SHROUDED 3D IMPELLER FOR MULTI-STAGE CENTRIFUGAL
COMPRESSOR WITH MEDIUM FLOW COEFFICIENT
FIELD OF INVENTION:
[001] The present subject matter described herein, relates to a 3D impeller of
multi-stage centrifugal compressor with medium 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 medium flow coefficient ranging from 0.055
to 0.062 of multi-stage centrifugal compressor.
BACKGROUND AND 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. The plurality of vanes is
disposed between the disk 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. The geometric configuration of rotor blading significantly
affects aerodynamic efficiency of the compressor, due to the fact that the
geometric characteristics of the blade 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 6715991B2, dated 05/04/2004 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. 1 illustrates the design of impeller of
the present US patent. The suction and pressure surface of the vane referred a
convex and concave surface respectively. The impeller blade geometry
coordinates are fixed and are given in Cartesiair co-ordinates in terms of impeller
exit radius which is 200 mm.

[004] 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. 2 illustrate the impeller of
present US patent. In the present US patent, the impeller is of open impeller
without shroud disc generally of single stage of very high operating tip speed
generally 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.
[005] US patent no. US 5,158,435 dated 13/11/2012 titled "Impeller stress
improvement through over-speed" describes a method for improving the
capability of a body to withstand stress experienced during rotation by inducing at
a selected location in the body a residual compressive stress which opposes the
steady tensile stress experienced at the selected location during rotation of the
body. Fig.3 illustrates cross section of the impeller. The present US patent is
purely related to improving the impeller mechanical strength by inducing
localized residual stresses in the impeller.
[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 cf the blade.

[007] One of the main demands from all the 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

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 along the meridional flow
path from the impeller inlet to impeller exit to achieve high aerodynamic
efficiency in the multi-stage compressor.
[009] Another object of the present invention is to provide geometrical
parameter, i.e., blade wrap angle of 3D impeller along the meridional flow path
from the impeller inlet to impeller exit to achieve high aerodynamic efficiency in
the multi-stage compressor.
[0010] Another object of the present inversion is to provide geometrical
parameter, i.e., blade curvature at hub and Shroud of 3D impeller along the
meridional flow path from the impeller inlet to impeller exit to achieve high
aerodynamic efficiency in the multi-stage compressor.
[0011] Another object of the present invention is to provide geometrical
parameter, i.e., passage area distribution in 3D impeller along the meridional flow
path from the impeller inlet to impeller exit to achieve high aerodynamic
efficiency in the multi-stage compressor.
[0012] Another object of the present invention is to provide geometrical
parameter, i.e., an inlet hub radius of 3D impeller along the meridional flow path

from the impeller inlet to impeller exit to achieve high aerodynamic efficiency in
the multi-stage compressor.

[0013] Another object of the present invention is to provide geometrical

parameter, i.e., an inlet shroud radius of 3D impeller along the meridional flow
path from the impeller inlet to impeller exit to achieve high aerodynamic
efficiency in the multi-stage compressor.

[0014] Yet another object of the present invention is to provide geometrical

parameter, i.e., blade lean angle of 3D impeller along the meridional flow path
from the impeller inlet to impeller exit to achieve high aerodynamic efficiency in
the multi-stage compressor.
[0015] Yet another object of the present invention is to provide geometrical
parameter, i.e., blade width at exit of 3D impeller along the meridional flow path
from the impeller inlet to impeller exit to achieve high aerodynamic efficiency in
the multi-stage compressor.
SUMMARY OF THE INVENTION;

[0016] 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 with respect to meridional plane at inlet and exit
of impeller at the hub disc (1) is (-) 57° deg. and (-) 48° deg. respectively with
maximum angle location is at 50% of meridional flow path length. Further, the
present 3D impeller adopts appropriate Bladri 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.
[0017] 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
[0018] 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 sUme 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: i
[00191 Fig.l, Fig. 2, Fig. 3, and Fig. 4 illustrate the view of the impeller of
centrifugal compressor known in the art; .<
[0020] Fig. 5 illustrates a 3D view of impeller paving twisted 3D impeller blade,
in accordance with an embodiment of the preseft subject matter;
[0021] Fig. 6 illustrates cross sectional view of the impeller with shroud disc, in
accordance with an embodiment of the present subject matter;
[0022] 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; ;;
[0023] 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; ,'.
[0024] 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; ^

[0025] Fig. 10 illustrates impeller blade curvatu-e distribution from inlet to exit at
i
hub and shroud surfaces of the impeller, in accordance with an embodiment of the
present subject matter;
[0026] Fig. 11 illustrates impeller blade passage area distribution from inlet to
exit of the impeller along impeller meridional' flow path length, in accordance
with an embodiment of the present subject matter;
[0027] Fig. 12 illustrates impeller blade lean angle distribution from inlet to exit
of the impeller along impeller meridional flow |»ath length, in accordance with an
embodiment of the present subject matter; J
[0028] Fig. 13 illustrates impeller blade to Itlade loading distribution of the
impeller, in accordance with an embodiment of fhe present subject matter;
*; .
[0029] Fig. 14 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;
[0030] Fig. 15 (a) and (b) illustrate 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; and ,
[0031] Fig. 16 (a) and (b) illustrate static pressure distribution on the blade
suction and pressure surfaces at hub and shroud sections of the impeller, in
accordance with an embodiment of the present s abject matter.
[0032] The figures depict embodiments of tKe 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:
[0033] The subject matter disclosed herein relates to 3D impeller of centrifugal
compressor stage with medium flow coefficient. In the centrifugal compressor

fluid is compressed to a desired pressure and eaters 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 rhen enters the next stage impeller
for further compression. The pressurized gas frop the last stage impeller goes into
a volute/collector chamber that concentrically arranged inside the inter-stage duct
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 i blade circumferential pitch are
achieved along the meridional flow path for higii aerodynamic efficiency. The 3D
impellers are made according to achieved geometrical parameters which gave
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.
k
[0034] 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 aerodyflamic 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 angl£ 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 afigle distribution at hub along the
meridional flow path has greater effect on? the aerodynamic efficiency as
compared to blade angle distribution at the shroM.
[0035] Further, centrifugal compressors with 3p 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 s>f the compressors where in the
energy is added to the working fluid playf 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 vtithout flow recirculation, flow
separation, low momentum zone in the entire ffow path of compressor stage. This
is achieved by adopting appropriate Blade tangle distribution, Wrap angle
distribution, Passage area distribution, Slope & Curvatures at hub and shroud
sections from inlet to exit of impeller. [0036J As explained above in the problem in prior art section, the efficiency of
the impeller is low, and there are more frictio^al losses and less blade loading.
Design and structure of the impeller is not capable to achieve the high efficiency.
Geometrical parameters of the impeller, knov/n in the prior art, provide less
efficiency and more frictional losses. :[0037] According to an implementation of the present subject matter, an impeller
blade angle "J$" 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 flov? 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. jThe 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. i
[0038J It should be noted that the description^ and figures merely illustrate the
principles of the present subject matter. It should be appreciated by uiose 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 tte principles of the present subject

matter and are included within its spirit and ixope. Furthermore, all examples
recited herein are principally intended expressly to be for pedagogical purposes to
aid the reader in understanding the principles oifthe 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 organisation 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. jj
[0039] 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 tht; 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 iicluded within its scope.
[0040] Fig. 5 illustrates top view of 3D impeller, in accordance with the present
subject matter. 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 and shroud disc 1 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, th^ 3D impeller has a plurality of
blades/vanes 5 (in fig. 6 cross section of one V>lade of the impeller is shown for
clarity) supported by the hub disc I and radially protruding from the disc. The
plurality of blades 6 is circumferentially and iequidistantly 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 passagi 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 disk and the shroud and the vanes. The width of the Impeller
blade DIV plays major role in achieving the overall efficiency of compression
stage. Impeller inlet hub radius "Rih" in centrifugal compressor stage affects the
roto-dynamic behaviour of the compressor. In the centrifugal compressor, higher
inlet hub radius "Rih" demands higher inlet shibud radius "Ris" which increases
the inlet relative velocity at shroud. {0041] 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. 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 flov£ 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 impeller blade angle variation
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 I

[0042] Further, 3D impeller of centrifugal compressor stage with blade angle
distribution at inlet is (-) 57 deg. and at exit is'(-) 48 deg. of impeller at hub disc
(1). The maximum angle location of the blade angle distribution at hub disc (1) is
at 50% of meridional flow path length. Furthermore, the impeller blade angle
distribution at inlet is (-) 53 deg. and at exit i$ (-) 48 deg. of impeller at shroud
disc. The maximum angle location of the blads angle distribution at the shroud
k
disc (3) is at 75% of meridional flow path length.

[0043] 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. The Impeller wrap angb "6" 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. The present subject matter explains £he wrap angle distribution which
decreases uniformly from impeller inlet to irApeller exit for achieving higher
efficiency as shown in Fig. 8. Numerically the ^vrap angle variation is in range of
0.0° deg. to (-) 52.5° deg. for shroud; and (-) 3.|° to (-) 55° deg. for the hub with
respect to the meridional plane or meridional flow path. The impeller wrap angle
variation at the hub and the shroud sections! along the percentage length of
meridional flow path "A" is governed by Equati )n.3 and Equation.4 respectively.
For Hub

[0044] 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 aid shroud disc contours slopes
influence the blade loading, relative velocity distribution, pressure rise and there
by overall efficiency of the impeller. Variation 'n slope with respect to meridional
plane at hub & shroud surface is shown in ifig.9. The present subject matter
explains the slope of 0.0° deg. at inlet and 85.5? deg. at exit at the shroud surface
where as the slope is 20° deg. and 90° deg. at hub surface of the impeller. The
variation of the slope of impeller "S" at hub and shroud sections along the
percentage length of meridional flow path "Af is governed by Equation.5 and
Equation.6 respectively.

At Hub
S = 20.8214 + 0.664819 * A + 0.00639645 *A2 + 0.0000593961 * A3-2.16183
"10"6* A* + 6.98271*10"9* A5 +2.55773* 10"" *]A6 — Eq.5
At Shroud ,
j
S = 0.951088 + 1.03898* A -0.0002091JB6 *A2 + 0.000862715* A3-
0.0000259523* A4 + 2.61747*10"7* A5 -9.0224^ *10~10 * A6 — Eq.6
[0045] 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. The curvatures of hr?peller blade at hub and shroud
contours influences the blade loading, relative velocity distribution, pressure rise
and there by overall efficiency of the impeller* Variation in curvature results in
higher efficiency in the present subject matte?- at hub and shroud surfaces are
shown in Fig. 10. Hub curvature at impelle|; inlet & exit is 0.005 & 0.0
respectively and the maximum curvature is 0.0^ (1/mrn) located between the 20%
to 50% of meridional length. The impeller curvatures "C" variation at hub and
shroud sections along the percentage length pf meridional flow path "A" is
governed by Equation. 7 and Equation. 8 respectively.
At Hub "
C = 0.000936155*A - 0.0000810948 * A2 + 3.84697* 10"6* A3- 1.00796*10"7 *A4
+ 1.51416*10"9*A5- 1.3347*10""* A6+ 6.555IS* 10-14* A7 - 1.40461*1016* A8+
0.00481709 I — Eq.7
it
At Shroud
C - 0.00045609 * A - 0.0000541067. * A2 + 5.45625* 10"6* A3
- 2.41063*10'7* A4 + 5.19658*10'9*;; A5- 5.92713*10-" * A6
+ 3.46607* 10"13* A7-8.22639*10"16*A8 +0.01 JJ1762 — Eq.8
[0046] Other embodiment of the present subjept matter explains circumferential
pitch of the impeller blades in terms of degre? depends of 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
behaviour in the entire compressor stage. For ths present subject matter which is a
medium flow impeller, the circumferential pitch'is in range of 24° deg. to 21° deg.
for achieving better blade loading and lesser friction losses which has ultimately
resulted higher efficiency.
I
(0047] Another embodiment of the present subject matter relates to impeller inlet
hub radius DRu," in a centrifugal compressor stage. Where higher inlet hub radius
"Rii,"demands higher inlet shroud radius which increases the inlet relative
i
velocity at the shroud. The Inlet tip velocity reduces the impeller diffusion rate
and accordingly pressure recovery and impeller efficiency. Inlet hub radius
"Rih"also influences every stage of the centrifiigal 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. *
[0048] Furthermore, the Impeller inlet shroud rfidius ORisw (as shown in fig. 6) is
free to increase or decrease whereas the htb radius "Rth" is fixed by the
rotodynamic requirement. This is basically Controlled by operating range of
compressor stage as reducing the inlet shroud radius "Ru" drastically will result in
chocking at higher flow. The present subject mitter has the inlet shroud radius of
61% for the flow range of 70% to 130% of design flow.
[0049] Yet another embodiment of the present subject matter describes the
impeller blade width at exit Diy (as showii 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 like re-circulation,
separation & low momentum zones. The impeller exit blade width "B2" is directly
related to impeller exit blade angle DpV' 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, seprj-ation, and low momentum zones
in the diffuser and further downstream. The diffuser pinching in the width more
than 25% can cause flow disturbance at the diffuser inlet. For example, in the
present subject matter, impeller blade exit diameter is 450 mm where the flow co-
efficient is medium with the impeller exit blade £ngie (-) 48° and the impeller exit
blade width is 25.6 mm. 1
[0050] Fig. 11 illustrates impeller blade passage area distribution from inlet to
exit of the impeller along impeller meridional rjath length, in accordance with an
embodiment of the present subject matter. The iknpeller passage area distribution
is mainly responsible for diffusion of the fluid -within the impeller. The impeller
passage area distribution varies from high flyw 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 medium flow coefficient i£ shown in Fig. 11. The impeller
passage area "PA" distribution along the percentage length of meridional flow
path "A" is governed by Equation.9. ;
PA = (-) 0.00214781*A + 0.000204239*A2-9.8()207*106*A3 + 2.67238*10"7* A4
-0.0417*10-9*A5 + 2.76297*10ll*A6 + 3.846^*l0-'4*A7-1.65977*10-,5*A8
+ 6.80386* 10"l8A9 + 0.0265937 [ — Eq.9
[0051] Fig. 12 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
influences the induced centrifugal stresses in tie 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 10° deg. and at exit is 25° deg.
with peak at 25% and minimum at 75% of Ihe meridional flow path having

variation like sleeping "S" shape. The blade Wn 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.
i
■
[0052] 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
k
efficiency. >
[0053] Conventionally, no information is available regarding the blade angle
distribution, wrap angle distribution, slope distribution, curvature distribution and
passage area distribution from impeller inlet td impeller exit is also not defined.
Further, no information and geometrical parameters are available regarding the
impeller inlet hub radius and shroud radius. Frorh the above explained geometrical
parameters, the impeller central blade loading £nd relative velocity distribution is
known. .;;
[0054] Fig. 13 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.
Central loading which is mostly preferred has teen achieved in the present aspect.
Fig. 14 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 minimum at impeller inlet & exit with lower values in the central zone
between 20% to 70% of the impeller meridion^ path length. These are the major
factors influenced the relative velocity distribution, blade loading, diffusion, static
pressure distribution, flow behaviour within th< impeller and further downstream
which ultimately results in higher efficiency; of compressor stage. From the
rigorous CFD studies, it has been revealed thkt scaling of impeller up to 40%
upward and 40% downward can the give the saroe performance while the ratios of
other impeller geometrical parameter are maintained.
[0055] 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. 15 (a) and Fig. 15 (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 0.65 at the hut- 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 £*ain in static pressure to the inlet
dynamic head. Similarly, static pressure recovered on both the pressure side and
suction of the impeller blade is presented in?, the Fig. 16 (a) and Fig. 16 (b).
Pressure recovery on both pressure & suction s'irface 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 flaw behavior.
[0056] 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 disclose;! as embodiments for the present
subject matter. Numerous modification?; 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. s

We claim:
1. A 3D impeller of centrifugal compressor stage 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 (I) and the shroud disc (3); and
wherein blade angle distribution at inlet and exit of impeller at the
hub disc (1) is (-) 57° deg. and (-) 48° deg. respectively with maximum
angle location is at 50% of meridional flow path length.
2. The 3D impeller of centrifugal compressor stage as claimed in claim 1,
ij
wherein impeller blade angle distribution at inle and exit of impeller at the shroud
disc (3) is (-) 53° deg. and (-) 48° deg. respectively with maximum angle location
is 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 0.0° deg. to (-) 52.5° deg. and at the hub disc (1) is in
range from (-) 3.5° to (-) 55° 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
0.0° deg. at inlet to 85.5° deg. at exit and the hub contours (2) slope varying
uniformly in range from 20° deg. at inlet to 90° iieg. 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 as 37% - 39% of impeller outer diameter
and inlet shroud radius as 60% - 62% 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 sleeping "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 as in range 5.55% to 5.75% 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.