Computational analysis of centrifugal compressor with grooves on casing

International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN
0976 – 6359(Online), Volume 6, Issue 2, February (2015), pp. 01-09© IAEME
1
COMPUTATIONAL ANALYSIS OF CENTRIFUGAL
COMPRESSOR WITH GROOVES ON CASING
P. Usha Sri*, J. Deepthi Krishna**
*Professor, Department of Mechanical Engineering, University College of Engineering, Osmania
University, Hyderabad, Telangana – 500 007, India.
**Student, Department of Mechanical Engineering, University College of Engineering, Osmania
University, Hyderabad, Telangana – 500 007, India.
ABSTRACT
Computational results of flow field in a centrifugal impeller with grooves on casing are
presented in the paper. A low speed centrifugal compressor with 2% tip clearance is considered.
Analysis is carried out for three different cases, one without grooves on the casing, second with two
grooves on casing and third with three grooves on the casing. The three cases are studied at five
different flow coefficients φ=0.28, 0.34, 0.42 (design value), 0.48 and 0.52 using Ansys-CFX. Pressure
ratio improvement with two grooves on casing is observed. The leakage of flow over tip of the blade
through the grooves from pressure side to suction side of the blade is interacting with passage wake near
casing and reduction in passage wake region area is observed with two grooves on casing. Increase in
the velocity of the fluid in passage wake is also observed with two grooves on casing. Increase in
pressure ratio is observed for the casing with two grooves at all flow coefficients. For three grooves on
casing also, increase of velocity in passage wake is observed but reduction in pressure ratio is observed
due to more leakage flow. Reduction in pressure ratio for all flow coefficients is observed with three
grooves on casing.
Key Words: Centrifugal Compressor, Flow coefficient, Grooves on casing, passage wake.
1. INTRODUCTION
In turbomachines, to desensitize tip clearance effects, squealer tips / partial shrouds, tip geometry
modifications, casing treatment etc. are suggested in the literature. P. Usha Sri and N. Sitaram observed
that the impeller with the chamfer on suction surface of the blade tip shows small improvement in
INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING AND
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ISSN 0976 – 6340 (Print)
ISSN 0976 – 6359 (Online)
Volume 6, Issue 2, February (2015), pp. 01-09
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performance. With an increase in the chamfer dimension on suction surface of blade tip, performance
improvement is observed. Through experiments, N. Sitaram and S.M. Swamy have observed
performance improvement on centrifugal compressor with pressure side partial shrouds. S. Senthil and
N. Sitaram studied the performance of a centrifugal compressor by means of squealer tips. They
observed increase in energy coefficient and efficiency with squealer tips on pressure surface. S. Senthil
and N. Krishna Mohan found that sloping type squeeler tip has beneficial effects. Chi-Young Park et. al
have observed improvement of performance and surge margin with ring groove system on centrifugal
compressor. Fayez M. Wassef et. al have conducted experiments on centrifugal compressor and
observed improvement in limit of stability with addition of a ring and a groove in the casing in diffuser
region.
2. COMPUTATIONAL METHODOLOGY
The design details of the impeller which is used in the investigations are given below:
Inducer hub diameter, d1h = 160 mm Inducer tip diameter, d1t = 300 mm
Impeller tip diameter, d2 = 500 mm Blade height at the exit, b2 = 34.7 mm
No. of blades of impeller, Nb = 16 Blade angle at inducer hub, β1h= 53
o
Blade angle at inducer tip, β1t = 35
o
Blade angle at exit, β2 = 90
o
Thickness of the blade, t = 3 mm Rotor speed, N = 2000 rpm
All angles are with respect to the tangential direction.
Centrifugal impeller with above specifications with 3 mm thickness throughout the blade, 2% tip
clearance is shown in Fig. 1. Assuming periodicity, single passage of centrifugal impeller is analysed. A
single passage of the impeller with inlet at 50 mm ahead of the impeller and outlet at a distance of 35
mm downstream of impeller is shown in Fig. 2. Casing is designed with a clearance of 0.7 mm
throughout the blade height. Total pressure is used for inlet boundary condition and mass flow rate at
outlet. Rotating frame of reference is given to the domain. ANSYS-CFX software is used for obtaining
the solution and standard k-ε turbulence model is used for the closure. The centrifugal compressor is
analysed at five different flow coefficients (0.28, 0.34, 0.42, 0.48 and 0.52), the design flow coefficient
being 0.42.
Fig. 1 Centrifugal compressor

International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976
0976 – 6359(Online), Volume 6, Issue
On casing of the impeller, circular grooves of width 3
cases of centrifugal compressor, one without gr
locations of 0.515, 0.555 and third with three grooves on casing
0.595 are modeled as shown in figure 3 to 5. Grid with boundary condit
shown in figures 6-8.
Fig. 3 Compressor without
grooves on casing grooves on casing grooves on casing
Fig. 6 Compressor without
6359(Online), Volume 6, Issue 2, February (2015), pp. 01-09© IAEME
3
Fig. 2 Computational domain of single passage
On casing of the impeller, circular grooves of width 3 mm and depth 4 mm are made. Three
cases of centrifugal compressor, one without grooves, second with two grooves on casing
and third with three grooves on casing at streamwise locations of 0.515, 0.555,
are modeled as shown in figure 3 to 5. Grid with boundary conditions for three different
Fig. 4 Compressor with two Fig. 5
Fig. 7 Compressor with two Fig. 8
Computational domain of single passage
mm and depth 4 mm are made. Three
ooves, second with two grooves on casing at streamwise
at streamwise locations of 0.515, 0.555,
ions for three different cases is
Fig. 5 Compressor with three
Fig. 8 Compressor with three

3. RESULTS AND DISCUSSIONS
A low speed centrifugal compressor of radial blades with g
pressure contours, velocity contours on the casing of the compressor are plotted for flow coefficient of
0.34. Velocity vectors, total pressure contours
plane at a streamwise location of 0.62. Pressure variation along streamwise direction, pressure ratio at
all flow coefficients and percentage deviation in velocity along streamwise direction with grooved
casing are presented.
3.1 Static Pressure Contours on
Pressure contours on casing for three cases, without grooves on casing, with two grooves on
casing and with three grooves on casing is shown in figures 9
rise from inlet to outlet of the compressor due to dynamic action of the rotating impeller. Pressure
gradient above the blade is observed due to the high pressure on pressure side and low pressure on
suction side of the blade. For the casing with two
For the casing with three grooves
observed due to more leakage of flow from the grooves.
Fig. 9 Pressure contours on
casing without grooves
3.2 Velocity Contours on Casing
Velocity contours on casing for t
show gradual increase of velocity from inlet to outlet of the impeller.
pressure side of the blade to suction side is observed
Fig. 12 Velocity contours on
casing without grooves
4
3. RESULTS AND DISCUSSIONS
A low speed centrifugal compressor of radial blades with grooves on casing
0.34. Velocity vectors, total pressure contours and static pressure contours are plotted on
of 0.62. Pressure variation along streamwise direction, pressure ratio at
ontours on Casing:
casing and with three grooves on casing is shown in figures 9-11. The contours show gradual pres
suction side of the blade. For the casing with two grooves, no significant change in pressure is observed.
ing with three grooves, low pressures on both pressure and suction side of the blade is
observed due to more leakage of flow from the grooves.
Fig. 10 Pressure contours on Fig. 11
casing with two grooves casing with three grooves
asing
asing for three different cases are shown in figures 12
show gradual increase of velocity from inlet to outlet of the impeller. Fluid flow with low velocity from
pressure side of the blade to suction side is observed through grooves.
Fig. 13 Velocity contours on Fig. 14
casing with two grooves casing
rooves on casing is analysed. The
urs are plotted on a meridional
of 0.62. Pressure variation along streamwise direction, pressure ratio at
11. The contours show gradual pressure
change in pressure is observed.
, low pressures on both pressure and suction side of the blade is
casing with three grooves
s are shown in figures 12-14. The contours
luid flow with low velocity from
casing with three grooves

3.3 Static pressure Contours at Meridional P
Pressure contours at a meridional plane
15-17. The contours show high pressure on pressure side
(SS) of the blade. With two grooves on casing, a slight pressu
three grooves on casing, significant
meridional plane for without
grooves on casing
3.4 Total Pressure Contours at M
Total pressure contours on meridional plane
figures 18-20. On suction side near casing,
observed. With two grooves on casing, low total pressure area of passage wake is reduced. The leakage
flow from the grooves is interacting with passage wake. With three grooves on casing, the passage wake
area is further reduced, but total pressure in this area is much lower due to more leakage of flow from
three grooves.
Fig. 18 Total pressure
contours on meridional plane
for without grooves on casing
3.5 Velocity Contours at Meridional
Velocity contours on meridional plane for three cases are shown in figure 21
show improved velocities on suction side
side of the blade is reducing with two grooves and t
passage wake region is much lower with three grooves on casing as more leakage flow
with the main flow.
PS SS
PS SS
5
ressure Contours at Meridional Plane
contours at a meridional plane just after the grooves for three cases is shown in figures
17. The contours show high pressure on pressure side (PS) of the blade, low pressure on suction side
of the blade. With two grooves on casing, a slight pressure drop is observed on suction side. With
significant reduction in pressure on suction side is observed
meridional plane for impeller
with two grooves on casing
Fig. 17
with three grooves on casing
Meridional Plane
Total pressure contours on meridional plane just after the grooves for three cases are shown in
near casing, low total pressure area caused due to passage wake is
ooves is interacting with passage wake. With three grooves on casing, the passage wake
reduced, but total pressure in this area is much lower due to more leakage of flow from
contours on meridional plane
for impeller with two grooves
on casing
contours on impeller with
three grooves on casing
Velocity Contours at Meridional Plane
Velocity contours on meridional plane for three cases are shown in figure 21
on suction side with grooves. The low velocity passage wake area on suction
side of the blade is reducing with two grooves and three grooves on casing. However, the velocity in
passage wake region is much lower with three grooves on casing as more leakage flow
PS SS
PS SS
after the grooves for three cases is shown in figures
of the blade, low pressure on suction side
re drop is observed on suction side. With
observed.
for three cases are shown in
low total pressure area caused due to passage wake is
ooves is interacting with passage wake. With three grooves on casing, the passage wake
reduced, but total pressure in this area is much lower due to more leakage of flow from
contours on impeller with
three grooves on casing
Velocity contours on meridional plane for three cases are shown in figure 21-23. The contours
with grooves. The low velocity passage wake area on suction
hree grooves on casing. However, the velocity in
passage wake region is much lower with three grooves on casing as more leakage flow is interacting
PS SS
PS SS

grooves on casing
3.6 Velocity Vectors at Meridional P
Velocity vectors on meridion
with low velocity is observed on suction side
reduction in passage wake area is observed.
Fig. 24 Velocity vectors on
grooves on casing
3.7 Static Pressure Contours at
Pressure contours in blade to blade view, at span 0.7 is shown in figures 27
show gradual pressure rise from inlet to outlet of the compressor due to dynamic action of the rotating
impeller. With two grooves on casing,
the pressure at outlet is reduced.
Fig. 27 Pressure contours for
without grooves on casing
PS SS
PS SS
6
Fig. 23
ional Plane
Velocity vectors on meridional plane for three cases are shown in figure
with low velocity is observed on suction side near casing of the blade. With grooves on casing,
reduction in passage wake area is observed.
Fig. 26
ontours at Span 0.7
Pressure contours in blade to blade view, at span 0.7 is shown in figures 27
With two grooves on casing, no pressure change is observed. But with three groves on casing,
impeller with two grooves on
casing
Fig. 29
im
PS SS
PS SS
al plane for three cases are shown in figures 24-26. Passage wake
of the blade. With grooves on casing,
Pressure contours in blade to blade view, at span 0.7 is shown in figures 27-29. The contours
hange is observed. But with three groves on casing,
impeller with three grooves
on casing
PS SS
PS SS

101000
101500
102000
102500
103000
0 0.5
no
groove
3.8 Velocity Contours at Span 0.7
Velocity contours in blade to blade view, at span 0.7 is shown in figures 30
show low velocity region on suction side of the blade. With grooves on casing, the l
is reducing and also velocity improvement is observed.
Fig. 30 Velocity contours for
without grooves on casing
3.9 Static Pressure Distribution
Static pressure distribution along streamwise direction from inlet to outlet is shown in figure 33.
This plot elucidate that the pressure from inlet to the outlet of the compressor is increa
along the stream wise direction due to the dynamic head developed by the rotating impeller.
static pressure near streamwise direction of 0.2 is observed for all cases due to the acceleration of the
flow in to the eye of the impeller. Static pressure reduction is observed with the grooves on casing near
the location of grooves. But after the grooves location, static pressure is almost equal to the casing
without grooves. With two grooves on casing, static pressure at outlet is more t
casing without grooves.
3.10 Total Pressure Distribution
Total pressure distribution along streamwise direction
Gradual increase of pressure along streamwise direction
observed. Total pressure improvement
through grooves from pressure side to suction side
suction side of the blade. Though pressure change is not significant, substantial velocity improvement is
the cause for total pressure rise around the grooves location.
Stream wise location
Fig. 33 Static Pressure from inlet to outlet
StaticPressure
7
1 1.5
pan 0.7
Velocity contours in blade to blade view, at span 0.7 is shown in figures 30
show low velocity region on suction side of the blade. With grooves on casing, the l
is reducing and also velocity improvement is observed.
impeller with two grooves on
casing
Fig. 32
impeller with
This plot elucidate that the pressure from inlet to the outlet of the compressor is increa
along the stream wise direction due to the dynamic head developed by the rotating impeller.
r. Static pressure reduction is observed with the grooves on casing near
without grooves. With two grooves on casing, static pressure at outlet is more t
istribution
Total pressure distribution along streamwise direction around the grooves is
along streamwise direction because of dynamic action of the impeller is
observed. Total pressure improvement with grooves is observed. With grooves
pressure side to suction side of the blade is interacting with passage wake on the
the blade. Though pressure change is not significant, substantial velocity improvement is
the cause for total pressure rise around the grooves location.
Stream wise location Stream wise location
re from inlet to outlet Fig. 34 Total Pressure
101600
101800
102000
102200
102400
0.2
no groove
2 grooves
3 grooves
TotalPressure
Velocity contours in blade to blade view, at span 0.7 is shown in figures 30-32. The contours
show low velocity region on suction side of the blade. With grooves on casing, the low velocity region
impeller with three grooves
on casing
This plot elucidate that the pressure from inlet to the outlet of the compressor is increasing gradually
along the stream wise direction due to the dynamic head developed by the rotating impeller. A drop in
r. Static pressure reduction is observed with the grooves on casing near
without grooves. With two grooves on casing, static pressure at outlet is more than the static pressure of
around the grooves is shown in figure 34.
dynamic action of the impeller is
ith grooves on casing, the fluid flow
blade is interacting with passage wake on the
the blade. Though pressure change is not significant, substantial velocity improvement is
Stream wise location
Pressure distribution
0.4 0.6
no groove
2 grooves
3 grooves

8
3.11 Percentage Deviation of Velocity with Grooves
The velocity from inlet to outlet of the compressor passage of grooved casing is compared with
the casing without grooves. Percentage deviation in velocity with two grooves is shown in figure 35.
Near the streamwise location where grooves are present, a significant velocity improvement of 35% is
observed.
Fig. 35 Percentage deviation in velocity from inlet to outlet
3.12 Pressure Ratio at Off Design Conditions
Outlet to inlet pressure ratio at different flow coefficients is shown in fig. 36. Increase in
pressure ratio with two grooves on casing is observed at all flow coefficients. But with three grooves on
casing, reduction in pressure ratio is observed at all flow coefficients because of more fluid leakage
through the three grooves.
Fig. 36 Pressure ratio for different flow coefficients
-5
0
5
10
15
20
25
30
35
40
0 0.2 0.4 0.6 0.8 1
PercentageDeviationinVelocity
Sreamwise Location
1.014
1.0142
1.0144
1.0146
1.0148
1.015
1.0152
1.0154
0.25 0.3 0.35 0.4 0.45 0.5 0.55
StaticPressureRatio
Flow Coefficient
No Groove
2 Grooves
3 Grooves

9
4. CONCLUSIONS
A low speed centrifugal compressor with 2% tip clearance with two grooves on casing and three
grooves on casing are analysed at five different flow coefficients. The results are compared with the
casing without grooves. With three grooves on casing, though velocity at the meridional section around
the grooves is increased, the pressure at outlet is reduced because of more leakage of flow over the
blades from grooves. With two grooves on casing, due to the interaction of the leakage flow from
grooves with passage wake, the velocity and total pressure improvement is observed. Also with two
grooves on casing, static pressure rise at outlet is observed for all coefficients.
5. ACKNOWLEDGEMENTS
The authors acknowledges All India Council for Technical Education (AICTE) for the financial
assistance provided for the project under R&D scheme.
REFERENCES
1. P. Usha Sri and N. Sitaram, Computational Investigation of Flow in a Centrifugal Impeller with
Chamfered Blade Tips: Effect of Tip Clearance, National Conference on CFD Applications in
Power &b Industry Sectors, organised by BHEL R&D, Hyderabad during Nov 17-18, 2006
2. S. Senthil and N. Sitaram, 2002, “Performance Improvement of a Centrifugal Compressor by
means of Squealer Tips”, Proc. of the 4th
ICPF Beijing, China, 26-29.
3. S. Senthil and N. Krishna Mohan, Experimental Investigation on a centrifugal compressor by
means of rectangular, elliptical and sloping squeeler tips, Indian Journal of Science and
Technology, Vol.2, No. 7, July 2009, pp 30-34.
4. Chi-Young Park, Young-Seok Choi, Kyoung-Yong Lee and Joon-Yong Yoon, Numerical Study
on the Range Enhancement of a centrifugal compressor with a ring groove system, Springer,
Journal of Mechanical Science and Technology 26 (5)(2012) 1371-1378.
5. Fayez M. Wassef, Ahmed S. Hassan, Hany A. Mohamed and Mohamed A. Zaki, Stability and
Performance of a Low Speed Centrifugal Compressor with Modified Casing, Journal of
Engineering Sciences, JES, Assiut University, Vol. 32, No. 5, pp. 2025-2047, 2004
6. N. Sitaram and S.M. Swamy, Performance Improvement of a Centrifugal Compressor by Passive
Means, International Journal of Rotating Machinery, Volume 2012, Article ID 727259, 9 pages.
7. P. Usha Sri and J. Deepti Krishna, “Effect of Tip Clearance on A Centrifugal Compressor”
International Journal of Mechanical Engineering & Technology (IJMET), Volume 5, Issue 9,
2014, pp. 379 - 384, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359.
8. Jyothi P.N, A. Shailesh Rao, M.C. Jagath, and K. Channakeshavalu, “Understanding The Melt
Flow Behaviour of Za Alloys Processed Through Centrifugal Casting” International Journal of
Mechanical Engineering & Technology (IJMET), Volume 4, Issue 1, 2013, pp. 163 - 172, ISSN
Print: 0976 – 6340, ISSN Online: 0976 – 6359.
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Cavitation In Centrifugal Pump” International Journal of Mechanical Engineering & Technology
(IJMET), Volume 4, Issue 3, 2013, pp. 359 - 366, ISSN Print: 0976 – 6340, ISSN Online: 0976 –
6359.

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