CROSS-REFERENCE TO RELATED APPLICATION
Benefit is claimed of U.S. Patent Application No. 62/642,827, filed March
5 14, 2018, and entitled “Centrifugal Compressor Open Impeller”, the disclosure of
which is incorporated by reference herein in its entirety as if set forth at length.
BACKGROUND
The disclosure relates to centrifugal compressors. More particularly, the
10 disclosure relates to centrifugal compressor impeller configurations.
Centrifugal compressors are often used in vapor compression systems (e.g.,
refrigeration). Several considerations go into impeller design and other aspects of
compressor design.
Impellers are broadly characterized in two groups: open or unshrouded
15 impellers; and shrouded impellers. Both groups form the impeller with a hub and
vanes (also termed “blades”) extending outward from the hub. The hub outer
surface extends from an upstream end or nose (axial inlet) axially and then radially
outward to a downstream end (radial outlet). Accordingly, the vanes, near the
upstream end protrude generally radially outward from the hub and toward the
20 downstream end protrude axially from the hub.
With a shrouded impeller, an integral shroud surrounds the vanes so that
the vanes extend across a flowpath between the surface of the hub and a surface of
the shroud. Exemplary shrouded impellers are unitarily formed via casting and
machining of an alloy. The shroud greatly rigidifies the vanes and reduces
25 tendencies toward vibration. This may allow use of a relatively thinner vane
structure than in an equivalent open impeller wherein the vanes are secured only at
the hub.
In an open impeller situation, edges of the vanes closely interface with a
separate shroud on the compressor. There may be position control between the
30 impeller and shroud to balance loss of efficiency due to leakage against risk of
damage from impeller-to-shroud contact.
2
Open impellers offer certain ease of manufacture considerations. For
example, the vanes may be easily machined (either entirely or finish machining of
cast-in vanes). Open impellers also allow tailoring of blade geometry for particular
end uses. For example, one basic impeller casting may have its blades machined
5 differently (e.g., to different heights) for different compressor models or
submodels.
Additionally, several compressor drive configurations are used with
centrifugal compressors. In direct drive compressors, the impeller is mounted to a
motor shaft. In geared compressors, a transmission intervenes between the motor
10 and the impeller. For example, a geared reduction may have a large gear on the
motor shaft mating with a small gear on the impeller shaft. This may be used in
large capacity compressor situations wherein impeller rotational speed is low.
Yet other variations include multi-impeller compressors.
15 SUMMARY
One aspect of the disclosure involves a centrifugal compressor impeller
comprising a hub having a gaspath surface extending from a leading end to a
trailing end. A plurality of blades extend from the hub gaspath surface and each
have: a leading edge; a trailing edge; a first face; a second face; and a tip. A
20 plurality of flow splitter segments extend between associated twos of the blades.
Each flow splitter segment is spaced from both the hub gaspath surface and the tips
of the associated two blades.
In one or more embodiments of any of the foregoing embodiments, the
plurality of flow splitter segments is within an upstream third or a downstream
25 third of a flowpath length from the leading edges to the trailing edges.
In one or more embodiments of any of the foregoing embodiments, the
plurality of flow splitter segments is a first plurality of flow splitter segments and
the impeller further comprises a second plurality of flow splitter segments
extending between the blades and spaced from both the hub gaspath surface and
30 the tips of the blades.
3
In one or more embodiments of any of the foregoing embodiments, the first
plurality of flow splitter segments is within an upstream third of a flowpath length
from the leading edges to the trailing edges and the second plurality of flow splitter
segments is within a downstream third of said flowpath length from the leading
5 edges to the trailing edges.
In one or more embodiments of any of the foregoing embodiments, the
plurality of blades is a first plurality of blades. A second plurality of blades extend
from the hub gaspath surface and each have: a leading edge; a trailing edge; a first
face; a second face; and a tip. Said leading edges of the second plurality of blades
10 are downstream recessed relative to the leading edges of the first plurality of
blades. The plurality of flow splitter segments is upstream of the leading edges of
the second plurality of blades.
In one or more embodiments of any of the foregoing embodiments, the
plurality of flow splitter segments is a first plurality of flow splitter segments and
15 the impeller further comprises a second plurality of flow splitter segments
extending between the blades of the first plurality of blades and the second plurality
of blades and spaced from both the hub gaspath surface and the tips of the first
plurality of blades and the second plurality of blades.
In one or more embodiments of any of the foregoing embodiments, the hub,
20 the plurality of blades, and the plurality of flow splitter segments are formed as a
unitary monolithic metallic casting.
In one or more embodiments of any of the foregoing embodiments, the
plurality of flow splitter segments forms a circumferential ring.
In one or more embodiments of any of the foregoing embodiments, the hub
25 and the plurality of blades are formed as a first unitary metallic casting and the
circumferential ring is formed separately formed from said first unitary metallic
casting.
In one or more embodiments of any of the foregoing embodiments, the hub
and the plurality of blades comprise a first alloy and the circumferential ring
30 comprises a second alloy different from the first alloy.
4
In one or more embodiments of any of the foregoing embodiments, the first
alloy is an aluminum alloy; and the second alloy is a titanium alloy.
In one or more embodiments of any of the foregoing embodiments, the hub,
the plurality of blades, and the plurality of flow splitter segments are formed as a
5 unitary monolithic glass-filled nylon.
In one or more embodiments of any of the foregoing embodiments, the
impeller has an axial inlet and a radial outlet.
In one or more embodiments of any of the foregoing embodiments, the
impeller has an axial inlet and an axial outlet.
10 In one or more embodiments of any of the foregoing embodiments, a
compressor comprising the compressor impeller and further comprises a housing
having an inlet port and an outlet port; a motor mounted within the housing. Said
compressor impeller is coupled to the motor to be driven for rotation about an
impeller axis. A shroud faces the tips.
15 In one or more embodiments of any of the foregoing embodiments, a
method for using the compressor comprises running the motor to drive the
compressor impeller to drive a flow from the inlet to the outlet wherein at least
25% of the flow passes radially outboard of the plurality of flow splitter segments
and at least 25% of the flow passes radially inboard of the plurality of flow splitter
20 segments.
In one or more embodiments of any of the foregoing embodiments, a
method for manufacturing the compressor impeller comprises: forming the
plurality of flow splitter segments of a first alloy; and forming the plurality of
blades of a second alloy different from the first alloy.
25 In one or more embodiments of any of the foregoing embodiments, the
method for manufacturing comprises additive manufacture.
In one or more embodiments of any of the foregoing embodiments, the
method for manufacturing comprises additive manufacture of both the plurality of
flow splitter segments and the plurality of blades.
30 In one or more embodiments of any of the foregoing embodiments, a
method for manufacturing the compressor impeller comprises additive
5
manufacture of both the plurality of flow splitter segments and the plurality of
blades as a unit.
Another aspect of the disclosure involves a centrifugal compressor impeller
comprising a hub having a gaspath surface extending from a leading end to a
5 trailing end. A plurality of blades extend from the hub gaspath surface and each
have: a leading edge; a trailing edge; a first face; a second face; and a tip. A
circumferential ring extends between the blades and is spaced from both the hub
gaspath surface and the tips of the blades.
The details of one or more embodiments are set forth in the accompanying
10 drawings and the description below. Other features, objects, and advantages will
be apparent from the description and drawings, and from the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front view of a compressor.
15 FIG. 2 is a longitudinal section view of the compressor of FIG. 1 taken
along line 2-2.
FIG. 2A is an enlarged view of an impeller region of the compressor of
FIG. 2.
FIG. 3 is a front view of the impeller.
20 FIG. 4 is a partial axial sectional view of the impeller taken along line 4-4
of FIG. 3.
FIG. 5 is a partial side view of the impeller.
FIG. 6 is a central axial sectional view of a second impeller.
FIG. 7 is a partial transverse sectional view of a ring-to-vane intersection
25 on an impeller.
Like reference numbers and designations in the various drawings indicate
like elements.
6
DETAILED DESCRIPTION
FIG. 1 shows a compressor 20 having a housing or case (assembly) 22 with
an inlet or suction port 24 and an outlet or discharge port 26. A flowpath between
the suction port and discharge port may compress a vapor flow 400 (FIG. 2).
5 FIG. 2 shows the compressor 20 as including a motor 30 in a motor case
section of the housing. The motor has a stator 32 and a rotor 34. The rotor 34
includes a shaft 36 extending outward to mate with and drive a transmission 40.
The exemplary transmission 40 includes a driving gear 42 mated to the shaft 36 to
be driven about a shaft axis 502. The exemplary shaft 36 is supported by bearings
10 44, 46 for rotation about the axis 502. The transmission 40 further includes a driven
gear 50 mounted to an impeller shaft 52 held for rotation about an axis 500 by
bearings 54 and 56. An impeller 60 is mounted to a forward end portion of the
impeller shaft 52. The impeller has a hub 62 having an outboard surface (gaspath
surface) 64 (FIG. 2A) along a flowpath through the compressor. An inner diameter
15 (ID) surface of the impeller hub receives the impeller shaft 52.
The impeller 60 includes a plurality of vanes (also known as blades)
protruding from the surface 64. The exemplary impeller is configured with two sets
of interdigitated vanes 70A and 70B (FIG. 5). The exemplary vanes 70A are longer
along the flowpath with a leading edge 72A at the inlet end of the impeller. The
20 leading edges 72B of vanes 70B are recessed. Downstream or trailing edges 74A,
74B of the vanes may be at like position along the flowpath. In the illustrated
embodiment, the downstream edges extend axially along a radial outlet of the
impeller. The vanes have proximal or inboard boundaries at the surface 64 (FIG.
4) and extend to outboard or distal edges 78A, 78B serving as blade tips. The vanes
25 have opposite first surfaces (faces) 80A, 80B and second surfaces (faces) 82A, 82B
(FIG. 3). A vane height may be measured as the distance of the edge 78A, 78B
measured normal to the surface 64. An alternative parameter of vane height may
be the radial span of a vane at the inlet end or the axial span of the vane at the outlet
end.
30 FIG. 2 further shows a fixed shroud 90 and an inlet guide vane array 94
upstream thereof. The guide vanes may be rotated about their respective axes by
7
an actuator (e.g., servomotor or the like). Exemplary actuation involves a single
actuator moving all vanes in synchrony via geared or pulley interaction. FIG. 2
further shows a diffuser 100 having diffuser passageways 102 extending between
the impeller outlet and a discharge plenum 104 feeding the discharge port.
5 As so far described, the compressor is illustrative of one example of
numerous compressors to which the following teachings may be applied.
In FIG. 3, the illustrated impeller comprises a pair of rings 120, 122. The
exemplary rings are circumferential rings extending essentially exactly
circumferentially (e.g., not having an axial or radial spiral). The exemplary first
10 ring 120 is in an upstream third of the flowpath along the impeller spaced ahead of
the second vanes 70B so as to define segments between adjacent first vanes 70A.
The exemplary ring 120 has a generally rectangular central axial
cross-section (FIG. 4) extending from an upstream (leading) edge 130 (FIG. 5) to
a downstream (trailing) edge 132. The ring 120 and its segments thus also have an
15 inboard face or surface 134 (FIG. 4) and an outboard face or surface 136. The
inboard surface 136 faces and is relatively close to the hub gaspath surface 64.
Alternative cross-sections may be more arcuate to conform to bending of the
flowpath.
The second ring 122 is within a downstream third of the flowpath length
20 along the impeller. The exemplary second ring 122 also has a generally rectangular
cross-section having a leading edge 140 (FIG. 3), a trailing edge 142, an inboard
face 144 (FIG. 5), and an outboard face 146. The second ring 122 spans all vanes
(thus its segments each extend between one of the first vanes and one of the second
vanes).
25 By recessing the faces 136, 146 of the segments from the edges 78A, 78B,
the rings 120, 122 thus each split the flow through the impeller into an inboard
portion (between the surface 64 on the one hand and the faces 134 and 144 on the
other hand) and an outboard portion (between the shroud on the one hand and the
faces 136 and 146 on the other hand). An exemplary recessing may leave at least
30 10% of a vane height beyond the faces 136 and 146. Thus, the ring segments
8
alternatively may be described as flow splitter segments splitting the flow into
inboard and outboard portions.
The presence of the rings 120, 122 may limit resonant behavior of the
impeller in a desired speed range. This may have one or more of several
5 consequences including allowing thinner/lighter/more efficient vanes, allowing
higher speed operation, allowing reduction in other anti-vibration measures, and
improving service life.
The exemplary first ring 120 is shown recessed along the height of the
vanes 70A. This recessing allows machining of the edges 78A, 78B to select blade
10 height for a given application even while using one form of impeller precursor
(e.g., a raw casting with blade precursors or a machined casting with otherwise
fully functional blades already formed at a maximum height). Similarly, the ring
122 is radially recessed from the trailing edges 74A, 74B. This also allows radial
trimming of the impeller at the impeller outlet.
15 The compressor may be made using otherwise conventional or yetdeveloped
materials and techniques. A particular method for manufacturing the
integral rings is to sand cast, injection mold, or five axis mill. This may be of a
unitary single-alloy casting forming at least a portion of the hub along with the
vanes and ring(s). For example, some known impellers feature aluminum alloy cast
20 over a steel hub core/bushing.
Additive manufacturing techniques can be used. Additive manufacturing
may be used such as when the ring(s) are made out of a different material than are
the impeller hub and vanes (see FIG. 7). In one example, a multi-feed additive
manufacturing apparatus (e.g., fused deposition modeling (FDM) or the like) is
25 used with one feed for impeller hub and vane material and another for ring material.
Relative to hub/vane material, the ring material may be one or more of a more
expensive material, a stronger material, and a less machinable material. For
example, consider an aluminum alloy (e.g., majority Al by weight) for the
hub/vanes and a titanium alloy (e.g., majority Ti by weight) for the ring(s). In such
30 a process the ring alloy of each ring may form a continuous full annulus through
the vanes for hoop strength.
9
Alternative bimetallic manufacturing involves pre-forming the ring(s) such
as by machining and then over-casting the hub/vanes.
Yet alternative manufacture involves non-metallic materials. One example
is use of glass filled polymer such as a glass-filled polyamide (e.g., Nylon 12 GF).
5 Grades of Nylon 12 GF are commercially available for laser sintering manufacture
techniques. Thus, monolithic additive manufacture of the impeller including the
vanes and ring(s) by selective laser sintering (SLS) is a possible technique.
FIG. 6 shows an alternate impeller 160 for a mixed flow compressor
wherein the impeller has an axial inlet and an axial outlet. Despite the axial outlet,
10 the gaspath still substantially diverges radially from impeller inlet to impeller
outlet. Thus, exemplary gaspath outer diameter at the impeller outlet is still at least
about 130% of that at the impeller inlet and the median between the hub surface
and vane OD diverges more (e.g., median diameter at the outlet at least about 150%
of that at the inlet).
15 This particular example has rings formed of a different material than the
vanes, but unitary monolithic variants are also possible. The impeller has a hub 162
with a gaspath surface 164 and vanes 17 extending radially outward therefrom.
Two exemplary differences of the impeller 160 relative to the impeller 60 are the
axial outlet and the lack of two different lengths of vane 170. The vanes 170 thus
20 each have leading edge 172, trailing edge 174, outboard or distal edge 78, first
faces 80, and opposite second faces 82.
The use of “first”, “second”, and the like in the description and following
claims is for differentiation within the claim only and does not necessarily indicate
relative or absolute importance or temporal order. Similarly, the identification in a
25 claim of one element as “first” (or the like) does not preclude such “first” element
from identifying an element that is referred to as “second” (or the like) in another
claim or in the description.
One or more embodiments have been described. Nevertheless, it will be
understood that various modifications may be made. For example, when applied to
30 an existing basic system, details of such configuration or its associated use may
10
influence details of particular implementations. Accordingly, other embodiments
are within the scope of the following claims.

We Claim:
1. A centrifugal compressor impeller (60; 160) comprising:
a hub (62; 162) having a gaspath surface (64; 164) extending from a leading end to a trailing
end;
a plurality of blades (70A, 70B; 170) extending from the hub gaspath surface and each
having:
a leading edge (72A, 72B; 172);
a trailing edge (74A, 74B; 174);
a first face (80A, 80B; 180);
a second face (82A, 82B; 182); and
a tip (78A, 78B; 178); and
a plurality of flow splitter segments (120, 122; 320, 322) extending between associated twos
of the blades and each spaced from both the hub gaspath surface and the tips of the
associated two blades.
2. The compressor impeller (60; 160) of claim 1 wherein:
the plurality of flow splitter segments (120, 122; 320, 322) is within an upstream third or a
downstream third of a flowpath length from the leading edges to the trailing edges.
3. The compressor impeller (60; 160) of claim 1 wherein:
the plurality of flow splitter segments is a first plurality of flow splitter segments (120; 320)
and the impeller further comprises a second plurality of flow splitter segments (122; 320)
extending between the blades and spaced from both the hub gaspath surface and the tips
of the blades.
4. The compressor impeller (60; 160) of claim 3 wherein:
the first plurality of flow splitter segments (120; 320) is within an upstream third of a
flowpath length from the leading edges to the trailing edges; and
the second plurality of flow splitter segments (122; 322) is within a downstream third of said
flowpath length from the leading edges to the trailing edges.
12
5. The compressor impeller (60) of claim 1 wherein:
the plurality of blades is a first plurality of blades (70A);
a second plurality of blades 70B extending from the hub gaspath surface and each
have:
a leading edge;
a trailing edge;
a first face;
a second face; and
a tip;
said leading edges of the second plurality of blades are downstream recessed relative to the
leading edges of the first plurality of blades; and
the plurality of flow splitter segments is upstream of the leading edges of the second plurality
of blades.
6. The compressor impeller (60; 160) of claim 5 wherein:
the plurality of flow splitter segments is a first plurality of flow splitter segments and the
impeller further comprises a second plurality of flow splitter segments extending between
the blades of the first plurality of blades and the second plurality of blades and spaced
from both the hub gaspath surface and the tips of the first plurality of blades and the
second plurality of blades.
7. The compressor impeller (60; 160) of claim 1 wherein:
the hub, the plurality of blades, and the plurality of flow splitter segments are formed as a
unitary monolithic metallic casting.
8. The compressor impeller (60; 160) of claim 1 wherein:
the plurality of flow splitter segments forms a circumferential ring (120, 122; 320, 322).
9. The compressor impeller (60; 160) of claim 8 wherein:
the hub and the plurality of blades are formed as a first unitary metallic casting; and
13
the circumferential ring is formed separately formed from said first unitary metallic casting.
10. The compressor impeller (60; 160) of claim 8 wherein:
the hub and the plurality of blades comprise a first alloy; and
the circumferential ring comprises a second alloy different from the first alloy.
11. The compressor impeller (60; 160) of claim 10 wherein:
the first alloy is an aluminum alloy; and
the second alloy is a titanium alloy.
12. The compressor impeller (60; 160) of claim 1 wherein:
the hub, the plurality of blades, and the plurality of flow splitter segments are formed as a
unitary monolithic glass-filled nylon.
13. The compressor impeller (60) of claim 1 wherein:
5
the impeller has an axial inlet and a radial outlet.
14. The compressor impeller (160) of claim 1 wherein:
the impeller has an axial inlet and an axial outlet.
15. A compressor (20) comprising the compressor impeller (60; 160) of claim 1
and further comprising:
a housing (22) having an inlet port (24) and an outlet port (26);
a motor (30) mounted within the housing;
said compressor impeller coupled to the motor to be driven for rotation about an impeller
axis (500); and
a shroud (90) facing the tips.
16. A method for using the compressor of claim 15, the method comprising:
running the motor to drive the compressor impeller (60; 160) to drive a flow from the inlet to
the outlet wherein at least 25% of the flow passes radially outboard of the plurality of
14
5
flow splitter segments and at least 25% of the flow passes radially inboard of the plurality
of flow splitter segments.
17. A method for manufacturing the compressor impeller (60; 160) of claim 1, the
method comprising:
forming the plurality of flow splitter segments of a first alloy; and
forming the plurality of blades of a second alloy different from the first alloy.
18. The method of claim 17 comprising additive manufacture.
10 19. The method of claim 17 comprising additive manufacture of both the plurality
of flow splitter segments and the plurality of blades.
20. A method for manufacturing the compressor impeller (60; 160) of claim 1, the
method comprising:
15
additive manufacture of both the plurality of flow splitter segments and the plurality of
blades as a unit.
21. A centrifugal compressor impeller (60; 160) comprising:
a hub (62; 162) having a gaspath surface (64; 164) extending from a leading end to a trailing
end;
a plurality of blades (70A, 70B; 170) extending from the hub gaspath surface and each
having:
a leading edge (72A, 72B; 172);
25 a trailing edge (74A, 74B; 174);
a first face (80A, 80B; 180);
a second face (82A, 82B; 182); and
a tip (78A, 78B; 178); and
a circumferential ring (120, 122; 320, 322) extending between the blades and spaced from
30 both the hub gaspath surface and the tips of the blades.