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Volume-7, Issue-3, May-June 2017
International Journal of Engineering and Management Research
Page Number: 242-251
Computational Analysis of a Centrifugal Compressor with Partial Shroud
on Tip of the Blade
S. M. Swamy
1, V. Pandurangadu
2, V. Naga Prasad Naidu
3, R. Rama Chandra
4 1Assistant Professor, G. Narayanamma Institute of Technology and Sciences, Shaikpet, Hyderabad, INDIA
2Professor, J. N. T. U.A, College of Engineering Anantapur, A. P, INDIA
3Professor & Principal, Department of Mechanical Engineering Intell Engineering College, Anantapur, A.P, INDIA
4Professor & Principal, Department of Mechanical Engineering SKD Engineering College, Gooty, A.P, INDIA
ABSTRACT Computational analyses of flow field in a centrifugal
compressor with partial shroud on tip of the blade are
presented in this paper. A low speed centrifugal compressor
with three tip clearances i.e.,τ = 2.2%, 5.1% and 7.9% of
blade height at trailing edge are examined at four flow
coefficients φ = 0.12, 0.18,0.28 and 0.34. Analysis is carried
out for two different cases, one without partial shroud on the
tip of the blade and second with partial shroud on the tip of
the blade. The two cases are studied at four different flow
coefficients using ANSYS - CFX. Pressure ratio improvement
with partial shroud on tip of the blade is observed. The
leakage of flow over tip of the blade through the partial
shroud from pressure side to suction side of the blade is
interacting with passage wake near shroud and reduction in
passage wake region area is observed with partial shroud on
tip of the blade. Increase in the velocity of the fluid in passage
wake is also observed with partial shroud on tip of the blade.
For partial shroud on tip of the blade also, increase of
velocity in passage wake is observed but reduction in
pressure ratio is observed due to more leakage flow.
Keywords-- Centrifugal Compressor, Flow coefficient,
partial shroud on tip of the blade, passage wake.
I. INTRODUCTION
In turbo-machines, to desensitize tip gap impacts,
squealer tips/partial shroud, tip geometry alterations,
shroud treatment and so forth are proposed in the
literature. P. Usha Sri and N. Sitaram observed that the
impeller with the chamfer on suction surface of the blade
tip demonstrates shows small improvement in
performance. With an increase in the chamfer
measurement on suction surface of blade tip, performance
change is observed. Through experimental analyses, S.
Senthil and N. Sitaram concentrated the performance of a
centrifugal compressor by means of squealer tips. They
analysed increment in energy coefficient and efficiency
with squealer tips on pressure surface side. S. Senthil and
N. Krishna Mohan found that slanting sort squeeler tip has
advantageous impacts. Chi-Young Park et. al have
observed change of performance and surge margin with
ring groove framework on centrifugal compressor. Fayez
M. Wassef et. al have directed investigations on
centrifugal compressor and observed change in limit of
stability with addition of a ring and a groove in the shroud
in diffuser region..
II. 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= 53o
Blade angle at inducer tip, β1t = 35o 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.
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Centrifugal impeller with above specifications
with 3 mm thickness throughout the blade, 2.2% 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 15.0 software is used for
obtaining the solution and standard k-ε turbulence model is
used for the closure. The centrifugal compressor is
analysed at four different flow coefficients (0.12, 0.18,
0.28 and 0.34).
Fig. 1. Centrifugal compressor (without and with PS)
Fig. 2. Computational domain of single passage (without and with PS)
Fig. 3. Blade geometry without and with partial shroud
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Fig. 4. Three dimensional mesh for single blade row without and with partial shroud.
Partial shroud attached on tip of the blade of the
impeller, the partial shrouds are made of stainless steel of
0.1 mm thickness. The stainless steel sheet is cut to the
shape of rectangle pieces of 50 mm x 5 mm size. These
rectangle pieces are attached to the tip of the blades using
araldite. The configurations tested (basic configuration
without partial shroud and configuration with partial
shroud) are shown in Fig. 2. The blade-to-blade view
showing the partial shroud on the rotor tip is also shown in
Fig. 3.
Fig. 3 Blade-to-blade view of the impeller without and with partial shroud on rotor blade tip
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III. RESULTS AND DISCUSSIONS
Velocity Streamlines The velocity streamline give an insight into the
impeller flow behavior and velocity on casing in without
and with partial shroud are shown in figure 4 (a) and (b).
When the vanes of diffuser are nearer to the impeller the
opposite flow enhances the tip leakage flow near the
impeller exit. This can be clearly seen from the streamlines
pattern. The separated flow from the diffuser vane does not
influence the impeller exit flow when there is sufficient
radial gap. Hence the losses at the impeller exit are also
smaller.
Fig. 4. (a) Velocity on casing for without and with partial shroud at 2.2% tip clearance for 0.12 flow coefficient
Fig. 4.(b) Velocity stream line plot for without and with partial shroud at 2.2% tip clearance for 0.34 flow coefficient.
IV. STATIC PRESSURE CONTOURS AT
SPAN 0.7
Static pressure contours view in blade to blade, at
span 0.7 is shown in figures 5-7. The contours show
gradual pressure increases from inlet to exit of the impeller
due to action of the dynamic rotating impeller. With partial
shroud on tip of the blade, maximum pressure change is
observed. But without partial shroud on tip of the blade,
the pressure at outlet is reduced.
Fig. 5. Static pressure contours for 2.2% tip clearance without PS and with PS at span 0.7 at mass flow rate 0.087kg/sec.
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Fig. 6. Static pressure contours for 2.2% tip clearance without PS and with PS at span 0.7 at mass flow rate 0.14kg/sec.
Fig. 7. Static pressure contours for 2.2% tip clearance without and with partial shroud at span 0.7 at mass flow rate 0.215kg/sec
V. TOTAL PRESSURE CONTOURS ON
MERIDIONAL PLANE AT TURBO
SURFACE 1.8
Total pressure contours on meridional plane for
two configurations with and without partial shroud for
three tip clearances 2.2%, 5.1% and 7.9% are appeared in
figures 8. (a), (b), (c), (d), (e), (f), (g), (h), (i), (j), (k) and
(l). Fluid flow for basic configuration at tip of the blade on
suction side close tip region high total pressure area of
passage wake is observed. With partial shroud on tip of the
blade, low total pressure area of section wake is decreased.
The leakage flow out of the pressure side is associating
with entry wake. With partial shroud on tip of the blade for
2.2% of clearance, total pressure is higher at pressure
surface side due to the rotation and meridional curvature
and low total pressure is observed near the suction surface
side because of the boundary layer on stationary casing.
For other tip clearances the wake area is analysed. When
contrasted with low tip clearance at other tip clearances,
because of leakage flows, total pressure on suction side is
additionally decreased and the total pressure on pressure
side is also reduced. The wake section region is expanding
with increment in tip clearance. At 7.9% tip clearance the
low total pressure area is noteworthy and furthermore the
position is far from the suction side shroud corner. With
the tip clearance increase, the total pressure on pressure
side is diminished as mass flow rate of leakage fluid from
tip gap increases. The expansion in wake area and
movement of wake along shroud towards pressure surface
is analysed. The total pressure coefficient at suction side of
hub corner is expanded, due to secondary flow, which
makes the fluid move vertically up. Total pressure gradient
close to the blade end which cause stream and wake flow
at trailing edge is additionally observed. Comparable
patterns are observed for all flow coefficients.
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Fig. 8. (a) Total pressure contours at meridional plane surface at 1.8 with and without partial shroud at 2.2% tip clearance for
flow coefficient 0.18.
Fig. 8 (b) Total pressure contours at meridional plane surface at 1.8 with and without partial shroud at 2.2% tip clearance for
flow coefficient 0.28.
Fig. 8. (c) Total pressure contours at meridional plane surface at 1.8 with and without partial shroud at 2.2% tip clearance for
flow coefficient 0.34.
SS
SS
SS
SS
SS
SS
PS PS
PS PS
PS
PS
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Fig. 8. (d) Total pressure contours at meridional plane surface at 1.8 with and without partial shroud at 5.1% tip clearance for
flow coefficient 0.18.
Fig. 8. (e) Total pressure contours at meridional plane surface at 1.8 with and without partial shroud at 5.1% tip clearance for
flow coefficient 0.28.
Fig. 8. (f) Total pressure contours at meridional plane surface at 1.8 with and without partial shroud at 5.1% tip clearance for
flow coefficient 0.34.
SS
SS
SS
SS
SS SS PS
PS
PS PS
PS
PS
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Fig. 8. (g) Total pressure contours at meridional plane surface at 1.8 with and without partial shroud at 7.9% tip clearance for
flow coefficient 0.18.
Fig. 8. (h) Total pressure contours at meridional plane surface at 1.8 with and without partial shroud at 7.9% tip clearance for
flow coefficient 0.28.
Fig. 8. (l) Total pressure contours at meridional plane surface at 1.8 with and without partial shroud at 7.9% tip clearance for
flow coefficient 0.34.
VI. RADIAL VELOCITY DISTRIBUTION
Radial velocity appropriations from the hub to the
shroud at the impeller exit for three tip clearances and for
four flow coefficients at two configurations is appeared in
figure 9. (a), (b) and (c). It is observed that radial velocity
somewhat increases at flow coefficients = 0.34 and 0.28
in the impeller shroud area for the configuration with
partial shroud as compared to the basic configuration. It is
additionally observed that at the shroud region for three
values of flow coefficients demonstrate diminish in radial
velocity. At shroud region boundary layer thickness
increases due to partial shroud. Hence higher stacking on
the blade causes diminish in radial velocity. At the
impeller exit with partial shroud the flow close to the
shroud is secondary flow that block the flow passage. The
tip loss flow impacts the secondary flow structure and
further obstructs the flow entry, in this manner producing a
substantial total pressure loss near the shroud. The
blockage appears in a fast reduction in the radial velocity
close to the shroud in every one of the three tip clearances.
However at 2.2% of tip clearance no turn around flow was
seen close to the shroud, the blockage is smaller for this
situation than in the without partial shroud. For the tip
clearance 2.2% incorporated the low misfortune area close
to the shroud. The higher radial velocity close to the
shroud in 2.2% of tip clearance was the reduced tip
leakage flow in the tip region. The radial velocity
SS SS
SS
SS
SS SS
PS PS
PS
PS
PS PS
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dispersion is for 5.1% and 7.9% of tip clearances are
practically indistinguishable. This result suggested that the
radial velocity distribution in the span wise direction at the
impeller exit depended strongly on the tip clearance at the
trailing edge.
Fig. 9. (a) Radial velocity distribution from hub to shroud at impeller exit for flow coefficient 0.18.
Fig. 9. (b) Radial velocity distributions from hub to shroud at impeller exit for flow coefficient 0.28.
Fig. 9. (c) Radial velocity distributions from hub to shroud at impeller exit for flow coefficient 0.34.
VII. CONCLUSIONS
A low speed centrifugal compressor with three tip
clearances with two configurations without and with
-1
0
1
2
3
4
5
6
0 0.2 0.4 0.6 0.8 1
Rad
ial
Vel
oci
ty,
(m/s
)
Span Normalized Hub to Shroud
2.2%_With_PS
2.2%_Without_PS
5.1%_With_PS_0.14
5.1%_Without_PS_0.14
7.9%_With_PS_0.14
7.9%_Without_PS_0.14
-2
0
2
4
6
8
0 0.2 0.4 0.6 0.8 1 1.2
Rad
ial
Vel
oci
ty,
(m/s
)
Span Normalised Hub to Shroud
2.2%_With_PS_0.215
2.2%_Without_PS_0.215
5.1%_With_PS_0.215
5.1%_Without_PS_0.215
7.9%_With_PS_0.215
7.9%_Without_PS_0.215
-2
0
2
4
6
8
10
0 0.2 0.4 0.6 0.8 1 1.2
Rad
ail
Vel
oci
ty,
(m/s
)
Span Normalised Hub to Shroud
2.2%_With_PS_0.285
2.2%_Without_PS_0.285
5.1%_With_PS_0.285
5.1%_Without_PS_0.285
7.9%_With_PS_0.285
7.9%_Without_PS_0.285
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partial shroud on tip of the blade are analysed at four
different flow coefficients. The results are compared with
the without partial shroud on tip of the blade. Without
partial shroud on tip of the blade, though velocity at the
meridional section around the partial shroud is increased,
the pressure at outlet is reduced because of more leakage
of flow over the blades. With partial shroud on tip of the
blade, due to the interaction of the leakage flow from
partial shroud with passage wake, the total pressure
improvement is observed. Also with partial shroud on tip
of the blade, static pressure rise at outlet is observed for all
coefficients.
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] 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.
[7] 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.
[8] Shalin Marathe and Rishi Saxena, “Numerical Analysis
on Effect of Exit Blade Angle on 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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