U.S. patent application number 13/522704 was filed with the patent office on 2012-11-22 for non-periodic centrifugal compressor diffuser.
This patent application is currently assigned to CAMERON INTERNATIONAL CORPORATION. Invention is credited to Mikhail Grigoriev, James Hitt, Chester V. Swiatek.
Application Number | 20120294711 13/522704 |
Document ID | / |
Family ID | 43920664 |
Filed Date | 2012-11-22 |
United States Patent
Application |
20120294711 |
Kind Code |
A1 |
Grigoriev; Mikhail ; et
al. |
November 22, 2012 |
NON-PERIODIC CENTRIFUGAL COMPRESSOR DIFFUSER
Abstract
A system, in certain embodiments, includes a centrifugal
compressor diffuser having a mounting surface and plurality of
diffuser vanes extending from the mounting surface in an axial
direction and forming an asymmetrical (e.g., non-periodic) pattern
around the circumference of the diffuser. The asymmetrical pattern
may be determined based upon characteristics of fluid flowing from
an impeller across the diffuser and through a scroll of a
centrifugal compressor.
Inventors: |
Grigoriev; Mikhail; (East
Amherst, NY) ; Swiatek; Chester V.; (Amherst, NY)
; Hitt; James; (Lancaster, NY) |
Assignee: |
CAMERON INTERNATIONAL
CORPORATION
Houston
TX
|
Family ID: |
43920664 |
Appl. No.: |
13/522704 |
Filed: |
November 30, 2010 |
PCT Filed: |
November 30, 2010 |
PCT NO: |
PCT/US10/58439 |
371 Date: |
July 17, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61301580 |
Feb 4, 2010 |
|
|
|
Current U.S.
Class: |
415/204 |
Current CPC
Class: |
F05D 2250/52 20130101;
F04D 29/444 20130101; F04D 29/666 20130101 |
Class at
Publication: |
415/204 |
International
Class: |
F04D 29/44 20060101
F04D029/44 |
Claims
1. A system, comprising: a centrifugal gas compressor, comprising:
an impeller; a diffuser configured to convert velocity into
pressure for a fluid flow from the impeller; and a scroll
configured to direct the fluid flow from the diffuser out of the
centrifugal gas compressor; wherein the diffuser comprises a
plurality of diffuser vanes arranged in an asymmetrical pattern
around a mounting surface of the diffuser.
2. The system of claim 1, wherein the asymmetrical pattern is
determined based upon characteristics of the fluid flowing from the
impeller across the diffuser and through the scroll.
3. The system of claim 1, wherein the asymmetrical pattern
comprises an asymmetrical geometry.
4. The system of claim 3, wherein the asymmetrical geometry
comprises a change in a pressure surface from a first diffuser vane
to a second diffuser vane.
5. The system of claim 3, wherein the asymmetrical geometry
comprises a change in a suction surface from a first diffuser vane
to a second diffuser vane.
6. The system of claim 1, wherein the asymmetrical pattern
comprises an asymmetrical orientation.
7. The system of claim 6, wherein the asymmetrical orientation
comprises a change in radial location from a first diffuser vane to
a second diffuser vane.
8. The system of claim 6, wherein the asymmetrical orientation
comprises a change in circumferential location with respect to
equally spaced reference points from a first diffuser vane to a
second diffuser vane.
9. The system of claim 6, wherein the asymmetrical orientation
comprises a change in angular orientation from a first diffuser
vane to a second diffuser vane.
10. A system, comprising: a centrifugal compressor diffuser having
a mounting surface and a plurality of diffuser vanes extending from
the mounting surface in an axial direction and forming an
asymmetrical pattern in a circumferential direction along the
mounting surface.
11. The system of claim 10, wherein the asymmetrical pattern
comprises an asymmetrical geometry.
12. The system of claim 11, wherein the asymmetrical geometry
comprises a change in a pressure surface or a suction surface from
a first diffuser vane to a second diffuser vane.
13. The system of claim 10, wherein the asymmetrical pattern
comprises an asymmetrical orientation.
14. The system of claim 13, wherein the asymmetrical orientation
comprises a change in radial location from a first diffuser vane to
a second diffuser vane.
15. The system of claim 13, wherein the asymmetrical orientation
comprises a change in circumferential location with respect to
equally spaced reference points from a first diffuser vane to a
second diffuser vane.
16. The system of claim 13, wherein the asymmetrical orientation
comprises a change in angular orientation from a first diffuser
vane to a second diffuser vane.
17. A method, comprising: determining three-dimensional flow field
characteristics of a fluid flowing from a centrifugal compressor
impeller across a centrifugal compressor diffuser and through a
centrifugal compressor scroll; and optimizing the shape,
orientation, and location of each of a plurality of diffuser vanes
of the centrifugal compressor diffuser based on the
three-dimensional flow field characteristics.
18. The method of claim 17, wherein optimizing the shape,
orientation, and location of each of the plurality of diffuser
vanes comprises minimizing the creation of loss-producing fluid
structures near each of the plurality of diffuser vanes.
19. The method of claim 18, wherein optimizing the shape,
orientation, and location of each of the plurality of diffuser
vanes comprises optimizing a pressure surface or a suction surface
of each of the plurality of diffuser vanes.
20. The method of claim 17, wherein one or more diffuser vane
surfaces are not spatially symmetric along equally spaced radial
lines defined at an angle equal to 360 degrees divided by the
number of diffuser vanes.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to U.S. Provisional Patent
Application No. 61/301,580, entitled "Non-Periodic Centrifugal
Compressor Diffuser", filed on Feb. 4, 2010, which is herein
incorporated by reference in its entirety.
BACKGROUND
[0002] This section is intended to introduce the reader to various
aspects of art that may be related to various aspects of the
present invention, which are described and/or claimed below. This
discussion is believed to be helpful in providing the reader with
background information to facilitate a better understanding of the
various aspects of the present invention. Accordingly, it should be
understood that these statements are to be read in this light, and
not as admissions of prior art.
[0003] Centrifugal compressors may be employed to provide a
pressurized flow of fluid for various applications. Such
compressors typically include an impeller that is driven to rotate
by an electric motor, an internal combustion engine, or another
drive unit configured to provide a rotational output. As the
impeller rotates, fluid entering in an axial direction is
accelerated and expelled in a circumferential and a radial
direction. The high-velocity fluid then crosses a diffuser, which
converts the velocity head of the fluid into a pressure head (i.e.,
decreases flow velocity and increases flow pressure). The volute or
scroll then collects the radially outward flow and directs it into
a pipe. In this manner, the centrifugal compressor produces a
high-pressure fluid output. The overall stage efficiency is a
product of how effectively these three components (e.g., the
impeller, the diffuser, and the volute or scroll) individually
perform as well as how they function together.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] Various features, aspects, and advantages of the present
invention will become better understood when the following detailed
description is read with reference to the accompanying figures in
which like characters represent like parts throughout the figures,
wherein:
[0005] FIG. 1 is an axial view of an exemplary embodiment of a
centrifugal compressor stage having an impeller, a non-periodic
diffuser, and a scroll;
[0006] FIG. 2 is a perspective view of an exemplary embodiment of a
centrifugal compressor stage having an impeller, a non-periodic
diffuser, and a scroll;
[0007] FIG. 3 is a perspective view of the impeller and the
non-periodic diffuser of the centrifugal compressor stage of FIGS.
1 and 2;
[0008] FIG. 4 is a perspective view of the impeller of FIGS. 1
through 3;
[0009] FIG. 5 is a side view of the impeller of FIGS. 1 through
3;
[0010] FIG. 6 is a perspective view of the non-periodic diffuser of
FIGS. 1 through 3;
[0011] FIG. 7 is a perspective view of a periodic diffuser;
[0012] FIG. 8 is a partial perspective view of the periodic
diffuser taken along line 8-8 of FIG. 7;
[0013] FIG. 9 is an axial view of the non-periodic diffuser of
FIGS. 1 through 3 and FIG. 6; and
[0014] FIG. 10 is a flow chart of a method for deriving geometries
and orientations of a plurality of diffuser vanes arranged in an
asymmetrical (e.g., non-periodic) pattern around the mounting
surface of the non-periodic diffuser.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
[0015] One or more specific embodiments of the present invention
will be described below. These described embodiments are only
exemplary of the present invention. Additionally, in an effort to
provide a concise description of these exemplary embodiments, all
features of an actual implementation may not be described in the
specification. It should be appreciated that in the development of
any such actual implementation, as in any engineering or design
project, numerous implementation-specific decisions must be made to
achieve the developers' specific goals, such as compliance with
system-related and business-related constraints, which may vary
from one implementation to another. Moreover, it should be
appreciated that such a development effort might be complex and
time consuming, but would nevertheless be a routine undertaking of
design, fabrication, and manufacture for those of ordinary skill
having the benefit of this disclosure.
[0016] Embodiments of the present disclosure include enhancements
in the design of radial diffusers (e.g., diffusers used in
centrifugal compressor systems). In particular, the disclosed
embodiments match the diffuser with an associated impeller and
scroll or volute. Diffusers in centrifugal compressor systems serve
a number of purposes. One of the primary functions of a diffuser is
to diffuse (e.g., slow down) compressed gas as it passes from an
exit of the impeller to the scroll or volute. Exactly how this is
accomplished may have a significant impact on the loss in
isentropic efficiency of the overall compressor stage.
[0017] Historically, diffuser design was based on a prediction of
average flow conditions exiting the impeller. It was further
assumed that there were no circumferential pressure distortions
imposed by the scroll and no localized pressure distortions caused
by the volute tongue. These assumptions are equivalent to assuming
that the flow leaving the diffuser enters a dump collector or a
vaneless return channel of a classical in-line compressor. In other
words, a uniform circumferential pressure distribution at the exit
of the diffuser was assumed. This assumption results in a diffuser
design that is periodic (e.g., circumferentially symmetric).
[0018] In the disclosed embodiments, the diffuser vanes are
arranged in an asymmetrical (e.g., non-periodic) pattern in a
circumferential direction around a mounting surface (e.g., a hub,
in this particular case) of the diffuser. Due at least in part to
the presence of the scroll or volute, the pressure distribution of
the fluid being compressed varies at different circumferential
locations around the mounting surface. Taking this varying pressure
distribution into consideration, the shape, orientation, and/or
location of the diffuser vanes may be varied to increase the
efficiency of the diffuser. In other words, each individual
diffuser vane may be specially designed based on the specific
pressure and flow characteristics near the diffuser vane.
[0019] FIG. 1 is an axial view and FIG. 2 is a perspective view of
an exemplary embodiment of a centrifugal compressor stage 10 having
an impeller 12, a non-periodic diffuser 14, and a scroll 16. The
centrifugal compressor stage 10 may be employed to provide a
pressurized flow of fluid for various applications. The impeller 12
may be driven to rotate by an electric motor, an internal
combustion engine, or another drive unit configured to provide a
rotational output. As the impeller 12 rotates, fluid entering in an
axial direction is accelerated and expelled in a circumferential
and a radial direction. The high-velocity fluid then crosses the
diffuser 14, which converts the velocity head of the fluid into a
pressure head (i.e., decreases flow velocity and increases flow
pressure). The scroll (or volute) 16 then collects the radially
outward flow and directs it into a pipe, for example. In this
manner, the centrifugal compressor stage 10 produces a
high-pressure fluid output. The overall stage efficiency is a
product of how effectively these three components (e.g., the
impeller 12, the diffuser 14, and the scroll 16) individually
perform as well as how they work together. For the purposes of this
analysis, volute and scroll are interchangeable names for the same
device that accepts radial flow, may or may not further diffuse the
flow, and then directs the flow to an exit pipe.
[0020] The scroll 16 may distort the flow field in the diffuser 14
and, in some cases, the circumferential distortion caused by the
scroll 16 may be measured at the exit of the impeller 12. The
pressure distortion imposed by the scroll 16, is generally
variable. In particular, the scroll 16 may typically operate in one
of three flow regions (e.g., neutral, accelerating flow, and
decelerating flow). The region within which the scroll 16 is
operating is determined by the specific application of the
centrifugal compressor stage 10. In an application with a
relatively high flow rate, the average flow in the scroll 16 will
be accelerating as it approaches a tongue of the scroll 16. This
imposes a circumferential pressure distortion on the diffuser 14.
Conversely, in a lower flow application, the flow in the scroll 16
is decelerating and imposes a circumferential pressure gradient in
the opposite direction of the accelerating flow. The degree of
distortion roughly correlates with how far the application is from
a neutral point. In every scroll or volute, there is an application
point where the flow in the scroll or volute is neither
accelerating nor decelerating (e.g., diffusing). Even at this
neutral point, the tongue of the scroll 16 may impose pressure and
flow field distortions that affect a region of the diffuser 14, but
do not extend a full 360 degrees around the diffuser 14
circumferentially. This localized region of flow distortion may
extend from the tongue region to an exit of the impeller 12.
[0021] FIG. 3 is a perspective view of the impeller 12 and the
non-periodic diffuser 14 of the centrifugal compressor stage 10 of
FIGS. 1 and 2. As illustrated, the impeller 12 has multiple blades
18. As the impeller 12 is driven to rotate by an external source
(e.g., electric motor, internal combustion engine, etc.),
compressible fluid crossing the blades 18 is accelerated toward the
diffuser 14 disposed radially about the impeller 12. As illustrated
in FIGS. 1 and 2, the scroll 16 is positioned directly adjacent to
the diffuser 14, and serves to collect the fluid flow leaving the
diffuser 14. The diffuser 14 is configured to convert the
high-velocity fluid flow from the impeller 12 into a high-pressure
flow (e.g., convert the dynamic head to pressure head).
[0022] In the present embodiments, the diffuser 14 includes
diffuser vanes 20 coupled to a mounting surface 22 (e.g., a hub, in
this particular case) of the diffuser 14 in an asymmetrical (e.g.,
non-periodic) annular configuration in a circumferential direction
31 around the mounting surface 22. The diffuser vanes 20 are
configured to increase diffuser efficiency. As described below,
each diffuser vane 20 includes a leading edge section 42 and a
trailing edge section 46. In addition, each diffuser vane 20
includes a pressure surface 50 and a suction surface 52 extending
from the leading edge section 42 to the trailing edge section 46 on
opposite sides of the diffuser vane 20. By designing each
individual diffuser vane 20 based on the specific pressure and flow
characteristics near the diffuser vane 20, the efficiency of the
diffuser 14 may be increased as compared to conventional, periodic
(e.g., symmetrical) diffusers.
[0023] FIG. 4 is a perspective view and FIG. 5 is a side view of
the impeller 12 of FIGS. 1 through 3. As illustrated in FIG. 5, a
flow 24 of a compressible fluid may be directed to the impeller 12
opposite to an axial direction 26. In other words, the flow 24 of
compressible fluid may be directed to the impeller 12 along a
common central axis of the impeller 12, diffuser 14, and scroll 16.
As described above, as the impeller 12 rotates, the fluid entering
in the axial direction 26 is accelerated and expelled in a
circumferential and a radial direction. More specifically, as
illustrated in FIG. 5, a flow 28 of accelerated fluid may be
directed at least partially in a radial direction 30. The radial
direction 30 of the impeller 12 may be any direction perpendicular
to the axial direction 26, which coincides (in both location and
direction) with the common central axis of the impeller 12,
diffuser 14, and scroll 16. In addition, the accelerated fluid may
be directed at least partially in a circumferential direction 31,
which may be any rotational direction around the common central
axis of the impeller 12, diffuser 14, and scroll 16.
[0024] FIG. 6 is a perspective view of the non-periodic diffuser 14
of FIGS. 1 through 3. As illustrated, the diffuser 14 shares a
common central axis in an axial direction 26 with the impeller 12
of FIGS. 4 and 5. In addition, the radial direction 30 with respect
to the diffuser 14 is the same as the impeller 12. In other words,
the radial direction 30 of the diffuser 14 may be any direction
perpendicular to the axial direction 26, which coincides (in both
location and direction) with the common central axis of the
impeller 12, diffuser 14, and scroll 16. In addition, as described
above, the diffuser 14 includes diffuser vanes 20 arranged in an
asymmetrical pattern in a circumferential direction 31 around the
mounting surface 22 of the diffuser 14. In other words, the shape,
orientation, and/or location of the diffuser vanes 20 are
non-periodic (e.g., asymmetrical) from one diffuser vane 20 to the
next diffuser vane 20. The circumferential direction 31 of the
diffuser 14 may be any rotational direction around the common
central axis of the impeller 12, diffuser 14, and scroll 16.
[0025] To illustrate the non-periodic design of the diffuser vanes
20 of the non-periodic diffuser 14, the non-periodic diffuser 14
will be compared to a diffuser having substantially identical
diffuser vanes in a symmetrical (e.g., periodic) pattern in a
circumferential direction 31 around a mounting surface of the
diffuser. For example, FIG. 7 is a perspective view of a periodic
diffuser 32. In addition, FIG. 8 is a partial perspective view of
the periodic diffuser 32 taken along line 8-8 of FIG. 7. As
illustrated in FIG. 7, the periodic diffuser 32 includes a
plurality of substantially identical diffuser vanes 34 disposed in
a symmetrical (e.g., periodic) pattern in a circumferential
direction 31 around a mounting surface 36 (e.g., a hub, in this
particular case) of the periodic diffuser 32.
[0026] FIG. 8 illustrates a single diffuser vane 34 of the periodic
diffuser 32, which will be used as a reference vane. For any given
axial height z of each diffuser vane 34, a reference surface 38 may
be defined along a reference plane whose normal coincides with the
axial direction 26. In the reference diffuser vane 34 of FIG. 8,
the reference surface 38 is defined by an outer surface of the
diffuser vane 34. However, the analysis described herein may be
utilized for any axial height of the diffuser vane 34. In other
words, the reference plane may be defined at any axial height of
the diffuser vanes 34. In the illustrated example, the reference
plane includes the reference center point z.sub.ref, which passes
through the common central axis of the impeller 12, diffuser 14,
and scroll 16.
[0027] The reference surface 38 may be characterized by a
collection of unique points defined by a radial distance r from the
reference center point z.sub.ref, an angular location .theta., and
an axial height z. For any given reference plane, the axial height
z for the collection of unique points will be the same. However,
the radial distance r and the angular location .theta. will be
different and will define each unique point of the reference
surface 38 in the reference plane. For example, a leading edge
point 40 corresponding to the leading edge section 42 of the
diffuser vane 34 may be defined as a baseline point of the
reference surface 38 and, as such, may be defined by a radial
distance r.sub.0 and an angular location .theta..sub.0 equal to 0
degrees. Similarly, a trailing edge point 44 corresponding to the
trailing edge section 46 of the diffuser vane 34 may be defined by
a radial distance r.sub.1 and an angular location .theta..sub.1. In
addition, a pressure surface point 48 may be defined by a radial
distance r.sub.2 and an angular location .theta..sub.2. As such, a
pressure surface 50 of the diffuser vane 34 may be defined by the
plurality of points along the pressure surface 50 of the diffuser
vane 34. However, a suction surface 52 of the diffuser vane 34 may
be similarly defined. Indeed, there may be an infinite number of
unique points in the reference surface 38 of the reference diffuser
vane 34 illustrated in FIG. 8. However, the number of unique points
used to define the design of the individual diffuser vanes 34 may
be limited to facilitate computation of the shape, orientation,
and/or location of the diffuser vanes 34.
[0028] Furthermore, each of the diffuser vanes 34 of the diffuser
32 of FIG. 7 may similarly include a collection of unique points
along the reference plane. In other words, each of the diffuser
vanes 34 may include a two-dimensional area defined by a collection
of unique points along the reference plane, such as the reference
surface 38 of the reference diffuser vane 34 illustrated in FIG. 8.
For the periodic diffuser 32 of FIGS. 7 and 8, for every point that
lies within the two-dimensional domain in the reference plane
(e.g., the reference surface 38) for the reference diffuser vane
34, the rotation of each of these points by an integer multiple of
360.0 divided by N will yield a point that lies within a
two-dimensional domain in the reference plane for another diffuser
vane 34, where N is the number of diffuser vanes 34 of the diffuser
32. For example, the diffuser 32 illustrated in FIG. 7 includes
nine diffuser vanes 34. As such, for every point that lies within
the two-dimensional domain in the reference plane (e.g., the
reference surface 38) for the reference diffuser vane 34, the
rotation of the point by 40 degrees, 80 degrees, 120 degrees, 160
degrees, 200 degrees, 240 degrees, 280 degrees, and 320 degrees
(e.g., integer multiples of 360.0 degrees divided by nine, or 40.0
degrees) yields a point that lies within the two-dimensional domain
in the reference plane for another diffuser vane 34.
[0029] In contrast, any diffuser that does not meet this
requirement is considered to be non-periodic. For example, FIG. 9
is an axial view of the non-periodic diffuser 14 of FIGS. 1 through
3 and FIG. 6 having a plurality of diffuser vanes 54, 56, 58, 60,
62, 64, 66, 68, and 70 arranged in a non-periodic (e.g., an
asymmetrical) pattern around a circumferential direction 31 of the
mounting surface 22. To illustrate the nature of the non-periodic
(e.g., an asymmetrical) pattern illustrated in FIG. 9, reference
points A, B, C, D, E, F, G, H, and I are located at equally spaced
circumferential locations around the mounting surface 22. As
illustrated, the diffuser 14 of FIG. 9 includes nine diffuser vanes
20. As such, the reference points A, B, C, D, E, F, G, H, and I are
equally spaced at arc angles .phi. of 40 degrees (e.g., 360.0
degrees divided by nine).
[0030] Each of the illustrated diffuser vanes 54, 56, 58, 60, 62,
64, 66, 68, and 70 are generally associated with one of the
reference points A, B, C, D, E, F, G, H, and I (e.g., diffuser vane
54 with reference point A, diffuser vane 56 with reference point B,
diffuser vane 58 with reference point C, diffuser vane 60 with
reference point D, diffuser vane 62 with reference point E,
diffuser vane 64 with reference point F, diffuser vane 66 with
reference point G, diffuser vane 68 with reference point H, and
diffuser vane 70 with reference point I). The reference points A,
B, C, D, E, F, G, H, and I are used to illustrate how the shape,
orientation, and/or location of the diffuser vanes 54, 56, 58, 60,
62, 64, 66, 68, and 70 may change from diffuser vane to diffuser
vane along a circumferential direction 31 of the mounting surface
22.
[0031] More specifically, as described above, in order to be
considered a periodic (e.g., symmetrical) diffuser 14, for every
point that lies within the two-dimensional domain for diffuser vane
54 (e.g., a reference vane) in a reference plane for diffuser vane
54, the rotation of the point by 40 degrees, 80 degrees, 120
degrees, 160 degrees, 200 degrees, 240 degrees, 280 degrees, and
320 degrees (e.g., integer multiples of 360.0 degrees divided by
nine, or 40.0 degrees) would yield a point that lies within the
two-dimensional domain in the reference plane for the other
diffuser vanes 56, 58, 60, 62, 64, 66, 68, and 70. However, as
illustrated, reference points B, C, D, E, F, G, H, and I, which
correspond to reference point A rotated through arc angles of 40
degrees, 80 degrees, 120 degrees, 160 degrees, 200 degrees, 240
degrees, 280 degrees, and 320 degrees, do not all lie within the
two-dimensional domain in the reference plane for the other
diffuser vanes 56, 58, 60, 62, 64, 66, 68, and 70. For example,
reference points E, F, G, H, and I do not lie within the
two-dimensional domain in the reference plane for diffuser vanes
62, 64, 66, 68, and 70. As such, the diffuser 14 illustrated in
FIG. 9 is a non-periodic (e.g., asymmetrical) diffuser 14.
[0032] As described above, the asymmetrical (e.g., non-periodic)
pattern of diffuser vanes 20 in a circumferential direction 31
around the mounting surface 22 may be determined by taking into
consideration pressure and fluid flow characteristics of a fluid
flowing from the impeller 12 across the diffuser 14 and through the
scroll 16. For example, FIG. 10 is a flow chart of a method 72 for
deriving the shape, orientation, and/or location of a plurality of
diffuser vanes 20 arranged in an asymmetrical (e.g., non-periodic)
pattern around the mounting surface 22 of the non-periodic diffuser
14. Pressure and fluid flow characteristics of the fluid being
compressed by the centrifugal compressor stage 10 may be determined
across the entire impeller-diffuser-scroll set (e.g., from the
impeller 12 across the diffuser 14 and through the scroll 16) such
that perturbations of the flow field may be taken into
consideration when deriving the shape, orientation, and/or location
of each individual diffuser vane 20 of the diffuser 14 (block 74).
More specifically, the pressure and fluid flow characteristics
across the entire impeller-diffuser-scroll set may be used to
derive the shape, orientation, and/or location of each individual
diffuser vane 20 of the diffuser 14 such that at least one of the
diffuser vanes 20 is not derived by simply performing a theoretical
rotation of each of the other diffuser vanes 20 through an arc
angle equal to an integer multiple of 360.0 degrees divided by N,
where N is equal to the number of diffuser vanes 20 of the diffuser
14 (block 76). Moreover, in certain embodiments, by taking the
pressure and fluid flow characteristics across the entire
impeller-diffuser-scroll set into consideration, an optimal number
of diffuser vanes 20 may be determined for the diffuser 14. The
method 72 of FIG. 10 may be executed on a computer specifically
programmed to derive the shape, orientation, and/or location of the
diffuser vanes 20. The computer may be any suitable computer (e.g.,
a laptop, desktop, server, and so forth) including one or more
processors that may communicate with a memory and execute computer
instructions such as those illustrated by the method 72 of FIG.
10.
[0033] Deriving the shape, orientation, and/or location of each of
the individual diffuser vanes 20 based on pressure and fluid flow
characteristics across the entire impeller-diffuser-scroll set may
enable adjustments of the diffuser vanes 20, which may reduce
adverse affects of perturbations of the flow field due, for
example, to the presence of the tongue of the volute or scroll. As
such, the non-periodic diffuser 14 may lead to overall efficiency
gains of its respective centrifugal compressor stage 10. For
example, in certain embodiments, deriving an asymmetrical (e.g.,
non-periodic) pattern of diffuser vanes 20 that takes variations of
the fluid flow field into consideration may lead to compressor
stage efficiency increases of approximately 0.5%, 1.0%, 1.5%, or
even more.
[0034] The asymmetrical (e.g., non-periodic) pattern of diffuser
vanes 20 may include an asymmetrical geometry, an asymmetrical
orientation, or both from a first diffuser vane 20 to a second
diffuser vane 20. For example, in certain embodiments, an
asymmetrical geometry may include a change in the pressure surface
50 from a first diffuser vane 20 to a second diffuser vane 20.
However, in other embodiments, an asymmetrical geometry may include
a change in the suction surface 52 from a first diffuser vane 20 to
a second diffuser vane 20. In addition, in certain embodiments, an
asymmetrical orientation may include a change in radial location
from a first diffuser vane 20 to a second diffuser vane 20.
However, in other embodiments, an asymmetrical orientation may
include a change in circumferential location with respect to
equally spaced reference points from a first diffuser vane 20 to a
second diffuser vane 20. Moreover, in other embodiments, an
asymmetrical orientation may include a change in angular
orientation from a first diffuser vane 20 to a second diffuser vane
20.
[0035] Uniquely different in this approach is the use of
time-unsteady computational flow dynamics (CFD) analysis to
optimize the performance of the non-periodic diffuser 14 at each
individual diffuser vane 20 with the computational field extending
from upstream of the impeller 12 to downstream of the scroll 16.
The result of this level of analysis enables a comprehensive view
of the non-steady flow field in the diffuser 14 and an overall
estimate of the performance of the compressor stage 10 with the
diffuser 14. The optimum design of the diffuser vanes 20 minimizes
the creation of loss-producing fluid structures near the diffuser
vanes 20. In the disclosed embodiments, the optimum shape,
orientation, and/or location for the individual diffuser vanes 20
results in one or more of the diffuser vanes 20 no longer being
spatially symmetric along equally spaced radial lines defined at
arc angles equal to 360.0 degrees divided by the number of diffuser
vanes 20.
[0036] The individual diffuser vanes 20 may include transformed
two-dimensional cascade, three-dimensional sculpted flat plate
designs, three-dimensional twisted airfoils, or arbitrary
three-dimensional surfaces, for example. The exit flow field of the
impeller 12 and the exact volute geometry will determine the
optimum diffuser vane surface shapes. Each individual diffuser vane
20 may be specially designed based on the specific local pressure
and fluid flow characteristics imposed by both the impeller 12 and
the scroll 16. The final design will share one common
characteristic across all applications; namely, the diffuser 14
will be non-periodic (not circumferentially symmetric) because the
diffuser vanes 20 are locally optimized. In many cases, for any
given diffuser vane 20, there may be no single best unique diffuser
vane shape, and the optimum choice may be the simplest to
manufacture that also provides optimum performance. The benefit of
this design approach enables an improvement in overall stage
efficiency in the range of approximately 1.5% and also improvement
in stall margin.
[0037] While the invention may be susceptible to various
modifications and alternative forms, specific embodiments have been
shown by way of example in the drawings and have been described in
detail herein. However, it should be understood that the invention
is not intended to be limited to the particular forms disclosed.
Rather, the invention is to cover all modifications, equivalents,
and alternatives falling within the spirit and scope of the
invention as defined by the following appended claims.
* * * * *