Computational Analysis of a Centrifugal Compressor with Partial … · A low speed centrifugal...

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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.



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



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



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.



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.



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


Fig. 8. (c) Total pressure contours at meridional plane surface at 1.8 with and without partial shroud at 2.2% tip clearance for


SS

SS

SS

SS

SS

SS

PS PS

PS PS

PS

PS



Fig. 8. (d) Total pressure contours at meridional plane surface at 1.8 with and without partial shroud at 5.1% tip clearance for


Fig. 8. (e) Total pressure contours at meridional plane surface at 1.8 with and without partial shroud at 5.1% tip clearance for


Fig. 8. (f) Total pressure contours at meridional plane surface at 1.8 with and without partial shroud at 5.1% tip clearance for


SS

SS

SS

SS

SS SS PS

PS

PS PS

PS

PS



Fig. 8. (g) Total pressure contours at meridional plane surface at 1.8 with and without partial shroud at 7.9% tip clearance for


Fig. 8. (h) Total pressure contours at meridional plane surface at 1.8 with and without partial shroud at 7.9% tip clearance for


Fig. 8. (l) Total pressure contours at meridional plane surface at 1.8 with and without partial shroud at 7.9% tip clearance for


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



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


-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


5.1%_With_PS_0.215


7.9%_With_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


5.1%_With_PS_0.285


7.9%_With_PS_0.285




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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