U.S. patent application number 15/503806 was filed with the patent office on 2017-09-14 for centrifugal impeller and centrifugal compressor.
This patent application is currently assigned to MITSUBISHI HEAVY INDUSTRIES, LTD.. The applicant listed for this patent is MITSUBISHI HEAVY INDUSTRIES COMPRESSOR CORPORATION, MITSUBISHI HEAVY INDUSTRIES, LTD.. Invention is credited to Daisuke HIRATA, Jo MASUTANI.
Application Number | 20170260998 15/503806 |
Document ID | / |
Family ID | 55532866 |
Filed Date | 2017-09-14 |
United States Patent
Application |
20170260998 |
Kind Code |
A1 |
MASUTANI; Jo ; et
al. |
September 14, 2017 |
CENTRIFUGAL IMPELLER AND CENTRIFUGAL COMPRESSOR
Abstract
The impeller provides that when an angle made by a projection
line 33 that is obtained by projecting a camber line 32 of the
blade 22 onto a predetermined meridional cross section and the
camber line 32 is defined as an inclination angle .gamma..theta.
and an inclination in a direction opposite to a rotating direction
of the rotary shaft is defined to be positive, the blade 22 is
formed in such a manner that the inclination angle .gamma..theta.
of a leading edge 22A is zero or positive on the hub 20 side and
gradually increasing toward the shroud 21 and the inclination angle
is gradually decreasing from the leading edge toward a trailing
edge in a flow direction of the fluid.
Inventors: |
MASUTANI; Jo; (Tokyo,
JP) ; HIRATA; Daisuke; (Hiroshima-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MITSUBISHI HEAVY INDUSTRIES, LTD.
MITSUBISHI HEAVY INDUSTRIES COMPRESSOR CORPORATION |
Tokyo
Tokyo |
|
JP
JP |
|
|
Assignee: |
MITSUBISHI HEAVY INDUSTRIES,
LTD.
Tokyo
JP
MITSUBISHI HEAVY INDUSTRIES COMPRESSOR CORPORATION
Tokyo
JP
|
Family ID: |
55532866 |
Appl. No.: |
15/503806 |
Filed: |
March 26, 2015 |
PCT Filed: |
March 26, 2015 |
PCT NO: |
PCT/JP2015/059344 |
371 Date: |
February 14, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F04D 29/30 20130101;
F04D 29/4206 20130101; F04D 29/284 20130101; F05D 2240/303
20130101; F04D 29/681 20130101; F05D 2250/70 20130101; F05D
2240/304 20130101 |
International
Class: |
F04D 29/30 20060101
F04D029/30; F04D 29/42 20060101 F04D029/42; F04D 29/28 20060101
F04D029/28 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 18, 2014 |
JP |
2014-190468 |
Claims
1. A centrifugal impeller comprising: a hub; a shroud; and a
plurality of blades disposed between the hub and the shroud, the
centrifugal impeller blowing out fluid in a radial direction by
rotation of a rotary shaft fixed to the hub, wherein when an angle
made by a projection line that is obtained by projecting a camber
line of the blade onto a predetermined meridional cross section and
the camber line is defined as an inclination angle and an
inclination in a direction opposite to a rotating direction of the
rotary shaft is defined to be positive, the blade is formed in such
a manner that the inclination angle of a leading edge is zero or
positive on a hub side and gradually increasing toward the shroud
and the inclination angle is gradually decreasing from the leading
edge toward a trailing edge in a flow direction, and the
inclination angle of the trailing edge in the blade is zero or
positive on the hub side and gradually increasing toward the
shroud.
2. (canceled)
3. The centrifugal impeller according to claim 1, wherein the
inclination angle of the trailing edge in the blade is zero or
positive over a region from the hub side to the shroud side.
4. The centrifugal impeller according to claim 1, wherein the
leading edge of the blade, when projected onto the meridional cross
section, has a linear shape from the hub side to the shroud side or
a shape protruded toward an upstream side of the flow direction
between the hub side and the shroud side.
5. A centrifugal compressor comprising the centrifugal impeller
according to claim 1.
6. The centrifugal impeller according to claim 3, wherein the
leading edge of the blade, when projected onto the meridional cross
section, has a linear shape from the hub side to the shroud side or
a shape protruded toward an upstream side of the flow direction
between the hub side and the shroud side.
7. A centrifugal compressor comprising the centrifugal impeller
according to claim 3.
8. A centrifugal compressor comprising the centrifugal impeller
according to claim 4.
Description
FIELD
[0001] The present invention relates to a centrifugal impeller and
a centrifugal compressor including the centrifugal impeller.
BACKGROUND
[0002] Centrifugal compressors for industrial use are generally
used in petrochemical plants or natural gas plants, for example. A
centrifugal compressor of this type employs a centrifugal impeller
for blowing out fluid in a radial direction by the rotation of a
rotary shaft, including a hub fixed to the rotary shaft and a
plurality of blades disposed in the hub (see Patent Literature 1,
for example).
CITATION LIST
Patent Literature
[0003] Patent Literature 1: Japanese Patent Application Laid-Open
No. 2004-044473
SUMMARY
Technical Problem
[0004] According to a conventional configuration, when a blade 100
of a centrifugal impeller is viewed from an intake port 101 side,
the blade 100 is formed in such a manner that an angle made by a
camber line 103 of a leading edge 102 and a straight line 104
extending in a radial direction from the center of rotation is
approximately 0.degree. over a region from a wall surface 105 on a
hub side to a wall surface 106 on a shroud side as shown in FIG.
11. When the blade 100 is viewed from a blowoff port 107 side, the
blade latter half of the blade 100 including a trailing edge 108
inclines obliquely in such a manner that a suction surface S of the
blade 100 faces the wall surface 106 on the shroud side as shown in
FIG. 12.
[0005] By the way, in the centrifugal impeller of this type, a
boundary layer 109 is generated on the wall surface 106 on the
shroud side, which constitutes a passage for fluid. The boundary
layer 109 develops in a deceleration zone of the wall surface 106
on the shroud side in the first half of the blade. Also on a
surface of the blade 100, a boundary layer develops, starting from
the leading edge 102, on the suction surface S having larger
deceleration than a pressure surface P to which a positive pressure
is applied by the rotation. This boundary layer is attracted to a
radially upper part by centrifugal force, thereby flowing into and
merging with the boundary layer 109 generated on the wall surface
106 on the shroud side. Thus, the boundary layer 109 on the wall
surface 106 on the shroud side develops further. The thus developed
boundary layer develops further also in the latter half of the
blade, thereby creating a large energy deficit portion on a blade
outlet side. Thus, it is expected to deteriorate the performance of
the centrifugal impeller. The conventional configuration, however,
has made no contraption for suppressing the boundary layer 109
developed on the wall surface 106 on the shroud side in the first
half of the blade, in particular.
[0006] The present invention has been made in view of such
circumstances, and it is an object of the present invention to
provide a centrifugal impeller capable of suppressing the
development of a boundary layer and thus fulfilling its performance
sufficiently, and a centrifugal compressor.
Solution to Problem
[0007] According to an aspect of the present invention, a
centrifugal impeller comprises: a hub; a shroud; and a plurality of
blades disposed between the hub and the shroud, the centrifugal
impeller blowing out fluid in a radial direction by rotation of a
rotary shaft fixed to the hub. When an angle made by a projection
line that is obtained by projecting a camber line of the blade onto
a predetermined meridional cross section and the camber line is
defined as an inclination angle and an inclination in a direction
opposite to a rotating direction of the rotary shaft is defined to
be positive, the blade is formed in such a manner that the
inclination angle of a leading edge is zero or positive on the hub
side and gradually increasing toward the shroud and the inclination
angle is gradually decreasing from the leading edge toward a
trailing edge in a flow direction.
[0008] According to this configuration, the inclination angle of
the leading edge in the blade is zero or positive on the hub side
and gradually increasing toward the shroud. Thus, a pressure
surface of the blade faces the shroud in a portion of the blade
from the leading edge to the first half thereof. Consequently, a
boundary layer is pressed against the shroud by force of the
pressure surface of the blade, thereby suppressing the development
of the boundary layer. On a suction surface of the blade, a
boundary layer is pressed against the suction surface by
centrifugal force, thereby preventing its movement toward the
shroud and thus suppressing the development of the boundary layer.
Furthermore, in the flow direction, the blade is formed in such a
manner that the inclination angle is gradually decreasing from the
leading edge toward the trailing edge. Consequently, the surface
area of the blade in the latter half of the blade is reduced, and
thus the amount of the boundary layer developed over the blade
surface in the latter half of the blade can be reduced. This can
suppress the generation of an energy deficit portion on a blade
outlet side, thereby allowing the performance of the centrifugal
impeller to be fulfilled sufficiently.
[0009] In this configuration, the inclination angle of the trailing
edge in the blade is preferably zero or positive on the hub side
and gradually increasing toward the shroud. According to such a
configuration, the pressure surface of the blade faces the shroud
also in the latter half of the blade. Consequently, the boundary
layer is pressed against the shroud by the force of the pressure
surface of the blade, thereby suppressing the development of the
boundary layer.
[0010] Alternatively, the inclination angle of the trailing edge in
the blade is preferably zero or positive over a region from the hub
side to the shroud side. Moreover, such a positive value is
preferably closer to zero. According to such a configuration, the
length of the trailing edge of the blade can be made the shortest
distance, thereby minimizing an amount of wake flow due to the
thickness of the trailing edge of the blade. Furthermore, the
reduced surface area of the blade in the latter half of the blade
can reduce the amount of the boundary layer developed over the
blade surface in the latter half of the blade as compared to the
conventional technique.
[0011] The leading edge of the blade, when projected onto the
meridional cross section, preferably has a linear shape from the
hub side to the shroud side or a shape protruded toward an upstream
side of the flow direction between the hub side and the shroud
side. According to such a configuration, the area of a portion of
the leading edge of the blade facing the shroud can be increased,
thereby more effectively suppressing the development of the
boundary layer accordingly.
[0012] The provision of the above-described centrifugal impeller in
a centrifugal compressor can suppress the generation of the energy
deficit portion on the blade outlet side, thus improving the
compression efficiency of the centrifugal compressor.
Advantageous Effects of Invention
[0013] According to the centrifugal impeller of the present
invention, the blade is formed in such a manner that the
inclination angle of the leading edge is zero or positive on the
hub side and gradually increasing toward the shroud and the
inclination angle is gradually decreasing from the leading edge
toward the trailing edge in the flow direction. Thus, the pressure
surface of the blade faces the shroud in the portion of the blade
from the leading edge to the first half thereof. This can suppress
the development of the boundary layer and thus suppress the
generation of the energy deficit portion on the blade outlet side,
thereby allowing the performance of the centrifugal impeller to be
fulfilled sufficiently.
BRIEF DESCRIPTION OF DRAWINGS
[0014] FIG. 1 is a longitudinal cross-sectional view of a
centrifugal compressor according to the present embodiment.
[0015] FIG. 2 is a partial enlarged view illustrating an
impeller.
[0016] FIG. 3 is a diagram for explaining an inclination angle of a
blade shown on a meridional cross section.
[0017] FIG. 4 is a diagram illustrating the blade projected on the
meridional cross section.
[0018] FIG. 5 is a diagram illustrating an intake port of the
impeller as seen from an axial direction.
[0019] FIG. 6 is a schematic view illustrating the shape of a
leading edge of the blade of the impeller.
[0020] FIG. 7 is a diagram illustrating a blowoff port of the
impeller as seen from a radial direction.
[0021] FIG. 8 is a diagram illustrating the blowoff port of the
impeller as seen from the axial direction.
[0022] FIG. 9 is a schematic view illustrating the shape of a
trailing edge of the blade of the impeller.
[0023] FIG. 10 is an experimental measurement diagram showing
changes in the development of boundary layers due to the shapes of
blades in a conventional technique and the present embodiment.
[0024] FIG. 11 is a schematic view illustrating the shape of a
leading edge of a blade in a conventional impeller.
[0025] FIG. 12 is a schematic view illustrating the shape of a
trailing edge of the blade in the conventional impeller.
DESCRIPTION OF EMBODIMENTS
[0026] An embodiment of the present invention will be described
below with reference to the drawings. Note that this invention is
not limited by the following embodiment. Note also that elements in
the following embodiment encompass those substitutable by and
obvious to a person skilled in the art, or substantially the same
elements.
[0027] FIG. 1 is a longitudinal cross-sectional view of a
centrifugal compressor according to the present embodiment. A
centrifugal compressor 1 includes: a casing 2 formed by a
combination of a plurality of parts; a rotary shaft 5 supported so
as to be rotatable about an axis line L via bearings (not shown) in
the casing 2; and closed type impellers 6 fixed to the rotary shaft
5 so as to rotate integrally with the rotary shaft 5. In other
words, the centrifugal compressor 1 of the present embodiment is a
two-stage centrifugal compressor.
[0028] In the centrifugal compressor 1, the rotary shaft 5 is
driven by a driving mechanism (not shown) to rotate the impellers
6. Consequently, fluid, such as gas or air, to be compressed is
sucked into the centrifugal compressor 1 via a suction port 10
provided in the casing 2. An intake passage 11 is connected to the
suction port 10 via a suction space 10A formed in the casing 2. The
intake passage 11 bends along the direction of the axis line L of
the rotary shaft 5 (axial direction) and has an opening facing an
intake port 6A of the first-stage impeller 6.
[0029] Centrifugal force is imparted to the fluid sucked from the
suction port 10 by the rotation of the first-stage impeller 6. The
kinetic energy of such fluid is converted to pressure energy by a
first-stage vaneless diffuser 12 provided at a blowoff port 6B of
the impeller 6. This fluid is further guided to an intake port 6A
of the second-stage impeller 6, which is the next compression
stage, via a return bend 14 and a return vane 15.
[0030] Similarly, centrifugal force is imparted to such compressed
fluid by the second-stage impeller 6. The kinetic energy of such
fluid is converted to pressure energy by a second-stage vaneless
diffuser 12 and discharged to a scroll 16 as compressed fluid with
a higher pressure. Thereafter, the fluid is sent out from the
scroll 16 to a discharge pipe (not shown) via a discharge port 17
provided in the casing 2. Note that the reference numeral 18 in
FIG. 1 denotes a balance piston provided for adjusting thrust of
the impeller 6. The impeller 6 will be described next.
[0031] FIG. 2 is a partial enlarged view illustrating the impeller.
As shown in FIG. 2, the impeller 6 includes: a hub 20 fixed to the
rotary shaft 5; a shroud 21 disposed with a space from the hub 20
in a radial direction and the axial direction; and a plurality of
blades 22 disposed between the hub 20 and the shroud 21. The blades
22 are disposed radially with a space around the axis line L,
although their graphic representation is omitted. A leading edge
22A of the blade 22 is positioned on the intake port 6A side of the
impeller 6, and a trailing edge 22B extends to the blowoff port 6B
of the impeller 6.
[0032] By the way, a boundary layer is generated on an inner wall
surface 21A of the shroud 21, which constitutes a fluid passage
together with the hub 20, on the intake port 6A side of the
impeller 6. This boundary layer grows (develops) on the inner wall
surface 21A of the shroud 21 when the fluid flows from the leading
edge 22A of the blade 22 toward the trailing edge 22B.
Consequently, a large energy deficit is generated at the blowoff
port (blade outlet side) 6B. Thus, it is expected to deteriorate
the performance of the impeller. In the present embodiment, the
shape of the blade 22 has the following configuration in order to
suppress the growth of the boundary layer.
[0033] An inclination angle required to define the shape of the
blade 22 of the impeller 6 will be described first. FIG. 3 is a
diagram for explaining the inclination angle of the blade shown on
a meridional cross section. FIG. 4 is a diagram illustrating the
blade projected on the meridional cross section. Since the blade 22
of the impeller 6 has a three-dimensional shape, the inclination
angle is expressed with a cylindrical coordinate system shown in
FIGS. 3 and 4.
[0034] In FIGS. 3 and 4, the Z-axis represents the axis line L of
the rotary shaft 5. An r-Z plane formed by the Z-axis and a
straight line r extending from an origin point O at an angle made
by a predetermined angle .theta. from the X-axis represents a
predetermined meridional cross section 30. When the blade 22 is
projected on the meridional cross section 30, a broken line denoted
by the reference numeral 31 is a line (streamline) dividing a
meridional passage into equal areas in a blade span direction.
[0035] In FIG. 3, the reference numeral 32 denotes a camber line of
the blade (for example, the leading edge) before being projected.
When the camber line 32 is projected on the meridional cross
section 30, a projection line (projection line of the camber line
of the blade parallel to the meridional cross section 30) 33 is
formed. An angle made by the projection line 33 and the camber line
32 is defined as the inclination angle of the blade 22 (inclination
angle in a circumferential direction of the blade) .gamma..theta.
in the present embodiment. Note that the positive or negative sign
of the inclination angle .gamma..theta. is defined in accordance
with the rotating direction of the rotary shaft 5. In the present
embodiment, a direction opposite to the rotating direction
(counter-rotating direction) is defined to be positive.
[0036] Note that the reference numeral 34 denotes a projection line
of a camber line of the blade perpendicular to the meridional cross
section 30. An angle .gamma.Z made by the above-described
projection line 33 and the Z-axis (parallel line Z' translated onto
the meridional cross section 30) is defined as an axial tilt angle
of the blade projected onto the meridional cross section 30.
[0037] The shape of the blade 22 will be described next. FIG. 5 is
a diagram illustrating the intake port of the impeller as seen from
the axial direction. FIG. 6 is a schematic view illustrating the
shape of the leading edge of the blade of the impeller. As shown in
FIG. 6, the leading edge 22A is formed in a curved manner so as to
project more on the inner wall surface 21A side of the shroud 21
than on a inner wall surface 20A side of the hub 20. Specifically,
the camber line 32 of the leading edge 22A curves in such a manner
that the inclination angle .gamma..theta. with respect to the
projection line 33 formed on the above-described meridional cross
section 30 (FIG. 3) is approximately zero or positive on the hub 20
side and gradually increasing toward the shroud 21. In such a
configuration, the shroud 21 side of the leading edge 22A of the
blade 22 inclines in the counter-rotating direction. Thus, a
pressure surface P of the blade 22 is disposed so as to face the
inner wall surface 21A of the shroud 21. Furthermore, since the
inclination angle .gamma..theta. gradually increases toward the
shroud 21, the leading edge 22A inclines more on the shroud 21
side, thus facing the inner wall surface 21A of the shroud 21 in a
larger degree. Consequently, gradually toward the shroud 21, force
F generated by the pressure surface P of the blade 22 is headed to
the inner wall surface 21A of the shroud 21. Note that the curve of
the leading edge 22A may be a curve along a single arc or a curve
made by a combination of arcs.
[0038] According to this configuration, the inclination angle
.gamma..theta. of the leading edge 22A in the blade 22 is zero or
positive on the hub 20 side and gradually increasing toward the
shroud 21. Thus, the pressure surface P of the blade 22 faces the
inner wall surface 21A of the shroud 21 in a portion of the blade
22 from the leading edge 22A to the first half thereof in a flow
direction. Consequently, a boundary layer 35 is pressed against the
inner wall surface 21A of the shroud 21 by the force F of the
pressure surface P of the blade 22, thereby suppressing the
development of the boundary layer 35. On a suction surface S side
of the blade 22, a boundary layer 35 generated on the suction
surface S is pressed against the suction surface S by centrifugal
force F1, thereby preventing its movement toward the shroud 21 and
thus suppressing the development of the boundary layer 35.
[0039] The trailing edge 22B side of the blade 22 will be described
next. FIG. 7 is a diagram illustrating the blowoff port of the
impeller as seen from the radial direction. FIG. 8 is a diagram
illustrating the blowoff port as seen from the axial direction.
FIG. 9 is a schematic view illustrating the shape of the trailing
edge of the blade of the impeller. Unlike the leading edge 22A
side, the trailing edge 22B side of the blade 22 is formed in such
a manner that the inclination angle .gamma..theta. of the camber
line 32 with respect to the projection line 33 is approximately
zero or positive. Such a positive value is preferably closer to
zero. A region between the leading edge 22A and the trailing edge
22B in the blade 22 is formed in such a manner that the inclination
angle .gamma..theta. gradually decreases (becomes closer to zero)
along the flow direction of the fluid. In this configuration, the
trailing edge 22B of the blade 22 erects generally perpendicular to
the inner wall surface 20A of the hub 20 and the inner wall surface
21A of the shroud 21, thereby making its height (length) in the
direction of the axis line L the shortest distance. Thus, an amount
of wake flow due to the thickness of the trailing edge 22B of the
blade 22 can be minimized.
[0040] Effects of the present embodiment will be described next.
FIG. 10 is an experimental measurement diagram showing changes in
the development of the boundary layers due to the shapes of the
blades in the conventional technique and the present embodiment. In
FIG. 10, A to C show changes in the boundary layer in the
configuration using the conventional blade 100 (FIGS. 11 and 12). D
to F show changes in the boundary layer in the configuration using
the blade 22 of the present embodiment. Specifically, A and D each
illustrate an amount of the boundary layer at a position before the
outflow port of the impeller. Moreover, B and E each illustrate an
amount of the boundary layer in midstream to the outflow port of
the impeller. Furthermore, C and F each illustrate an amount of the
boundary layer in a middle portion of the length of the blade in
the flow direction.
[0041] In the conventional configuration, an amount of the boundary
layer 109 (a portion with a particularly large pressure loss in an
accumulated development portion of the boundary layer) increases
along the flow direction of the fluid (C.fwdarw.B.fwdarw.A). In the
present embodiment, on the other hand, while an amount of the
boundary layer 35 (a portion with a particularly large pressure
loss in an accumulated development portion of the boundary layer)
slightly increases along the flow direction of the fluid
(F.fwdarw.E.fwdarw.D), the amount of the boundary layer is reduced
significantly as compared to the conventional configuration. Thus,
it can be understood that the growth of the boundary layer (the
portion with a particularly large pressure loss in the accumulated
development portion of the boundary layer) can be suppressed.
[0042] As described above, the impeller 6 according to the present
embodiment is configured to include the hub 20, the shroud 21, and
the plurality of blades 22 disposed between the hub 20 and the
shroud 21 and blow out the fluid in the radial direction by the
rotation of the rotary shaft 5 fixed to the hub 20. When the angle
made by the projection line 33 that is obtained by projecting the
camber line 32 of the blade 22 onto the predetermined meridional
cross section 30 and the camber line 32 is defined as the
inclination angle .gamma..theta. and an inclination in the
direction opposite to the rotating direction of the rotary shaft 5
is defined to be positive, the inclination angle .gamma..theta. of
the leading edge 22A in the blade 22 is zero or positive on the hub
20 side and gradually increasing toward the shroud 21. Thus, the
pressure surface P of the blade 22 faces the inner wall surface 21A
of the shroud 21 in the portion of the blade 22 from the leading
edge 22A to the first half thereof. Consequently, the boundary
layer 35 is pressed against the inner wall surface 21A of the
shroud 21 by the force F of the pressure surface P of the blade 22,
thereby suppressing the development of the boundary layer 35. On
the suction surface S of the blade 22, the boundary layer 35 is
pressed against the suction surface S by the centrifugal force F1,
thereby preventing its movement toward the shroud 21 and thus
suppressing the development of the boundary layer 35.
[0043] Furthermore, in the flow direction of the fluid, the blade
22 is formed in such a manner that the inclination angle
.gamma..theta. is gradually decreasing from the leading edge 22A
toward the trailing edge 22B. Consequently, the surface area of the
blade 22 in the latter half of the blade 22 is reduced, and thus
the amount of the boundary layer developed over the blade surface
in the latter half of the blade 22 can be reduced. This can
suppress the generation of the energy deficit portion on the blade
outlet side, thereby allowing the performance of the impeller 6 to
be fulfilled sufficiently.
[0044] Moreover, the inclination angle .gamma..theta. of the
trailing edge 22B in the blade 22 is zero or positive over the
region from the hub 20 side to the shroud 21 side according to the
present embodiment. Thus, the height (length) of the trailing edge
22B of the blade 22 in the direction of the axis line L can be made
the shortest distance. Consequently, the amount of the wake flow
due to the thickness of the trailing edge 22B of the blade 22 can
be minimized. Furthermore, the reduced surface area of the blade 22
in the latter half of the blade 22 can significantly reduce the
amount of the boundary layer developed over the blade surface in
the latter half of the blade 22 as compared to the conventional
technique.
[0045] Moreover, the provision of the above-described impeller 6 in
the centrifugal compressor 1 of the present embodiment can suppress
the generation of the energy deficit portion on the outlet side of
the blade 22, thus improving the compression efficiency of the
centrifugal compressor 1.
[0046] While the embodiment of the present invention has been
described above, the present invention is not limited by the above
details. For example, the above-described embodiment has described
the configuration in which the inclination angle .gamma..theta. of
the trailing edge 22B in the blade 22 is zero or positive over a
region from the hub 20 side to the shroud 21 side. However, the
inclination angle .gamma..theta. of the trailing edge in the blade
22 may be zero or positive on the hub 20 side and may be gradually
increasing toward the shroud 21. According to such a configuration,
the pressure surface P of the blade 22 faces the inner wall surface
21A of the shroud 21 also in the latter half of the blade 22.
Consequently, the boundary layer 35 is pressed against the shroud
21 by the force of the pressure surface P of the blade 22, thereby
suppressing the development of the boundary layer 35 more
effectively.
[0047] Moreover, the leading edge 22A of the blade 22, when
projected onto the meridional cross section, has the shape in which
the hub 20 and the shroud 21 are generally straight lines in the
above-described embodiment. However, the present invention is not
limited thereto. The leading edge 22A may have a protruding shape
protruded toward the upstream side in the flow direction of the
fluid between the hub 20 and the shroud 21. According to such a
configuration, the area of a portion of the leading edge 22A of the
blade 22 facing the shroud 21 can be increased, thereby more
effectively suppressing the development of the boundary layer 35
accordingly.
[0048] Moreover, while the leading edge of the blade 22 in the
present embodiment is configured such that the inclination angle
.gamma..theta. curves with a gradually larger degree from the hub
20 side toward the shroud 21, the present invention is not limited
thereto. The inclination may be configured to increase (bend)
sharply so as to turn outwardly (configuration provided with a
discontinuous portion somewhere in the span direction). In this
case, not a single but a plurality of bent portions (discontinuous
portions) may be provided.
[0049] Moreover, while the impeller 6 in the present embodiment is
provided in the two-stage centrifugal compressor 1, the impeller 6
can be applied to a single-stage centrifugal compressor or a
multistage centrifugal compressor including three or more stages as
long as the compressor includes an impeller.
REFERENCE SIGNS LIST
[0050] 1 centrifugal compressor [0051] 2 casing [0052] 5 rotary
shaft [0053] 6 impeller (rotary impeller) [0054] 6A intake port
[0055] 6B blowoff port [0056] 10 suction port [0057] 10A suction
space [0058] 11 intake passage [0059] 12 vaneless diffuser [0060]
14 return bend [0061] 15 return vane [0062] 16 scroll [0063] 17
discharge port [0064] 18 balance piston [0065] 20 hub [0066] 20A
inner wall surface [0067] 21 shroud [0068] 21A inner wall surface
[0069] 22 blade [0070] 22A leading edge [0071] 22B trailing edge
[0072] 30 meridional cross section [0073] 32 camber line [0074] 33
projection line [0075] 35 boundary layer (a portion with a
particularly large pressure loss in an accumulated development
portion of the boundary layer) [0076] 100 blade [0077] 101 intake
port [0078] 102 leading edge [0079] 103 camber line [0080] 104
straight line [0081] 105 wall surface [0082] 106 wall surface
[0083] 107 blowoff port [0084] 108 trailing edge [0085] 109
boundary layer (a portion with a particularly large pressure loss
in an accumulated development portion of the boundary layer) [0086]
L axis line [0087] O origin point [0088] P pressure surface [0089]
S suction surface [0090] Z' parallel line [0091] r straight line
[0092] .gamma..theta. inclination angle
* * * * *