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ISSN 2319-8885
Vol.03,Issue.25
September-2014,
Pages:5069-5075
Copyright @ 2014 SEMAR GROUPS TECHNICAL SOCIETY. All rights reserved.
Flow Analysis of Centrifugal Compressor Impeller for a Turbocharger AUNG AUNG
1, WIN PA PA MYO
2, ZAW MOE HTET
3
Dept of Mechanical Engineering, Mandalay Technological University, Mandalay, Myanmar.
Abstract: This paper presents the flow analysis of centrifugal compressor impeller for a turbocharger. The impeller is designed
by assuming 575kW power supplied by the turbine (allowing for bearing friction) at 19500 rpm and 20 twisted blades. In so
doing, the diameters of the hub (dh1=73.98mm), the shroud at inlet (ds1=199.62mm), the blade tip (d2=391.2mm), the blade
angles at hub (βbh1 =59.31 degree), at shroud inlet (βbs1=31.98 degree), at impeller outlet (βb2=72.75 degree) are calculated. The
geometry of this impeller and fluid domain around one blade can be achieved by using CFturbo 9.1 with these design data. The
flow analysis of the compressor can be reached by importing fluid domain in the CFX from ANSYS 12.0 to show the
comparison of pressure and temperature distribution across the impeller by theoretical and ANSYS simulation results.
Keywords: Turbocharger; Turbine; Compressor; CFturbo; ANSYS.
I. INTRODUCTION
A turbocharger consists of a turbine and a compressor
connected by a shaft. The turbine section is mounted to the
exhaust line from the engine. The compressor is connected
to the turbine by a shaft and its outlet is routed to the engine
air intake. Exhaust gas from the engine enters the turbine
and expands, performing work on the turbine. The turbine
spins the shaft connected to the compressor. The compressor
draws in ambient air and compresses it. Turbocharger
systems are measured by the amount of pressure the
compressor can output above ambient. This pressure is
commonly called boost pressure or boost. Therefore, the
compressor is also the main part of the turbocharger to arise
pressure for diesel engine. A centrifugal compressor
consists of three major sections with regard to the path
through which the fluid passes. These are the inlet to the
impeller (also known as the eye of the impeller or inducer
section), the impeller section and the diffuser section.
The inlet section may consist of suction elbow and guide
vanes. The guide vanes give the fluid some degree of pre-
whirl or pre-rotation before entering the impeller section. In
the absence of guide vanes, the fluid flows axially into the
impeller section. A compressor stage is made up of the
impeller and diffuser sections. What goes on inside the
centrifugal compressor is very much influenced by the
conditions of the fluid flow at the inlet of the compressor.
Thus obtaining optimal flow of the working fluid through
the compressor stage requires proper design of the
compressor inlet and appropriate determination of the flow
conditions at the inlet. The design of compressor has
developed with the power supplied by the turbine(allowing
for bearing friction), P,575 kW, air mass flow , m, 4 kg/s,
rotational speed, N, 19500 rpm, and the number of impeller
blade, Z, 20. In this paper, the impeller of compressor is
designed with CFturbo9.1 software and 3-D simulation
study of the impeller can be achieved by helping of CFD
software ANSYS CFX.
II. DESIGN OF IMPELLER WITH CFTURBO9.1
Compressor design is complex and time consuming.
Therefore modern high-quality software tools are required to
enable the engineer to create and analyze several geometry
variations and find quickly an optimal solution. Here, the
application of CFturbo9.1 is now used to design the
impeller. To get this geometry, five parameters should be
given:
Fluid properties as ideal gas or as real gas with
compressibility factor.
Best point: mass flow, speed, specific work.
Inlet condition: pressure and temperature.
The main dimensions of hub and suction diameters as
well as outlet width and diameter.
The size of the tip, direction of rotation and blade
numbers as well as spliter blade.
The design data can be transformed into a parametric CAD-
modal and other neutral format such as STEP or IGES. The
design procedure is shown in figs.1, 2 and 3.
II. FLOW ANALYSIS OF THE IMPELLER
The geometry of the fluid domain [Fig.5] imports to
ANSYS CFX workbench. After creating the model, meshing
is also done in CFX itself. This meshing domain is repeated
twelve times at Turbo mode in CFX because the impeller
has 12 blades. The whole domain of the impeller is meshed
AUNG AUNG, WIN PA PA MYO, ZAW MOE HTET
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.25, September-2014, Pages: 5069-5075
by using the unstructured type of grid is as shown in Fig.4.
Triangles in 2D and tetrahedral in 3D typically utilize in
unstructured grids. Unstructured grid method gives the
advantage that they are much automated and, therefore,
Fig.1. Initial data input in the CFturbo9.1 software.
Fig.2. Main dimensions input the CFturbo9.1.
Fig.3. Meridional contour.
require little user time or effort. The details of meshing of
completed domain are shown in table1. ANSYS CFX solves
the fully 3D, compressible, viscous, turbulent analysis of the
fluid (air) flow. The total pressure and total temperature
always set at the inlet boundary conditions. At the outlet
static pressure boundary conditions for higher mass flow are
set, for lower mass flow, the mass flow boundary conditions
are set. The speed of impeller [rev/min] is also set.
Fig.4. The geometry of impeller.
Fig.5. The geometry of fluid domain.
TABLE I: Results of Impeller
Flow Analysis of Centrifugal Compressor Impeller for a Turbocharger
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.25, September-2014, Pages: 5069-5075
III. BOUNDARY CONDITIONS
At the inlet, the boundary is defined as subsonic inlet,
with measured total temperature, total pressure and flow
direction profiles. The turbulence level is defined to be
median intensity of about 5% because there is no idea of the
turbulence levels in this simulation. The blade, hub and
shroud are defined as adiabatic walls with appropriate
rotational velocity and no-slip. At the outlet boundary
conditions static pressure is set. The geometry [Fig.6] and
mesh [fig.7], by using the unstructured type of grid in table
(2) of the domain can be achieved. The following data in
table (3) input the CFX and the boundary conditions are also
set [table (4) and table (5)]. Fig.8 provides the summary of
the boundary conditions used in the impeller.
TABLE II: Meshing Details of Fluid Domain
Fig.6. The Geometry of Domain by Importing
ANSYS12.0.
Fig.7. The mesh of fluid domain.
Fig.8. Boundary conditions used in the impeller
simulation.
Fig.9. Isometric 3D View of the Blade, Hub and Shroud.
Fig.10. Meridional View of the Blade, Hub and Shroud.
AUNG AUNG, WIN PA PA MYO, ZAW MOE HTET
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.25, September-2014, Pages: 5069-5075
Fig.11. Static pressure Distribution across the Impeller.
Fig.12. Total pressure Distribution across the Impeller.
Fig.13. Static Temperature Distribution across the
Impeller.
Fig.14. Total Temperature Distribution across the
Impeller.
Fig.15. Static Pressure Distribution across the Blade to
Blade.
Fig.16. Total Pressure Distribution across the Blade to
Blade.
Flow Analysis of Centrifugal Compressor Impeller for a Turbocharger
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.25, September-2014, Pages: 5069-5075
Fig.17. Temperature Distribution across the Blade to
Blade.
Fig.18. Total Temperature Distribution across the Blade
to Blade.
Fig.19. Mach Number Distribution across the Blade to
Blade.
Fig.20. Absolute Velocity Distribution across the Blade
to Blade.
Fig.21. Chart of Streamwise Location and Pressure on
Inlet to Outlet.
Fig.22.Chart of Streamwise Location and Total Pressure
on Inlet to Outlet.
AUNG AUNG, WIN PA PA MYO, ZAW MOE HTET
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.25, September-2014, Pages: 5069-5075
Fig.23. Chart of Streamwise Location and Temperature
on Inlet to Outlet.
Fig.24. Chart of Streamwise Location and Total
Temperature on Inlet to Outlet.
Fig.25. Chart of Streamwise Location and Absolute
Velocity on Inlet to Outlet.
Fig.26. Chart of Streamwise Location and Mach
Number on Inlet to Outlet.
TABLE III: Domain Physics for CFX
TABLE IV: Boundary Conditions of Impeller Inlet &
Outlet
TABLE IV: Boundary Conditions of Impeller Blade,
Hub and Shroud
Flow Analysis of Centrifugal Compressor Impeller for a Turbocharger
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.25, September-2014, Pages: 5069-5075
IV. THE RESULTS OF FLUID FLOW
From fig.11 to 14, show the static pressure, total pressure,
static temperature and total temperature distributions across
the impeller. From fig.15 to 20, describe the static and total
pressures, the static and total temperatures, Mach Number
and absolute velocity distribution across the blade to blade.
The chart figures [Figs.21 to 26] are achieved by
transferring data from ANSYS to MATLAB. In this charts,
the streamwise locations are divided into 5 parts on the inlet
to outlet meridional views. In the first chart, the static
pressure is nearly constant by 88.189 kPa over 0.2 on
streamwise location. From this point, there is a gradual
incline in the 103 kPa of pressure over 0.4 of streamwise
location. The pressure is constant 103 kPa between 0.4 and
0.6. And, then, there is a dramatic rise in the 200 kPa of the
pressure at outlet. At the second, total pressure (100 kPa) is
constant over 0.2 on the streamwise location. From this
point, the total pressure is gradually increased to 359.877
kPa on the end of the streamwise location. On the third, the
static temperature is slightly constant at 284.541 K over 0.2.
From this point, the temperature is gradually inclined to 298
K beyond 0.4 of streamwise location. The temperature
maintains at 298 K between 0.4 and 0.6. And, then, there is
a dramatic rise in the 362.853 K of the temperature on 1.0
streamwise location. In the fourth, the total temperature is
constant at 293 K over 0.2. From this point, there is a
gradual increase in the total temperature (428.454 K) on the
end of streamwise location.
TABLE VI: Comparison of Theoretical and ANSYS
Results at Inlet
TABLE VII: Comparison of Theoretical and ANSYS
Results at Outlet
On the fifth, the absolute velocity is nearly constant by
130.41 m/s over 0.2 on the streamwise location. From this
point, the velocity is dramatically increased to 280 m/s over
0.6. And, then, there is a gradual incline in the velocity
(362.468 m/s) at the outlet. On the sixth, the Mach number
maintains at 0.385583 over 0.2 of the streamwise location.
From this point, there is a dramatic incline in the Mach
number (about 0.8) over 0.6. And, then, it is gradually
increased to 0.948881 on the end of streamwise location.
Here, the comparison of theoretical and ANSYS simulation
results are shown in Tables (6) and (7).
V. CONCLUSIONS AND RECOMMENDATIONS
The modal for the impeller of centrifugal compressor has
been developed by using CFturbo9.1 software. The analysis
has been carried out with the help of ANSYS12.0. In this
paper, the fluid flow domain of the impeller is analysed. The
next suggestion is to be analysed the fluid flow of the whole
centrifugal compressor. The job of a diesel engine
turbocharger is to supply compressed air to the engine for
increasing power output. Turbine drives the centrifugal
compressor with the engine exhaust gas power. This
impeller is designed by the power from the turbine. The
vanned diffuser and volute are recommended to design on
which the design of impeller depends.
VI. ACKNOWLEDGMENT
The author likes to acknowledge the supports provided by
Dr. Win Pa Pa Myo, thesis supervisor of the author, and U
Zaw Moe Htet, co-supervisor of thesis. The author is also
thankful to Dr. Ei Ei Htwe, Head of mechanical engineering
department, Mandalay Technological University, for her
valuable guidance.
VII. REFERENCES
[1] S. L. Dixon, B. Eng., Ph.D. Honorary Senior Fellow,
Department of Engineering, University of Liverpool, UK
and C. A. Hall, Ph.D. University Lecturer in
Turbomachinery, University of Cambridge, UK: Fluid
Mechanics and Thermodynamics of Turbomachinery .
[2] H. Tamaki and S. Yamaguchi : The Experimental Study
of Matching Between Centrifugal Compressor Impellers and
Vaneless Diffuser for Turbochargers Proceedings of ASME
TURBO EXPO 2007 GT2007- 28300 (2007).
[3] G. Kreuzfeld and R. P. Müller, “An Advantageous Tur-
bomachinery Design Method,” Compressor Tech Two,
August-September 2011.
[4] Cumpsty, N. A. (1989). Compressor Aerodynamics,
London: Longman.
[5] Watson, N., and Janota, M. S. (1982). Turbocharging the
Internal Combustion Engine.
[6] Khin Maung Aye, U: Fluid Machinery for Mechanical
Engineers, December, 2000.
[7] Church, Austin H.: Centrifugal Pumps and Blowers,
John Wiley and Sons, Inc. Chapman and Hall, Ltd., New
York, 1972.
[8] Victor L . Streeter, Professor Emeritus of Hydraulics,
University of Michigan: FLUID MECHANICS, Seventh
Edition.