MULTI ROW HYBRID DIFFUSER FOR A CENTRIFUGAL
COMPRESSOR
TECHNICAL FIELD
[0001] The present disclosure, in general, relates to improvement in efficiency
of radial compressors/blower using multiple rows of low solidity vanes.
BACKGROUND
[0002] Background description includes information that may be useful in
understanding the present invention. It is not an admission that any of the
information provided herein is prior art or relevant to the presently claimed
invention, or that any publication specifically or implicitly referenced is prior art.
[0003] In radial compressors, there is use of vaned diffuser and free vortex
diffuser. Free vortex diffusers are also called vaneless diffuser. Vaned diffuser
pressure recovery and efficiency is higher compared to vaneless diffuser.
Whereas, operating range of vanless diffuser is significantly wide compared to
vaned diffuser. Absence of throat makes vaneless diffuser to have wide range of
operation. In order to get more efficiency, vaned diffusers are shortened to avoid
throat are called low solidity vaned diffuser (LSD). Chord to pitch ratio of the
vane is defined as solidity. The LSD diffusers proved to give high pressure
recovery and efficiency without compromising much on operating range. But
again LSD has pressure recovery less than vaned diffuser.
[0004] Further improvement was realised with the tandem vanes, low solidity
design disclosed by, Seenoo et all. published in ASME 83-GT-3. The design is
like slited long airfoil in two halves. Later in 1989, Phiroze Bandukwalla et all,
got United States Patent 4824325 for “Diffuser having split tandem low Solidity
Vanes”. The vane split is alternative. Thereby, in second row the number of vanes
are half the number in first row. Most recent WIPO patent WO2016160393A1
“Diffuser having multiple rows of diffuser vanes with different solidity”, where,

first row of vane is with low solidity and rest of the rows are being used with high
solidity. Figure 3 of the patent clearly shows inducing throat in upstream vane row
by downstream row and vis-versa. This affects range of operation akin to vaned
diffuser.
[0005] In the present invention, multiple rows of solidity vaned diffuser are
achieved by hybridisation of vaneless diffuser and vaned diffuser calling it as
hybrid diffuser, where vaneless diffuser radial space is of the same order as radial
height of vanes, thereby, achieving multi row low solidity vaned diffuser with
throat less or large enough throat for wide range of operation. The invention
brings in different radial gap and solidity for subsonic and supersonic diffuser.
The important point to note is unless and otherwise mentioned, the description is
for subsonic impellers.
[0006] Figure 1 illustrates a prior art (ASME Paper 83-GT-3, 1983, Low-
solidity Tandem-cascade diffusers for wide flow range centrifugal compressor),
that shows two rows are as if the long vane slited into two. It appears there is no
radial gap between the two rows. The gap is seen due to circumferential relative
position at same radius. The second row vane is longer.
[0007] However, in the present invention the radial gap is order of vane radial
height. Also, second row is shorter and double in number compared to first row
whereas in the prior art it is reverse.
[0008] Figure 2 illustrates a prior art (US4824325, Diffuser having split
tandem low solidity vanes), that shows a second row 32 is placed in tandem with
first row 34 so as the wake flow 14 from trailing edge of first row 34 pass over
leading edge 15 of second row 32. Also the number of vanes in second row is
reduced to half.
[0009] However, in the present invention the number is doubled and chord
shortened. Also the second row airfoil is symmetrical airfoil whereas present
invention uses chambered airfoil to achieve more pressure recovery.

[0010] Figure 3 illustrates a prior art (WO2016160393A1, Diffuser having
multiple rows of diffuser vanes with different solidity), in which first row is with
pitch to chord ratio less than one and rest of two rows are with pitch to chord ratio
more than one. The figure clearly shows inducing of throat by second row of the
vane in first row and vis-versa due to high solidity second row and relatively
small radial gap of vaneless diffuser space compared with vane radial height.
Thereby, the pros and cons of the diffuser is akin to vaned diffuser.
[0011] However, in present invention the second row is with low solidity and
the radial gap is of same order as radial height of the vaned diffuser. In the present
invention the first row has pitch to chord ratio less than one for subsonic
centrifugal compressor while for supersonic centrifugal compressor the pitch to
chord ratio is order of 1.
[0012] Therefore, a multi row vaned diffuser with rationalised vaneless
diffuser space and solidity is required that can improve efficiency of radial
compressors/ blowers using multiple rows of low solidity vanes.
OBJECTS OF THE DISCLOSURE
[0013] Some of the objects of the present disclosure, which at least one
embodiment herein satisfy, are listed hereinbelow.
[0014] A general object of the present disclosure is to improve centrifugal
compressor efficiency by use of multiple rows of vanes with rationalised vaneless
diffuser space and solidity for subsonic and supersonic compressors.
[0015] An object of the present disclosure is to reduce second and third row
vane height in order to fit into shorter radial gap in order to accommodate multiple
rows of LSD.
[0016] Another object of the present disclosure is to remove induced throat
due to one row in adjacent row by rationalised radial space for vaneless diffuser
between the vane rows.

[0017] These and other objects and advantages of the present invention will
be apparent to those skilled in the art after a consideration of the following
detailed description taken in conjunction with the accompanying drawings in
which a preferred form of the present invention is illustrated.
SUMMARY
[0018] This summary is provided to introduce concepts related to a multi row
hybrid diffuser for a centrifugal compressor with rationalised vaneless diffuser
space and solidity for improving efficiency of radial compressors/ blowers using
multiple rows of low solidity vanes. The concepts are further described below in
the detailed description. This summary is not intended to identify key features or
essential features of the claimed subject matter, nor is it intended to be used to
limit the scope of the claimed subject matter.
[0019] In an embodiment, the present disclosure relates to a multi row hybrid
diffuser for a centrifugal compressor comprising a ring shaped diffuser transit
coupled with an impeller provisioned to rotate with a rotary shaft of the
centrifugal compressor wherein a plurality of first row vanes disposed radially
outwards from a first radial gap and extending into a second radial gap towards
the direction of rotation, a lead portion of the plurality of first row vanes nudges
the borderline of the first radial gap and a trail portion of the plurality of first row
vanes nudges the borderline of the second radial gap, wherein a first chord to
pitch ratio of the plurality of first row vanes is less than one, a plurality of second
row vanes disposed radially outwards from the second radial gap and extending
into a third radial gap, towards the direction of rotation, wherein a second chord to
pitch ratio of the plurality of second row vanes is less than one, a leading edge
portion of the plurality of second row vanes nudges the borderline of the second
radial gap and a trail portion of the plurality of second row vanes nudges the
borderline of the third radial gap; and a plurality of third row vanes disposed
radially outwards from the third radial gap towards the direction of rotation and
extending into a radius, towards the direction of rotation, wherein a third chord to

pitch ratio of the plurality of third row vanes is less than one, a lead portion of the
plurality of third row vanes nudges the borderline of the third radial gap and a trail
portion of the plurality of third row vanes nudges the radius, wherein combination
of the first radial gap, the second radial gap, and the third radial gap of first,
second and third vaneless diffusion portion along with the plurality of first row
vanes, the plurality of second row vanes and the plurality of third row vanes
constitute multi row hybrid diffuser for centrifugal compressor.
[0020] In an aspect, value of the first radial gap varies from 2mm to 0.2 times
radius R2.
[0021] In an aspect, the wide range value of the first radial gap is based on
flow angle, chord to pitch ratio, subsonic and supersonic and flow angle is
inversely proportional to value of the first radial gap.
[0022] In an aspect, value of the first vane radial height is calculated on the
basis of chord to pitch ratio that defines solidity.
[0023] In an aspect, the second radial gap is a free vortex vanless diffuser gap
and the value of the second radial gap is approximately equal to the value of the
first vane radial height.
[0024] In an aspect, value of the second vane radial height is calculated on the
basis of chord to pitch ratio that defines solidity and varies in the range of 0.6 to
0.75.
[0025] In an aspect, the third radial gap is a free vortex vaneless diffuser gap.
[0026] In an aspect, value of the third radial gap is approximately equal to the
value of the second vane radial height in case of subsonic compressors whereas
the value of the third radial gap is approximately equal to 1.67 times the value of
the second vane radial height and maximum solidity of adjacent plurality of row
vanes, in case of supersonic compressors.

[0027] In an aspect of the present embodiment, value of the third vane radial
height is calculated on the basis of chord to pitch ratio that defines solidity and
varies in the range of 0.6 to 2.
[0028] In an aspect of the present embodiment, the low solidity vane rows are
used for subsonic compressors whereas high solidity vane rows are used for first
and last row of supersonic compressors.
[0029] In an aspect of the present embodiment, the plurality of first row
vanes, the plurality of second row vanes, and the plurality of third row vanes
define an airfoil that is cambered and depicts an asymmetry between the two
acting surfaces of the airfoil.
[0030] In an aspect of the present embodiment, camber variation is in a way to
increase vane angle with reference to tangent of circle in direction of rotation on a
circle drawn from axis of rotation that makes vane radial as moved from leading
edge to trailing edge.
[0031] In an aspect of the present embodiment, the number of vanes increase
with radial position in the subsequent rows.
[0032] In an aspect of the present embodiment, increase in the number of
vanes may or may not be an integral multiple of number of vanes in the plurality
of first row vanes.
[0033] In an aspect of the present embodiment, the number plurality of row
vanes is directly proportional to the pressure ratio.
[0034] In an aspect of the present embodiment, the order of plurality of radial
gaps and the order of plurality of radial heights is approximately same with a
deviation of +/-20%, depending on the chord to pitch ratio.
[0035] In an aspect of the present embodiment, in case of variation in solidity,
the plurality of radial gaps is modified 1.67 times the maximum solidity of the
adjacent plurality of vane radial heights respectively.

[0036] In an aspect of the present embodiment, the plurality of low solidity
vanes may or may not be integral to hub or shroud of diffuser annular space after
impeller.
[0037] In an aspect of the present embodiment, the manufacturing of the
diffuser can be selected from casting, scoop milled or similar industrial
manufacturing process.
[0038] In an aspect of the present embodiment, first chord to pitch ratio of the
plurality of first row vanes, second chord to pitch ratio of the plurality of second
row vanes, and third chord to pitch ratio of the plurality of third row vanes defines
a low solidity diffuser.
[0039] Various objects, features, aspects, and advantages of the inventive
subject matter will become more apparent from the following detailed description
of preferred embodiments, along with the accompanying drawing figures in which
like numerals represent like components.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] The illustrated embodiments of the subject matter will be best
understood by reference to the drawings, wherein like parts are designated by like
numerals throughout. The following description is intended only by way of
example, and simply illustrates certain selected embodiments of devices, systems,
and methods that are consistent with the subject matter as claimed herein,
wherein:
[0041] Fig. 1 illustrates Low-solidity Tandem-cascade diffusers for wide flow
range centrifugal compressor as known in the art;
[0042] Fig. 2 illustrates Diffuser having split tandem low solidity vanes as
known in the art;
[0043] Fig. 3 illustrates diffuser having multiple rows of diffuser vanes with
different solidity, as known in the art;

[0044] Fig. 4 illustrates comprehensive view of a hybrid diffuser for
centrifugal compressor along with impeller, in accordance with an embodiment of
the present disclosure.
[0045] The figures depict embodiments of the present subject matter for the
purposes of illustration only. A person skilled in the art will easily recognize from
the following description that alternative embodiments of the structures and
methods illustrated herein may be employed without departing from the principles
of the disclosure described herein.
DETAILED DESCRIPTION
[0046] The detailed description of various exemplary embodiments of the
disclosure is described herein with reference to the accompanying drawings. It
should be noted that the embodiments are described herein in such details as to
clearly communicate the disclosure. However, the amount of details provided
herein is not intended to limit the anticipated variations of embodiments; on the
contrary, the intention is to cover all modifications, equivalents, and alternatives
falling within the scope of the present disclosure as defined by the appended
claims.
[0047] It is also to be understood that various arrangements may be devised
that, although not explicitly described or shown herein, embody the principles of
the present disclosure. Moreover, all statements herein reciting principles, aspects,
and embodiments of the present disclosure, as well as specific examples, are
intended to encompass equivalents thereof.
[0048] The terminology used herein is for the purpose of describing particular
embodiments only and is not intended to be limiting of example embodiments. As
used herein, the singular forms “a”, “an” and “the” are intended to include the
plural forms as well, unless the context clearly indicates otherwise. It will be
further understood that the terms “comprises”, “comprising”, “includes” and/or
“including,” when used herein, specify the presence of stated features, integers,
steps, operations, elements and/or components, but do not preclude the presence

or addition of one or more other features, integers, steps, operations, elements,
components and/or groups thereof.
[0049] In addition, the descriptions of "first", "second", “third”, and the like in
the present invention are used for the purpose of description only, and are not to
be construed as indicating or implying their relative importance or implicitly
indicating the number of technical features indicated. Thus, features defining
"first" and "second" may include at least one of the features, either explicitly or
implicitly.
[0050] It should also be noted that in some alternative implementations, the
functions/acts noted may occur out of the order noted in the figures. For example,
two figures shown in succession may, in fact, be executed concurrently or may
sometimes be executed in the reverse order, depending upon the functionality/acts
involved.
[0051] Unless otherwise defined, all terms (including technical and scientific
terms) used herein have the same meaning as commonly understood by one of
ordinary skill in the art to which example embodiments belong. It will be further
understood that terms, e.g., those defined in commonly used dictionaries, should
be interpreted as having a meaning that is consistent with their meaning in the
context of the relevant art and will not be interpreted in an idealized or overly
formal sense unless expressly so defined herein.
[0052] In the present subject matter, a multi row hybrid diffuser 2 for a
centrifugal compressor with rationalised vaneless diffuser space and solidity is
explained that improves efficiency of radial compressors/ blowers using multiple
rows of low solidity vanes. The multi row hybrid diffuser with rationalised
vaneless diffuser space and solidity of the present invention improves centrifugal
compressor efficiency by use of multiple rows of vanes with rationalised vaneless
diffuser space and solidity for subsonic and supersonic compressors. Further, the
present disclosure reduces second and third row vane height to fit into shorter
radial gap in order to accommodate multiple rows of LSD.

[0053] Figure. 1 illustrates a prior art (ASME Paper 83-GT-3, 1983, Low-
solidity Tandem-cascade diffusers for wide flow range centrifugal compressor),
that shows two rows are as if the long vane slited into two. It appears there is no
radial gap between the two rows. The gap is seen due to circumferential relative
position at same radius. The second row vane is longer. However, in the present
invention the radial gap is order of vane radial height. Also, second row is shorter
and double in number compared to first row whereas in the prior art it is reverse.
[0054] Figure 2 illustrates a prior art (US4824325, Diffuser having split
tandem low solidity vanes), that shows a second row 32 is placed in tandem with
first row 34 so as the wake flow 14 from trailing edge of first row 34 pass over
leading edge 15 of second row 32. Also the number of vanes in second row is
reduced to half. However, in the present invention the number is doubled and
chord shortened. Also the second row airfoil is symmetrical airfoil whereas
present invention uses chambered airfoil to achieve more pressure recovery.
[0055] Figure 3 illustrates a prior art (WO2016160393A1, Diffuser having
multiple rows of diffuser vanes with different solidity), in which first row is with
pitch to chord ratio less than one and rest of two rows are with pitch to chord ratio
more than one. The figure clearly shows inducing of throat by second row of the
vane in first row and vis-versa due to high solidity second row and relatively
small radial gap of vaneless diffuser space compared with vane radial height.
Thereby, the pros and cons of the diffuser is akin to vaned diffuser. However, in
present invention the second row is with low solidity and the radial gap is of same
order as radial gap of the vaned diffuser. In the present invention the first row has
pitch to chord ratio less than one for subsonic centrifugal compressor while for
supersonic centrifugal compressor the pitch to chord ratio is order of 1.
[0056] Referring to Fig. 4, the hybrid diffuser 2 for centrifugal compressor
along with impeller 1 is shown. There are three rows of low solidity vane, first
row or inner row 3 and second row or mid row 4, third row or outer row 5. All the
rows are with low solidity, meaning pitch to chard ratio less than 1. All the vanes

are chambered 12, 13, 14 in a way to make vane radial as moved from leading
edge 6,7,8 to trailing edge 9, 10, 11. NACA65 profile is used in all the set of
rows. The gap between vane rows is vaneless diffusion region.
[0057] AR1 is radial gap 22 between circle of radius 16 R3 at leading edge
and impeller 2 outer radius 15 R2. AR1 has wide range based on flow angle,
pinch, subsonic and supersonic. Higher the flow angle lower is the AR1. AR1
varies from 2 mm to 0.2 times R2. Minimum gap and high solidity close to 1 can
be used for supersonic impellers.
[0058] AR2 23 is radial height of first row vane 3. The value of AR2 is
calculated from solidity.
[0059] AR3 is radial gap 24 between circle of radius 18 R5 at leading edge 7
and radius 17 R4 at trailing edge 9. This is a free vortex vanless diffuser space.
AR3 « AR2.
[0060] AR4 25 is radial height of second row vane 4. The value of AR4 is
calculated from solidity. The solidity varies from 0.6 to 0.75
[0061] AR5 is radial gap 26 between radius 20 R7 at third row leading edge 8
and radius 19 R6 at trailing edge 10 of second vane row. This is a free vortex
vanless diffuser space. For subsonic compressor, AR5^AR4. And for supersonic
compressors, AR5 « 1.67*AR4*maximum solidity of adjacent vane row. The
rationalisation of vaneless diffuser space and solidity is used for subsonic
compressor with ±20% deviation for varied solidity.
[0062] AR6 27 is radial height of third row vane 5. The value of AR6 is
calculated from solidity. The solidity varies from 0.6 to 2. Low solidity vane rows
are used for subsonic compressors while higher solidity vane rows are used for
supersonic compressors.
[0063] ∆R2n+1 (not shown in figure) where ‘n’ is total number of rows of
vanes in the hybrid diffuser is a radial space after nth row depends on available

radial space and downstream component and can be incorporated accordingly
depending upon the requirement/constraints.
[0064] In an aspect, value of the first radial gap ∆R1 varies from 2mm to 0.2
times radius R2.
[0065] In an aspect, the wide range value of the first radial gap ∆R1 is based
on flow angle, chord to pitch ratio, subsonic and supersonic and flow angle is
inversely proportional to value of the first radial gap ∆R1.
[0066] In an aspect, value of the first radial height ∆R2 is calculated on the
basis of chord to pitch ratio that defines solidity.
[0067] In an aspect, the second radial gap ∆R3 is a free vortex vanless diffuser
gap and the value of the second radial gap ∆R3 is approximately equal to the
value of the first radial height ∆R2.
[0068] In an aspect, value of the second radial height ∆R4 is calculated on the
basis of chord to pitch ratio that defines solidity and varies in the range of 0.6 to
0.75.
[0069] In an aspect, the third radial gap ∆R3 is a free vortex vanless diffuser
gap.
[0070] In an aspect, value of the third radial gap ∆R5 is approximately equal
to the value of the second radial height ∆R4 in case of subsonic compressors
whereas the value of the third radial gap ∆R5 is approximately equal to 1.67 times
the value of the second radial height ∆R4 and maximum solidity of adjacent
plurality of row vanes, in case of supersonic compressors.
[0071] In an aspect, value of the third radial height ∆R6 is calculated on the
basis of chord to pitch ratio that defines solidity and varies in the range of 0.6 to 2.
[0072] In an aspect, the low solidity vane rows are used for subsonic
compressors whereas high solidity vane rows are used for supersonic
compressors.

[0073] In an aspect, the plurality of first row vanes 3, the plurality of second
row vanes 4, and the plurality of third row vanes 5 define an airfoil that that is
cambered and depicts an asymmetry between the two acting surfaces of the
airfoil.
[0074] In an aspect, camber variation is in a way to increase vane angle with
reference to tangent of circle in direction of rotation on a circle drawn from axis
of rotation that makes vane radial as moved from leading edge to trailing edge.
[0075] In an aspect, the number of vanes increase with radial position in the
subsequent rows.
[0076] In an aspect, increase in the number of vanes may or may not be an
integral multiple of number of vanes in the plurality of first row vanes 3.
[0077] In an aspect, the number plurality of row vanes 3, 4, 5 is directly
proportional to the pressure ratio.
[0078] In an aspect, the order of plurality of radial gaps ∆R1, ∆R3, and ∆R5
and the order of plurality of radial heights ∆R2, ∆R4, and ∆R6 is approximately
same with a deviation of +/-20%, depending on the chord to pitch ratio.
[0079] In an aspect, in case of variation in solidity, the plurality of radial gaps
∆R1, ∆R3, and ∆R5 is modified 1.67 times the maximum solidity of the adjacent
plurality of radial heights ∆R2, ∆R4, and ∆R6 respectively.
[0080] In an aspect, the plurality of low solidity vanes 3, 4, 5 may or may not
be integral to hub or shroud of diffuser annular space after impeller.
[0081] In an aspect, the manufacturing of the diffuser can be selected from
casting, scoop milled or similar industrial manufacturing process.
[0082] In an aspect, the first chord to pitch ratio of the plurality of first row
vanes 3, second chord to pitch ratio of the plurality of second row vanes 4, and
third chord to pitch ratio of the plurality of third row vanes 5 defines a low
solidity diffuser

[0083] The invention enables reduction of velocity in diffuser to larger extent
that the losses at throat of volute, and scroll gets reduced. The invention
particularly suitable for last stage of multistage compressor and single stage
compressor where the flow is discharging into collector, scroll, tongue less
discharge volute. In a CFD simulation, for a typical compressor, the efficiency
improvement with one row is 7% while with two rows the efficiency
improvement is ~11% rise. Thus the present invention helps to rise additional
efficiency by 4-6% without considerable compromise on operating range.
[0084] Further, the terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of the disclosure. It
will be appreciated that several of the above-disclosed and other features and
functions, or alternatives thereof, may be combined into other systems or
applications. Various presently unforeseen or unanticipated alternatives,
modifications, variations, or improvements therein ma y subsequently be made by
those skilled in the art without departing from the scope of the present disclosure
as encompassed by the following claims.
[0085] It will be appreciated that variants of the above-disclosed and other
features and functions, or alternatives thereof, may be combined into many other
different systems or applications. Various presently unforeseen or unanticipated
alternatives, modifications, variations, or improvements therein may be
subsequently made by those skilled in the art which are also intended to be
encompassed by the following claims.
[0086] While the foregoing describes various embodiments of the invention,
other and further embodiments of the invention may be devised without departing
from the basic scope thereof. The scope of the invention is determined by the
claims that follow. The invention is not limited to the described embodiments,
versions or examples, which are included to enable a person having ordinary skill
in the art to make and use the invention when combined with information and
knowledge available to the person having ordinary skill in the art.

We claim:
1. A multi row hybrid diffuser (2) for a centrifugal compressor comprising:
a ring shaped diffuser transit coupled with an impeller provisioned
to rotate with a rotary shaft of the centrifugal compressor;
characterized in that:
a plurality of first row vanes (3) disposed radially outwards from a
first radial gap (∆R1) and extending into a second radial gap (∆R3)
towards the direction of rotation,
a lead portion (6) of the plurality of first row vanes (3) nudges the
borderline of the first radial gap (∆R1) and a trail portion (9) of the
plurality of first row vanes (3) nudges the borderline of the second radial
gap (∆R3), wherein a first chord to pitch ratio of the plurality of first row
vanes (3) is less than one;
a plurality of second row vanes (4) disposed radially outwards from
the second radial gap (∆R3) and extending into a third radial gap (∆R5),
towards the direction of rotation, wherein a second chord to pitch ratio of
the plurality of second row vanes (4) is less than one,
a leading edge portion (7) of the plurality of second row vanes (4)
nudges the borderline of the second radial gap (∆R3) and a trail portion
(10) of the plurality of second row vanes (4) nudges the borderline of the
third radial gap (∆R5); and
a plurality of third row vanes (5) disposed radially outwards from the
third radial gap (∆R5) towards the direction of rotation and extending into
a radius (21), towards the direction of rotation, wherein a third chord to
pitch ratio of the plurality of third row vanes (5) is less than one,

a lead portion (8) of the plurality of third row vanes (5) nudges the
borderline of the third radial gap (∆R5) and a trail portion (11) of the
plurality of third row vanes (5) nudges the radius (21),
wherein combination of the first radial gap (∆R1), the second radial
gap (∆R3), and the third radial gap (∆R5) of first, second and third
vaneless diffusion portion along with the plurality of first row vanes (3),
the plurality of second row vanes (4) and the plurality of third row vanes
(5) constitute multi row hybrid diffuser for centrifugal compressor.
2. The multi row hybrid diffuser (2) as claimed in claim 1, wherein value of
the first radial height (∆R2), second radial height (∆R4), the third radial
height (∆R6) generalized as ∆R2n, where n is nth van row, is calculated on
the basis of chord to pitch ratio that defines solidity.
3. The multi row hybrid diffuser (2) as claimed in claim 1, wherein value of
solidity differs for subsonic and supersonic compressors where the value
of solidity is in the range of 0.6 to 0.75 for subsonic compressors while for
supersonic compressor the solidity for first row is order of one and last
row vane solidity vary from 0.6 to 2 whereas intermediate rows solidity
value is in the range of 0.6 to 0.75.
4. The multi row hybrid diffuser (2) as claimed in claim 1, wherein value of
the first radial gap (∆R1) varies from 2mm to 0.2 times radius (R2).
5. The multi row hybrid diffuser (2) as claimed in claim 1, wherein the radial
gaps at any row, ∆R2n-1 is rationalized in terms of solidity as 1.67 times
maximum solidity of adjacent vane rows times maximum radial height of
adjacent vane row with +/-20% deviation in a way to occupy equal order
radial space compared to vane radial heights ∆R2n for vaneless free vortex
diffusion that turns to ∆R2n-1 « ∆R2n for subsonic compressors and
∆R2n-1 >= ∆R2n for n value 1, n and ∆R2n-1 « ∆R2n for n value 2 to n-1
for supersonic compressor whereas radial gap after last row, ∆R2n+1,

depends on available radial space due to downstream component and
geometric constraints.
6. The multi row hybrid diffuser (2) as claimed in claim 1, wherein the
plurality of first row vanes (3), the plurality of second row vanes (4), and
the plurality of third row vanes (5) define an airfoil that that is cambered
and depicts an asymmetry between the two acting surfaces of the airfoil
where the camber variation is in a way to increase vane angle with
reference to tangent of circle in direction of rotation on a circle drawn
from axis of rotation that makes vane radial as moved from leading edge
to trailing edge.
7. The multi row hybrid diffuser (2) as claimed in claim 1, wherein the
number of vanes in a row increase with radial position in the subsequent
rows and the number of vanes in a row may or may not be an integral
multiple of number of vanes in the plurality of number of vanes in first
row vanes (3).
8. The multi row hybrid diffuser (2) as claimed in claim 17, wherein the
plurality of low solidity vanes (3, 4, 5) may or may not be as a single piece
as part of a hub or shroud in diffuser annular space after impeller.
9. The multi row hybrid diffuser (2) as claimed in claim 1, wherein the
manufacturing of the diffuser can be selected from casting, scoop milled or
similar industrial manufacturing process.
10. The multi row hybrid diffuser (2) as claimed in claim 1, wherein leading
edge radius is of order 0.12 to 0.45 times maximum vane thickness