Flow Analysis of Centrifugal Compressor Impeller for a ...199.62mm), the blade tip (d 2 ... (also...

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ISSN 2319-8885

Vol.03,Issue.25

September-2014,

Pages:5069-5075

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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



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.




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.




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.




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




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.

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