SHROUDED 3D IMPELLER FOR CENTRIFUGAL COMPRESSOR
STAGES WITH HIGH FLOW COEFFICIENT
FIELD OF INVENTION:
[001] The present subject matter described herein, relates to a 3D impeller of
centrifugal compressor stages with high flow coefficient and, in particular, to
impeller geometrical parameters along meridional flow path from impeller inlet to
impeller exit. The present subject matter is more particularly relates to shrouded
3D impeller with high flow coefficient ranging from 0.134 to 0.127 of centrifugal
compressor stage.
BACKGROUND AND PRIOR ART AND PROBLEM IN PRIOR ART:
[002] In general, 3D impeller of centrifugal compressors comprises two rotary
discs, i.e., a disk and a shroud, and a plurality of vanes. Further, the 3D impeller
of centrifugal compressors has a hub disc where the impeller vanes are connected
and a shroud disc which is welded to the hub disc through the impeller blades to
form flow passage by means of the disc and the shroud and the vanes. The
plurality of vanes is disposed between the hub disc and the shroud and
substantially equidistantly in a circumferential direction to define the flow passage
by means of the disk and the shroud and the vanes. Apart from the manufacturing
quality like surface finish of the impeller, the impeller blade geometry plays a
significant role in the aerodynamic efficiency. The geometric parameters of the
blade of the impeller determine the distribution of the relative velocities of the
fluid flow along the rotor, diffusion of fluid within the impeller, blade to blade
loading at hub, shroud and intermediate planes, and flow passage area distribution
that affect the flow behavior in the flow path and various internal and the external
losses.
[003] US patent no. US 6,082,890 dated 04/07/2000 titled “High axial flow glass
coated impeller” describes a glass coated high axial flow impeller, including a hub
and attached blades. The hub has a centrally located hole, where the hole has a
central axis. The impeller has a plurality of angles and edges, all of which have a

rounded configuration to permit glassing. The impeller further includes at least
two variable pitch blades. Each blade has front and rear surfaces both defined by
an inside edge having a leading end and a trailing end, an outside edge having a
leading end and a trailing end, a leading edge connecting the leading end of the
inside edge to the leading end of the outside edge and a trailing edge that connects
the trailing end of the inside edge to the trailing end of the outside edge. Fig. 1
illustrates the design of the impeller of the present US patent. High axial flow
impellers, comprising a hub and attached blades with glass coated in dual hub
format for mixing purpose which is similar to propellers as commonly found on
boats is described in the present US patent. Further, US patent 890’ is related to
glass coated configurations of high flow axial impellers those could not be
manufactured because such high axial flow metal impellers have many angles and
edges that are generally believed to prevent effective glass coating.
[004] US patent no. US 6715991B2, dated 06/04/2004 titled “Rotor blade for
centrifugal compressor with a medium flow coefficient” describes a cylindrical
blade for a rotor of the purely radial type of impeller that is 2D in nature and
typical coordinates with varying radius. Fig. 2 illustrates the design of impeller of
the present US patent 991. The suction and pressure surface of the vane referred a
convex and concave surface respectively. The coordinates are fixed and are given
as ratio of the impeller exit radius. In the present US patent 991, geometry of the
impeller is in Cartesian co-ordinates in terms of impeller exit radius which is 200
mm.
[005] US patent no. US 7563074 B2, dated 21/07/2009 titled “Impeller for a
centrifugal compressor” describes impeller rotatable in a direction of rotation in a
centrifugal compressor having an intake ring. Fig. 3 illustrates the impeller of
present US patent 074. In the present US patent 074, the impeller is an open
impeller without shroud disc generally of single stage of very high operating tip
speed suitable for turbo chargers. The impeller includes a back plate having a hub
portion and a plurality of blades that extend from the back plate. Each blade
includes a leading edge that extends radially outward along a non-linear path from

adjacent the hub portion. Further it relates to centrifugal compressor impeller of
open type without shroud surface for very high speed applications like turbo
charging.
[006] US patent no. US 8,308,420 B2 dated 13/11/2012, titled “Centrifugal
compressor, impeller and operating method of the same” describes a centrifugal
compressor is equipped with an impeller having a blade angle distribution that
makes it possible to achieve a relatively wide operating range. The blade angle of
a shroud side facing a circular plate of a blade is termed a first angle and a blade
angle of a hub side disposed at the circular plate is a second. The shroud side is
formed in a curved shape having an angle distribution from a front area in a shaft
direction toward a centrifugal direction in which the first angle is the local
maximum point before a substantially middle portion and the local minimum
point after the substantially middle point. Fig. 4 illustrates the blade angle
distribution of the impeller at the inlet and exit of the blade.
[007] One of the main demands from all the present industries is the high
aerodynamic efficiency that needs to be achieved in all the stages of multi stage
compressor where the 3D impellers are employed. None of the above mentioned
prior arts discusses about the efficiency improvement of 3D impeller and current
efficiency levels achieved are not mentioned. It is required to improve the
efficiency of 3D impeller of multi-stage centrifugal compressor which is very
close to the theoretical efficiency by adopting proper impeller geometry.
Therefore, it is required to improve the efficiency of 3D impeller of centrifugal
compressor stage that is primarily used for handling high volume flows, such as
natural gas application. Accordingly, it is necessary to provide proper impeller
geometry which provides high aerodynamic efficiency of working at all stages of
the multi-stage compressor.
OBJECTS OF THE INVENTION:
[008] The principal objective of the present invention is to provide a geometrical
parameter, i.e., blade angle distribution of 3D impeller with high flow coefficient

along the meridional flow path from impeller inlet to impeller exit to achieve high
aerodynamic efficiency in the centrifugal compressor stage.
[009] Another object of the present invention is to provide geometrical
parameter, i.e., blade wrap angle of 3D impeller with high flow coefficient along
the meridional flow path from the impeller inlet to the impeller exit to achieve
high aerodynamic efficiency in the centrifugal compressor stage.
[0010] Another object of the present invention is to provide geometrical
parameter, i.e., blade curvature at hub and shroud of 3D impeller with the high
flow coefficient along the meridional flow path from the impeller inlet to impeller
exit to achieve high aerodynamic efficiency in the centrifugal compressor stage.
[0011] Another object of the present invention is to provide geometrical
parameter, i.e., contours slopes at hub and shroud of 3D impeller with the high
flow coefficient along the meridional flow path from the impeller inlet to impeller
exit to achieve high aerodynamic efficiency in the centrifugal compressor stage.
[0012] Another object of the present invention is to provide geometrical
parameter, i.e., passage area distribution in 3D impeller with high flow coefficient
along the meridional flow path from the impeller inlet to impeller exit to achieve
high aerodynamic efficiency in the centrifugal compressor stage.
[0013] Another object of the present invention is to provide geometrical
parameter, i.e., circumferential pitch of the blade in 3D impeller with high flow
coefficient.
[0014] Another object of the present invention is to provide geometrical
parameter, i.e., an inlet hub radius of 3D impeller with high flow coefficient along
the meridional flow path from the impeller inlet to impeller exit to achieve high
aerodynamic efficiency in the centrifugal compressor stage.
[0015] Another object of the present invention is to provide geometrical
parameter, i.e., an inlet shroud radius of 3D impeller with high flow coefficient
along the meridional flow path from the impeller inlet to impeller exit to achieve
high aerodynamic efficiency in the centrifugal compressor stage.

[0016] Yet another object of the present invention is to provide geometrical
parameter, i.e., blade lean angle of 3D impeller with high flow coefficient along
the meridional flow path from the impeller inlet to impeller exit to achieve high
aerodynamic efficiency in the centrifugal compressor stage.
[0017] Yet another object of the present invention is to provide geometrical
parameter, i.e., blade width at exit of 3D impeller with high flow coefficient along
the meridional flow path from the impeller inlet to impeller exit to achieve high
aerodynamic efficiency in the centrifugal compressor stage.
SUMMARY OF THE INVENTION:
[0018] The present subject matter relates to 3D impeller of centrifugal compressor
stage for compressing fluid with high aerodynamic efficiency. The 3D impeller
comprises a rotor, a hub disc (1) and shroud disc (3). Further, the 3D impeller
comprises a plurality of blades radially protruding from the hub disc (1) and
spaced equidistantly on circumference of the hub disc (1). In the present 3D
impeller, blade angle distribution at inlet and exit of impeller at the hub disc (1) is
(-) 51o deg. and (-) 40o deg. respectively with maximum angle (-) 10o deg. at 50%
of meridional flow path length. Further, the present 3D impeller adopts
appropriate Blade angle distribution, Wrap angle distribution, Passage area
distribution, Slope & Curvatures at hub and shroud sections from inlet to exit of
impeller to achieve high aerodynamic efficiency.
[0019] In order to further understand the characteristics and technical contents of
the present subject matter, a description relating thereto will be made with
reference to the accompanying drawings. However, the drawings are illustrative
only but not used to limit scope of the present subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] It is to be noted, however, that the appended drawings illustrate only
typical embodiments of the present subject matter and are therefore not to be
considered for limiting of its scope, for the invention may admit to other equally
effective embodiments. The detailed description is described with reference to the

accompanying figures. In the figures, a reference number identifies the figure in
which the reference number first appears. The same numbers are used throughout
the figures to reference like features and components. Some embodiments of
system or methods or structure in accordance with embodiments of the present
subject matter are now described, by way of example, and with reference to the
accompanying figures, in which:
[0021] Fig.1, Fig. 2, Fig. 3, and Fig. 4 illustrate the view of the impeller of
centrifugal compressor known in the art;
[0022] Fig. 5 illustrates a 3D view of impeller having twisted 3D impeller blade,
in accordance with an embodiment of the present subject matter;
[0023] Fig. 6 illustrates cross sectional view of the impeller with hub and shroud
disc, in accordance with an embodiment of the present subject matter;
[0024] Fig. 7 illustrates impeller blade angle distribution from inlet to exit at hub
and shroud surfaces of the impeller, in accordance with an embodiment of the
present subject matter;
[0025] Fig. 8 illustrates impeller blade wrap angle distribution from inlet to exit at
hub and shroud surfaces of the impeller, in accordance with an embodiment of the
present subject matter;
[0026] Fig. 9 illustrates impeller blade slop distribution from inlet to exit at hub
and shroud surfaces of the impeller, in accordance with an embodiment of the
present subject matter;
[0027] Fig. 10 illustrates impeller blade curvature distribution from inlet to exit at
hub and shroud surfaces of the impeller, in accordance with an embodiment of the
present subject matter;
[0028] Fig. 11 illustrates impeller blade lean angle distribution from inlet to exit
of the impeller along impeller meridional flow path length, in accordance with an
embodiment of the present subject matter;

[0029] Fig. 12 illustrates impeller blade to blade loading distribution of the
impeller, in accordance with an embodiment of the present subject matter;
[0030] Fig. 13 illustrates relative velocity distribution on the impeller blade at
both suction and pressure surfaces at hub and shroud sections of the impeller, in
accordance with an embodiment of the present subject matter;
[0031] Fig. 14 (a) and (b) illustrate pressure recovery coefficient and mean
pressure recovery coefficient at pressure side and suction side at hub and shroud
sections of the impeller, in accordance with an embodiment of the present subject
matter;
[0032] Fig. 15 (a) and (b) illustrate static pressure distribution on the blade
suction and pressure surfaces at hub and shroud sections of the impeller
respectively, in accordance with an embodiment of the present subject matter; and
[0033] Fig. 16 illustrate gradual increase in impeller passage area along the
meridional flow path length of impeller from inlet to exit,in accordance with an
embodiment of the present subject matter.
[0034] 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.
DESCRIPTION OF THE PREFERRED EMBODIMENTS:
[0035] The subject matter disclosed herein relates to 3D impeller of centrifugal
compressor stage with high flow coefficient ranging from 01.34 to 0.127 of the
centrifugal compressor stage. In the centrifugal compressor fluid is compressed to
a desired pressure and enters axially at the first stage and gets compressed in the
impeller and passes through a diffuser, “U” shaped bend and through a row of
plurality of vanes or blades in the return channel that reduces the tangential or
swirl component of flow, and then enters the next stage impeller for further
compression. Every multi stage compressors has high flow coefficient stages in

the beginning followed by medium and low flow coefficient stages as the gas gets
compressed in every stage and the volume that has to be handled by the
subsequent stages is reduced continuously. The pressurized gas from the last stage
impeller goes into a volute/collector chamber that concentrically arranged inside
the inter-stage duct.
[0036] In the present subject matter, 3D impeller geometrical parameters, such as
Blade angle, Wrap angle, Slope, Curvature, Passage area, Inlet hub radius, Inlet
shroud radius, Impeller blade exit width, Impeller blade circumferential pitch are
achieved along the meridional flow path for high aerodynamic efficiency. The 3D
impellers are made according to achieved geometrical parameters which give high
aerodynamic efficiency which is very close to theoretical efficiency. The present
geometrical parameters make the 3D impeller more efficient and increase the
overall efficiency of the centrifugal compressor at every stage.
[0037] All impellers of the centrifugal compressors have the same dimensions,
they only differ in the channel length and the geometry. With the change in
geometry, noticeable differences in the aerodynamic efficiency can be seen. The
blade angles are different on the impeller at the inlet and at the exit edge. Thus
there has to be a transition in the blade angle along the meridional flow path
length of the blade. The blade angle distribution has a significant effect on
impeller efficiency. Therefore, the geometry of the blade is often mechanically
complicated and the accuracy of the flow prediction varies with the geometry of
the meridional flow path. Further, the blade angle distribution at hub along the
meridional flow path has greater effect on the aerodynamic efficiency as
compared to blade angle distribution at the shroud.
[0038] Further, centrifugal compressors with 3D impeller are basically meant for
yielding higher aerodynamic efficiency. All the elements of compressor stage like
Inducer, Impeller, Diffuser, U bend, Return channel and Exit element contributes
to the higher efficiency. However, impeller of the compressors where in the
energy is added to the working fluid plays main role in achieving higher
efficiency. To achieve higher efficiency, compressor demands proper blade

loading, Relative velocity distribution and Static pressure distribution of the
impeller blade that results in fluid flow without flow recirculation, flow
separation, low momentum zone in the entire flow path of compressor stage. This
can be achieved by adopting appropriate Blade angle distribution, Wrap angle
distribution, Passage area distribution, Slope & Curvatures at hub and shroud
sections from inlet to exit of impeller.
[0039] As explained above in the problem in prior art section, the efficiency of
the impeller is low, and there are more frictional losses and less blade loading.
Design and structure of the impeller is not capable to achieve the high efficiency.
Geometrical parameters of the impeller, known in the art, provide less efficiency
and more frictional losses.
[0040] According to an implementation of the present subject matter, an impeller
blade angle “β” distribution at impeller hub and shroud surfaces along the
impeller inlet to impeller exit along the meridional flow path is defined. The blade
angle distribution completely controls the flow physics within the impeller like
diffusion, pressure recovery coefficient, pressure loss coefficient, relative velocity
distribution, impeller passage area distribution, flow pattern at impeller exit and
along the downstream of the compressor stage. The blade angle distribution from
the inlet to outlet of an impeller in a centrifugal compressor at each stage provides
significant influence on its flow characteristics. Further, the blade angle
distribution explains performance, loss generation, and operating range of the
impeller in the centrifugal compressor.
[0041] It should be noted that the description and figures merely illustrate the
principles of the present subject matter. It should be appreciated by those skilled
in the art that conception and specific embodiment disclosed may be readily
utilized as a basis for modifying or designing other structures for carrying out the
same purposes of the present subject matter. It should also be appreciated by those
skilled in the art that by devising various arrangements that, although not
explicitly described or shown herein, embody the principles of the present subject
matter and are included within its spirit and scope. Furthermore, all examples

recited herein are principally intended expressly to be for pedagogical purposes to
aid the reader in understanding the principles of the present subject matter and the
concepts contributed by the inventor(s) to furthering the art, and are to be
construed as being without limitation to such specifically recited examples and
conditions. The novel features which are believed to be characteristic of the
present subject matter, both as to its organization and method of operation,
together with further objects and advantages will be better understood from the
following description when considered in connection with the accompanying
figures.
[0042] These and other advantages of the present subject matter would be
described in greater detail with reference to the following figures. It should be
noted that the description merely illustrates the principles of the present subject
matter. It will thus be appreciated that those skilled in the art will be able to devise
various arrangements that, although not explicitly described herein, embody the
principles of the present subject matter and are included within its scope.
[0043] Fig. 5 illustrates top view of 3D impeller, in accordance with the present
subject matter. In the fig. 5, it shows the location of the exit and inlet vanes of the
3D impeller. Fig. 6 illustrates the cross section of the 3D impeller, in accordance
with the present subject matter. The 3D impeller has rotor shaft and a hub disc 1
and shroud disc 2 connected to the rotor. Further, the hub disc has two parts hub
disc 1 and hub contour 2. Similarly, the shroud disc has two parts shroud disc 3
and shroud disc 4. Further, the 3D impeller has a plurality of blades/vanes 5 (in
fig. 6 cross section of one blade of the impeller is shown for clarity) supported by
the hub disc 1 and radially protruding from the disc. The plurality of blades 6 is
circumferentially and equidistantly spaced on the disc. Further, the plurality of
blades, interchangeably can be referred as blade, 5 are covered by the shroud disc
and contour 3, 4 which forms an outer surface or boundary to flow of liquid in a
flow passage defining a flow direction. The plurality of blades 5 is disposed
between the hub disc and the shroud disc and substantially equidistantly in a
circumferential direction to define the flow passage by means of the disc and the

shroud and the vanes. The width of the Impeller blade ‟B2” plays major role in
achieving the overall efficiency of compression stage. Impeller inlet hub radius
“R1h” in centrifugal compressor stage affects the roto-dynamic behaviour of the
compressor. In the centrifugal compressor, higher inlet hub radius “R1h” demands
higher inlet shroud radius “R1s” which increases the inlet relative velocity at
shroud.
[0044] Fig. 7 illustrates impeller blade angle distribution from inlet to exit at hub
and shroud surfaces of the 3D impeller with high flow coefficient, in accordance
with an embodiment of the present subject matter. The impeller blade angle
distribution plays an important role in the functioning and efficiency of the
centrifugal compressor. The blade angle distribution completely controls the flow
physics within the impeller, such as diffusion, pressure recovery coefficient,
pressure loss coefficient, relative velocity distribution, impeller passage area
distribution, flow pattern at impeller exit and along the downstream of the
compressor stage. The impeller blade angle distribution at hub and shroud
sections along the percentage length of meridional flow path “A” is governed by
Equation.1 and Equation.2 respectively.
For Hub

[0045] Further, the blade angle distribution of the 3D impeller with high flow
coefficient at inlet is (-) 51o deg. and at exit is (-) 40o deg. of impeller at hub disc
(1). Location of the maximum angle of the blade angle distribution at hub disc (1)
is at 50% of meridional flow path length. Further, the maximum angle is (-) 10o
deg at the meridional flow path length. Furthermore, the impeller blade angle
distribution for shroud disc at inlet is (-) 55 deg. and at exit is (-) 45 deg. Location

of the maximum angle of the blade angle distribution at the shroud disc (3) is at
75% of meridional flow path length. Further, the maximum angle at the shroud
disc is (-) 37o deg.
[0046] Fig. 8 illustrates impeller blade wrap angle distribution from inlet to exit at
hub and shroud surfaces of the 3D impeller with high flow coefficient, in
accordance with an embodiment of the present subject matter. The Impeller wrap
angle “θ” distribution at impeller hub and shroud surfaces from impeller inlet to
impeller exit influences blade loading / relative velocity distribution, the pressure
recovery, flow behaviour and thereby efficiency of the centrifugal compressor.
The present subject matter explains the wrap angle distribution which decreases
uniformly from impeller inlet to impeller exit for achieving higher efficiency as
shown in Fig. 8. For the high flow coefficient 3D impellers, the wrap angle
variation is in range of 0.00 deg. to (-) 400 deg. for shroud; and (-) 50 to (-) 45o
deg. for the hub with respect to the meridional plane or meridional flow path as
shown in fig. 8. The impeller wrap angle variation at the hub and the shroud
sections along the percentage length of meridional flow path “A” is governed by
Equation.3 and Equation.4 respectively.
For Hub

[0047] Fig. 9 illustrates impeller blade slop distribution from inlet to exit at hub
and shroud surfaces of the impeller, in accordance with an embodiment of the
present subject matter. The impeller hub and shroud disc contours slopes
influence the blade loading, relative velocity distribution, pressure rise and there
by overall efficiency of the 3D impeller with high flow coefficient. Variation in
slope with respect to meridional plane at hub & shroud surface is shown in Fig.9.
The present subject matter explains the slope of 0.0o deg. at inlet and 75o deg. at

exit at the shroud surface, whereas the slope is 14o deg. and 90o deg. at hub
surface of the impeller. The variation of the slope “S” of the impeller at hub and
shroud sections along the percentage length of meridional flow path “A” is
governed by Equation.5 and Equation.6 respectively.
At Hub

[0048] Fig. 10 illustrates impeller blade curvature distribution from inlet to exit at
hub and shroud surfaces of the 3D impeller with high flow coefficient, in
accordance with an embodiment of the present subject matter. The curvatures of
impeller blade at hub and shroud contours influences the blade loading, relative
velocity distribution, pressure rise and there by overall efficiency of the 3D
impeller with high flow coefficient. Variation in curvature results in higher
efficiency in the present subject matter at hub and shroud surfaces as shown in
Fig.10. Hub curvature at impeller inlet and exit is 0.0025 & 0.0065 respectivel,
and the maximum curvature is 0.008(1/mm) located between the 60% to 80% of
meridional length. Similarly, shroud Hub curvature at impeller inlet & exit is
0.0005 & 0.0085 respectively, and the maximum curvature is 0.013 (1/mm)
located between 55% and 75% of meridional flow path length. The impeller
curvatures “C” variation at hub and shroud sections along the percentage length of
meridional flow path “A” is governed by Equation.7 and Equation.8 respectively.
At Hub

At Shroud


[0049] Other embodiment of the present subject matter explains circumferential
pitch of the impeller blades in terms of degree which depends on the total number
of blade in the impeller. The number of blades shows major impact on the peak
blade loading and total frictional losses. It is observed that low flow stages
requires lesser number of impeller blades whereas high flow stages demands more
number of impeller blades to achieve proper blade loading which results in
efficient flow behavior in the entire compressor stage. For the present subject
matter which is a high flow impeller, the circumferential pitch is in range of 24o
deg. to 21o deg. for achieving better blade loading and lesser friction losses which
has ultimately resulted higher efficiency.
[0050] Another embodiment of the present subject matter relates to impeller inlet
hub radius ‟R1h” in a centrifugal compressor stage. Where higher inlet hub radius
“R1h”demands higher inlet shroud radius which increases the inlet relative
velocity at the shroud. The Inlet tip velocity reduces the impeller diffusion rate
and accordingly pressure recovery and impeller efficiency. Inlet hub radius
“R1h”also influences every stage of the centrifugal compressor shaft diameter in
view of compressor rotodynamic behaviour. Therefore, considering above all
requirements, for the present subject matter which has 450 mm impeller diameter
with flow range of 70% to 130% of design flow. Further, the inlet hub diameter is
37% to 39% of impeller exit hub diameter.
[0051] In another embodiment, the Impeller inlet shroud radius "R1s” (as shown
in fig. 6) is free to increase or decrease whereas the hub radius “R1h” is fixed by
the rotodynamic requirement. This is basically controlled by operating range of
compressor stage as reducing the inlet shroud radius “R1s” drastically will result in
chocking at higher flow. The present subject matter has the inlet shroud radius of
72.5% for the flow range of 70% to 130% of design flow.

[0052] Yet another embodiment of the present subject matter describes the
impeller blade width at exit ‟B2” (as shown in fig. 6) plays major role in
achieving the overall efficiency of compressor stage. The impeller blade exit
width “B2” influences diffusion, flow associated problems, such as re-circulation,
separation and low momentum zones. The impeller exit blade width “B2” is
directly related to impeller exit blade angle ‟β2b” and flow coefficient of fluid.
Increasing the impeller width demands higher pinching in the diffuser width in
order to avoid flow associated problems like recirculation, separation, and low
momentum zones in the diffuser, and further downstream. The diffuser pinching
in the width is more than 25% which can cause flow disturbance at the diffuser
inlet. Further, impeller exit blade width “B2” has outer diameter in range 315 mm
to 630 mm with impeller exit blade width as 16% - 17% of impeller exit diameter.
For example, in the present subject matter, impeller blade exit diameter is 450 mm
where the flow co-efficient is high with the impeller exit blade angle (-) 40o and
the impeller exit blade width is 38 mm.
[0053] Fig. 16 illustrates impeller blade passage area distribution from inlet to
exit of the impeller along impeller meridional path length, in accordance with an
embodiment of the present subject matter. The impeller passage area distribution
is mainly responsible for diffusion of the fluid within the impeller. The impeller
passage area distribution varies from high flow to low flow stages. Further,
continuous increase in the impeller passage area from impeller inlet to impeller
exit along the meridional flow path ensures conversion of kinetic energy in to
pressure; and also eliminates recirculation zones within the impeller. The impeller
passage area distribution for achieving the higher efficiency for present subject
matter which is of high flow coefficient is shown in Fig. 11. The impeller passage
area “PA” distribution along the percentage length of meridional flow path “A” is
governed by Equation.9.


[0054] Fig. 11 illustrates impeller blade lean angle distribution from inlet to exit
of the impeller along impeller meridional flow path length, in accordance with an
embodiment of the present subject matter. The impeller blade lean angle “L”
influences the induced centrifugal stresses in the impeller. However, blade lean
angle also influences manufacturability of impeller particularly the shrouded
impellers and also plays important role in flow behaviour within the impeller and
at the downstream. The blade lean angle at inlet is 10o deg. and at exit is 25o deg.
with peak at 25% and minimum at 75% of the meridional flow path having
variation like sleeping "S" shape. The blade lean angle variation adopted for the
present subject matter which has enabled to achieve the good flow behaviour
while limiting the stresses within the allowable limit has been shown in Fig.
12.The impeller blade lean angle “L” distribution along the percentage length of
meridional flow path “A” is governed by Equation.10.

[0055] In the present subject matter, impeller geometrical parameters along the
meridional flow path from impeller inlet to impeller exit like Blade angle, Wrap
angle, Slope, Curvature, Passage area, Inlet hub radius, Inlet shroud radius,
Impeller blade exit width, Impeller blade circumferential pitch are finalized based
on systematic design approach with the rich experience of compressor design and
extensive computational fluid dynamics (CFD) analysis and performance testing
of prototype where the efficiency achieved is very close to the theoretical
efficiency.
[0056] Conventionally, no information is available regarding the blade angle
distribution, wrap angle distribution, slope distribution, curvature distribution and
passage area distribution from impeller inlet to impeller exit is also not defined.
Further, no information and geometrical parameters are also available regarding
the impeller inlet hub radius and shroud radius. From the above explained
geometrical parameters, the impeller central blade loading and relative velocity
distribution is known.

[0057] Fig. 12 illustrates impeller blade to blade loading distribution of the
impeller, in accordance with an embodiment of the present subject matter.
Further, blade to blade loading is defined as the ratio of difference in relative
velocities to the average velocity of the suction and pressure side of the impeller.
Flat central loading which is mostly preferred has been achieved in the present
aspect. There is slight unload for the 5% of meridional flow path length which is
acceptable for high flow impellers.
[0058] Fig. 13 illustrates relative velocity distribution on the impeller blade at
both suction and pressure surfaces at hub and shroud sections of the impeller, in
accordance with an embodiment of the present subject matter. Further, the relative
velocity is more at impeller inlet & exit with lower values in the central zone
between 15% and 75% of the impeller meridional flow path length. These are the
major factors influenced the relative velocity distribution, blade loading,
diffusion, static pressure distribution, flow behaviour within the impeller and
further downstream which ultimately results in higher efficiency of compressor
stage. From the rigorous CFD studies, it has been revealed that scaling of impeller
up to 40% upward and 40% downward can the give the same performance while
the ratios of other impeller geometrical parameter are maintained.
[0059] Diffusion is achieved in the impeller from impeller inlet to exit along the
length of meridional flow path in terms of pressure recovery coefficient is
presented in the Fig. 14 (a) and Fig.14 (b). Pressure recovery co-efficient is
defined as the ratio of gain in static pressure to inlet dynamic head. The maximum
pressure recovery co-efficient is 0.72 at the hub on pressure surface of the blade.
Average pressure recovery co-efficient gradually increasing from impeller inlet to
middle portion and gradually decreasing towards impeller exit ensures smooth
pressures recovery without any acceleration within the impeller. Further, pressure
recovery coefficient is defined as the ratio of gain in static pressure to the inlet
dynamic head.
[0060] Similarly, static pressure recovered on both the pressure side and suction
of the impeller blade is presented in the Fig. 15 (a) and Fig.15 (b). Pressure

recovery on both pressure & suction surface of the impeller blade along the
meridional flow path length of the impeller without any chattering or jig jag
pattern ensures smooth pressure recovery and flow behavior.
[0061] Although embodiments for the present subject matter have been described
in language specific to structural features, it is to be understood that the present
subject matter is not necessarily limited to the specific features described. Rather,
the specific features and methods are disclosed as embodiments for the present
subject matter. Numerous modifications and adaptations of the
system/device/structure of the present invention will be apparent to those skilled
in the art, and thus it is intended by the appended claims to cover all such
modifications and adaptations which fall within the scope of the present subject
matter.

We claim:
1. A 3D impeller of centrifugal compressor stage with high flow coefficient
for compressing fluid with high aerodynamic efficiency, the 3D impeller
comprises:
a rotor;
a hub disc (1) connected to the rotor, wherein the hub disc is covered
by a shroud disc (3);
a plurality of blades radially protruding from the hub disc (1) and
spaced equidistantly on circumference of the hub disc (1), wherein the plurality of
blades are disposed between the hub disc (1) and the shroud disc (3); and
wherein blade angle distribution at inlet and exit of impeller at the
hub disc (1) is (-) 51o deg. and (-) 40o deg. respectively with maximum
angle (-)10o deg at 50% of meridional flow path length.
2. The 3D impeller of centrifugal compressor stage as claimed in claim 1,
wherein impeller blade angle distribution at inlet and exit of impeller at the shroud
disc (3) is (-) 55o deg. and (-) 40o deg. respectively with maximum angle (-) 37o
deg at 75% of the meridional flow path length.
3. The 3D impeller of centrifugal compressor stage as claimed in claim 1,
wherein impeller wrap angle distribution at the shroud disc (3) decreases
uniformly in range from 0.0o deg. to (-) 40o deg. and at the hub disc (1) is in range
from (-) 5o to (-) 45o deg.
4. The 3D impeller of centrifugal compressor stage as claimed in claim 1,
wherein impeller shroud disc contours (4) slope varying uniformly in range from
0.0o deg. at inlet to 75o deg. at exit and the hub contours (2) slope varying
uniformly in range from 14o deg. at inlet to 90o deg. at exit.
5. The 3D impeller of centrifugal compressor stage as claimed in claim 1,
wherein the impeller further comprises blade curvatures hub and shroud contours
influences the blade loading, relative velocity distribution, pressure rise and there
by efficiency. Variation in curvature that has resulted higher efficiency in the
present invention at hub & shroud surface

6. The 3D impeller of centrifugal compressor stage as claimed in claim 1,
wherein the impeller further comprises impeller inlet hub radius with outer
diameter in range of 315 mm to 630 mm with impeller inlet hub radius as 37% -
39% of impeller outer diameter and inlet shroud radius as 70% - 72% of impeller
outer diameter.
7. The 3D impeller of centrifugal compressor stage as claimed in claim 1,
wherein the impeller further comprises impeller blade lean angle which is 10° deg
at inlet and 25° deg at exit, wherein maximum of the impeller blade lean angle is at
25% and minimum is at 75% of the impeller meridional flow path length which
has variation like "S" shape.
8. The 3D impeller of centrifugal compressor stage as claimed in claim 1,
wherein the impeller further comprises an impeller exit blade width "B2" which
has outer diameter in range 315 mm to 630 mm with impeller exit blade width as
8.5% - 9.5% of impeller exit diameter.
9. The 3D impeller of centrifugal compressor stage as claimed in claim 1,
wherein circumferential pitch of the plurality of blades is in range 24° to 21° deg.