
between two adjacent blades in the circumferential direction, is
set to a certain value between 6 and 9 so that the pressure
decreases in an area where the flow speed is low, taking into
account the fact that the profile loss is not increased with
thickening or peeling-off of the boundary layer along the blade
surface even when the inflow angle with respect to the blade
greatly differs from the design inflow angle of 90 degrees. In the
embodiment shown in FIG. 1, the dimensionless blade suction surface
curvature in the region from A to B is set to about 7.
[0031] If the dimensionless blade suction surface curvature in the
region from A to B is smaller than 6, the effect obtainable with
the present invention is reduced because the blade surface pressure
near the blade leading edge is not decreased and the blade load per
unit area cannot be increased. Also, a small value of the
dimensionless blade suction surface curvature at the leading edge
means that the radius of the blade leading edge is large and hence
the size of the blade itself is increased, thus resulting in a
larger blade surface area. On the other hand, if the dimensionless
blade suction surface curvature is larger than 9, the blade surface
pressure near the blade leading edge partly becomes lower than the
pressure P2 at the outlet of the blade row. Consequently, there
occurs an inverse pressure gradient in some area and the effect
obtainable with the present invention is reduced.
[0032] Then, at a throat C defined as the point where the distance
to the pressure surface of another adjacent blade is minimized, the
dimensionless blade suction surface curvature is set to a value
between 0.5 and 1.5. In the embodiment shown in FIG. 1, the
dimensionless blade suction surface curvature at the throat C is
set to about 0.8. If the dimensionless blade suction surface
curvature is set larger than 1.5, the blade surface pressure is
decreased because the flow speed is high at the throat C.
Consequently, the inverse pressure gradient dp is increased in an
area from the throat toward the trailing edge and the effect
obtainable with the present invention is reduced. Also, the
curvature of the blade suction surface at the throat is related to
a throttle rate of the inter-blade flow passage at the throat. If
the dimensionless blade suction surface curvature at the throat is
smaller than 0.5, the throttle rate of the inter-blade flow passage
at the throat is reduced, whereby the flow speed upstream of the
throat is increased and hence the position at which the blade
surface pressure is minimized along the blade suction surface is
located upstream of the throat. Consequently, the iriverse pressure
gradient occurs in a longer range from the throat toward the
trailing edge and the effect obtainable with the present invention
is reduced.
[0033] Further, in a region from the point B most projecting to the
blade suction surface side to the throat C, the dimensionless blade
suction surface curvature requires to be set so as to decrease
monotonously and continuously. In this region, if the dimensionless
blade suction surface curvature has an inflection point, undulation
generates in the distribution of the blade surface pressure and the
boundary layer along the blade surface is thickened in some cases.
For this reason, the dimensionless blade suction surface curvature
in the region from the point B most projecting to the blade suction
surface side to the throat C is preferably provided as a straight
line or a curve expressed by a function of the second degree, which
has no inflection point, or a curve expressed by a function of the
third degree, which has only one inflection point. In addition,
because the boundary layer along the blade suction surface
downstream of the throat is thickened in an increasing amount and
tends to more easily peel off toward the trailing edge, the
dimensionless blade suction surface curvature downstream of the
throat is more preferably decreased monotonously such that a
reduction rate of the curvature decreases toward the trailing
edge.
[0034] The wedge angle at the trailing edge of the turbine blade
according to this embodiment will be described below with reference
to FIG. 7. On an assumption that a point TEp at which a vertical
line lsp drawn from a blade trailing edge TE toward a tangential
line Is with respect to a blade suction surface SS at the blade
trailing edge TE crosses a blade pressure surface PS is defined as
a trailing edge of the blade pressure surface, a trailing-edge
wedge angle WE is defined as an angle at which the tangential line
Is with respect to the blade suction surface at the blade trailing
edge TE and a tangential line lp with respect to the blade pressure
surface at the blade pressure-surface trailing edge cross each
other.
[0035] FIG. 8 schematically illustrates a loss generating mechanism
in an area near the blade trailing edge. When a flow fs along the
blade suction surface and a flow fp along the blade pressure
surface collide against each other in an area downstream of the
blade trailing edge, kinetic energy of the fluid dissipates as
thermal energy, thus causing a profile loss. The kinetic energy
lost upon the collision of those two flows is greatly affected by
the magnitudes of speed components opposed to each other, and these
speed components are in proportion to the trailing-edge wedge
angle. From the viewpoint of reducing the profile loss, therefore,
the trailing-edge wedge angle is preferably as small as possible.
Thus, the trailing-edge wedge angle is required to be not larger
than 6 degrees for realizing the pressure distribution according to
this embodiment, plotted in FIG. 6, and suppressing the generation
of loss at the trailing edge.
[0036] With the turbine blade of this embodiment, as described
above, since the curvature of the blade suction surface is
decreased monotonously from the leading edge to the blade trailing
edge, the pressure along the blade suction surface can be reduced
near the leading edge and can be made constant near the throat at a
value substantially equal to the outlet static pressure. Therefore,
the inverse pressure gradient can be suppressed small and the blade
load per blade can be increased. It is hence possible to reduce the
number of blades and to minimize both the blade surface area
related to the frictional loss and the area of the blade trailing
edge related to the trailing edge loss. As a result, the profile
loss given as the sum of the frictional loss and the trailing edge
loss can be reduced, and the turbine efficiency can be
improved.
[0037] While the turbine blade of the present invention is suitably
applied to a stator blade of a steam turbine, the present invention
is not limited to such an application.
INDUSTRIAL APPLICABILTY
[0038] The turbine blade of the present invention is employed in
the power generation field for production of electric power.
* * * * *