Back swept angle performance analysis of centrifugal compressor/Iscentrinio kompresoriaus menciu atlenkimo kampo tinkamumo analize.
Wang, Tie ; Peng, Cheng ; Wu, Jing 等
1. Introduction
With the development of automotive turbocharger, high efficiency,
high pressure ratio and wide operating range are required by centrifugal
compressor [1-3]. The compressor performances are important in
turbocharging field because they determine the engine air supply. The
most important component of centrifugal compressor is impeller [4].
Radial impeller has a wide application in diesel engine turbochargers
[5]. With the development of impeller, more and more gasoline engines
have installed turbochargers and the engine speed has been reaching more
than 5000 rpm. In order to adjust the very wide range of engine speed,
the selection of back swept angle has become the most important factor
for impeller design.
Liam Barr and Stephen Spence [6] established radial impeller with
25[degrees] back swept angel, after the comparing the numerical analysis
of 25[degrees] back swept blade with radial blade, it was concluded that
25[degrees] back swept blade offers significant increases of efficiency
while operated at lower velocity ratios. The similar conclusion was
drawn by Peng Sen and Yang Ce based on three-dimension Navier-Stokes
equations about 30[degrees] and 45[degrees] angle impeller of a
centrifugal compressor [7], it was concluded that an appropriate angle
can increase the range of a centrifugal compressor, improve the flow and
enhance the isentropic efficiency. Hildebrandt and Genrup [8] gave a
numerical investigation about the effect of different back swept
impeller of a centrifugal compressor, result shows that the back swept
angle provides a uniform flow pattern in term of velocity. The authors
found that an appropriate angle will be beneficial to performance of
centrifugal compressor. This paper adopts TurboSystem (a set of software
applications and software features for designing turbomachinery in the
ANSYS Workbench environment) to create the impeller flow field which is
impellers with 0[degrees], 2.5[degrees], 5[degrees], 7.5[degrees],
10[degrees], 12.5[degrees], 15[degrees] and 17.5[degrees] back swept
angles, and adopts CFX (a general purpose Computational Fluid Dynamics
software) to simulate every impeller, compares and analyzes the results
of flow field on different back swept angles through considering
pressure ratio, isentropic efficiency, volume flow rate and Mach number.
2. Three-dimensional finite element model of impeller
The TurboSystem consists of Vista CCD, BladeGen and TurboGrid
[9-11]. Vista CCD is integrated into ANSYS Workbench so that it may be
used to generate an optimized 1D (one-dimension) compressor design
before moved rapidly to a full 3D (three-dimension) model and CFD
(Computational Fluid Dynamics) analysis. In Vista CCD dialog box, the
input data can be specified on the Duty, Aerodynamic Data and Geometry
[12]. The data is shown in Table 1; impellers with 0[degrees],
2.5[degrees], 5[degrees], 7.5[degrees], 10[degrees], 12.5[degrees],
15[degrees] and 17.5[degrees] back swept angles are obtained by changing
the impeller outlet angle.
After establishing the 1D model of impeller, we continue to create
3D model of impeller. BladeGen is a geometry creation tool for turbo
machinery blade rows and we use it to create the 3D model of centrifugal
compressor impeller. After creating model of impeller, we continue to
generate the mesh of impeller. The geometry is exported through
TurboGrid which is a powerful blade mesh tool. These meshes are used in
the workflow to solve complex rotating blade passage problems. In order
to save simulation's time, we use single leaf channel flow field
[13], the high-quality hexahedral meshes of impeller view is shown in
Fig. 1 and the single leaf channel of impellers is shown in Fig. 2.
[FIGURE 1 OMITTED]
[FIGURE 2 OMITTED]
3 Simulation detail
The three dimensional numerical simulations to the air compressor
are carried out by CFX [14], which adopts a finite element based finite
volume to solve the Navier-Stoker equations for a structured grid. The
parameters of CFX basic setting are shown in Table 2. The boundary
condition consists of Inlet Temperature, Inlet Pressure, Mass Flow Rate
and Compressor Speed; the parameters of boundary condition are shown in
Table 3.
4. Effects of back swept angle impeller
4.1. Performance analysis of compressor impeller
Numerical simulation of compressor impeller pressure ratio with
different back swept angles (0[degrees], 2.5[degrees], 5[degrees],
7.5[degrees], 10[degrees], 12.5[degrees], 15[degrees], 17.5[degrees])
can be gotten and the 0[degrees] back swept impeller is radial impeller
[15].
Fig. 3 details the variation of pressure ratio of different back
swept angles. From 500 rpm to 1500 rpm, all the curves of pressure ratio
are increasing with engine speed; from 1500 rpm to 2500 rpm, all the
curves of pres sure ratio are decreasing with engine speed; more than
2500 rpm, all the curves of pressure ratio are increasing with engine
speed. Back swept impellers deliver decrease in pressure ratio while
operated from 500 rpm to 4500 rpm when compared to the radial impeller.
Fig. 4 details the variation of isentropic efficiency of different
back swept angles. From 500 rpm to 1000 rpm, all the curves of
isentropic efficiency are increasing with engine speed; from 1000 rpm to
3000 rpm, all the curves of isentropic efficiency are decreasing with
engine speed; more than 3000 rpm, all the curves of isentropic
efficiency are decreasing with engine speed. At 1000 rpm of the engine
speed, the isentropic efficiency of 15[degrees] back swept impeller is
more efficient than the other impellers (more than the radial impeller
0.78%); at 2000 rpm of the engine speed, the isentropic efficiency of
2.5[degrees] back swept impeller is more efficient than the other
impellers (more than the radial impeller 2.96%).
[FIGURE 3 OMITTED]
[FIGURE 4 OMITTED]
The parameters of volume flow rate and engine speed for 0[degrees],
5[degrees], 10[degrees] and 15[degrees] back swept angles are shown in
Table 4.
[FIGURE 5 OMITTED]
From 500 rpm to 1500 rpm, the back swept angle impellers deliver an
increase in volume flow rate when compared to the radial impeller.
4.2. Comparison and analysis of flow field
Compressible flows u can be characterized by the value of the Mach
number M [16]:
M [equivalent to] u/c, (1)
where c is the speed of sound in the gas.
When the Mach number is less than 1.0, the flow speed is called as
subsonic. At Mach numbers much less than 1.0, compressibility effects
are negligible and the pressure variation caused by gas density can
safely be ignored in flow modeling. When the Mach number approaches 1.0,
compressibility effects become important. When the Mach number exceeds
1.0, the flow speed is called as supersonic. The shock wave is one of
several different ways that supersonic flow gas can be compressed.
To each back swept angle, results are considered from the boundary
condition of 3500 rpm engine speed. Fig. 5 shows contour of Mach number
at different back swept angles. In Fig. 5, [theta] (radian) is used as
ordinate, and M (meter) is used as abscissa.
The shock wave is formed when fluid speed change faster than sound
speed [17]. The result shows that shock waves are formed on splitter
blade root when the back swept angle is increased. With the increasing
of back swept angle, the scope of shock wave is widened. Shock wave
significantly decreases the velocity at blade outlet. Shock wave can
cause a loss of total pressure.
5. Conclusions
The present study was undertaken to analyze the performance of
centrifugal compressor by using TurboSystem and CFX. We have simulated
the flow about compressor impeller at different back swept angles, there
are five conclusions:
1. Compared to the radial impeller, the back swept angle impellers
deliver decrease in pressure ratio, that is to say, back swept impellers
don't amplify pressure ratio of centrifugal compressor.
2. Compared to the efficiency of radial impeller, the back swept
impellers offer an increase in isentropic efficiency while operated from
1000 rpm to 2000 rpm. Draw a conclusion, that is, back swept angle
impeller can improve the centrifugal compressor isentropic efficiency
less than 2000 rpm engine speed.
3. Compared to the radial impeller, the back swept angle impellers
deliver increase about volume flow rate while operated less than 1500
rpm engine speed.
4. At 3500 rpm engine speed, shock waves are formed on splitter
blade root when the back swept angle is increased. The total pressure of
compressor is influenced by the shock wave. Shock wave can cause a loss
of total pressure.
5. As shown in Table 4 and Fig. 5, we find an appropriate back
swept angle can improve the volume flow rate of blade and enhance the
outlet velocity of compressor.
http://dx.doi.org/ 10.5755/j01.mech.20.4.4615
Received June 19, 2013
Accepted June 18, 2014
References
[1.] Nili-Ahmadabadi, M.; Poursadegh, F. 2013. Centrifugal
compressor shape modification using a proposed inverse design method,
Journal of Mechanical Science and Technology 27(3): 713-720.
http://dx.doi.org/10.1007/s12206-013-0120-0.
[2.] Korakianitis, T.; Hamakhan, I.A.; Rezaienia, M.A. 2012. Design
of high-efficiency turbomachinery blades for energy conversion devices
with the three-dimensional prescribed surface curvature distribution
blade design (CIRCLE) method, Applied Energy 89(1): 215-227.
http://dx.doi.org/10.1016/j.apenergy.2011.07.004.
[3.] Marsan, A.; Trebinjac, I.; Coste, S. 2013. Temporal behaviour
of a corner separation in a radial vaned diffuser of a centrifugal
compressor operating near surge, Journal of Thermal Science 22(6):
555-564. http://dx.doi.org/10.1007/s11630-013-0662-6.
[4.] Heinze, K.; Schrape, S.; Voigt, M. 2012. Probabilistic
endurance level analyses of compressor blade, CEAS Aeronautical Journal
3(1): 55-65. http://dx.doi.org/10.1007/s13272-012-0043-y.
[5.] Oyelami, A.T.; Adejuyigbe, S.B.; Waheed, M.A. 2012. Analysis
of radial-flow impellers of different configurations, The Pacific
Journal of Science and Technology 13(1): 24-33.
[6.] Liam, B.; Stephen, S.; Paul, E. 2009. Design and Analysis of a
Radial Turbine with Back Swept Blading, Fluid Machinery and Fluid
Mechanics, 115-121. http://dx.doi.org/10.1007/978-3-540-89749-1_15.
[7.] Peng, S.; Yang, C.; Ma, C.C.; Wang, H. 2005. Influence of
front lean angle on centrifugal compressor performance, Journal of
Tsinghua University (Science and Technology) 45(2): 250-253.
[8.] Hildebrandt, A.; Genrup, M. 2007. Numerical investigation of
the effect of different back sweep angle and exducer width on the
impeller outlet flow pattern of a centrifugal compressor with vaneless
diffuser, Journal of turbomachinery 129(2): 421-433.
http://dx.doi.org/10.1115/L2447873.
[9.] Wang, Y.; Luo, Z. 2011. Computational investigation on
centrifugal compressor performance at various altitudes, Advanced
Materials Research 230: 1123-1128.
http://dx.doi.org/10.4028/www.scientific.net/AMR.230 -232.1123.
[10.] Obrovsky, J.; Krausova, H. 2013. Development of high specific
speed Francis turbine for low head Hpp, Engineering Mechanics 20(2):
139-148.
[11.] Benini, E.; Biollo, R.; Ponza, R. 2011. Efficiency
enhancement in transonic compressor rotor blades using synthetic jets: A
numerical investigation, Applied Energy 88(3): 953-962.
http://dx.doi.org/10.1016/j.apenergy.2010.08.006.
[12.] Chen, S.; Yang, C.; Yang, C.M. 2012. Investigation of
geometrical parameters influence to the stress and aerodynamic
performance of centrifugal impeller, Fluid Machinery 40(3): 21-26.
[13.] Luo, Q.G.; Si, D.Y.; Ran, Z.G. 2013. Modal characteristics of
compressor blades considering fluid-solid interaction, Applied Mechanics
and Materials 37(6): 407-410.
http://dx.doi.org/10.4028/www.scientific.net/AMM.376 .407.
[14.] Dong, S.J.; Qi, B.; Wang, J. 2013. Optimization of loss
models for centrifugal compressor performance prediction based on
numerical analysis results, Applied Mechanics and Materials 300:
225-231. http://dx.doi.org/10.4028/www.scientific.net/AMM.300 -301.225.
[15.] Chunxi, L.; Ling, W.S.; Yakui, J. 2011. The performance of a
centrifugal fan with enlarged impeller, Energy Conversion and Management
52(8): 2902-2910. http://dx.doi.org/10.1016/j.enconman.2011.02.026.
[16.] Muhammad, N.L.; Seong, S.K. 2012. Numerical investigation of
the effect of inlet skew angle on the performance of mechanical vapor
compressor, Desalination 284: 66-76.
http://dx.doi.org/10.1016/j.desal.2011.08.038.
[17.] Settles, Gary S. 2006. High-speed Imaging of Shock Wave,
Explosions and Gunshots, American Scientist 94(1): 22-31.
http://dx.doi.org/10.1511/2006.57.986.
Tie Wang, Cheng Peng, Jing Wu
School of Vehicle and Traffic, Shenyang Ligong University, Shenyang
110159, China, E-mail: wangtielucky@126.com
Table 1
The Vista CCD input data
Parameters Value
Pressure ratio 1.8
Mass flow, kg/s 0.106
Rotational speed, rev/min 66322
Hub diameter, mm 5
Shroud diameter, mm 60
Rake angle, [degrees] 30
Vane inlet angle, [degrees] 60
Back swept angle, [degrees] 0, 2.5, 5, 7.5, 10, 12.5, 15, 17.5
Number of main blade 9
Number of splitter blade 9
Table 2
The parameters of CFX basic setting
Parameter settings Value
Fluid region Turbo mode
Machine type Centrifugal compressor
Rotating axis Z
Analysis type Steady state
Turbulence model k-Epsilon
Table 3
Data of centrifugal compressor in different engine speed conditions
Engine speed, Mass flow, Compressor Inlet Inlet
rpm kg/s speed, rpm temperature, pressure,
K Bar
500 0.00893 39023 299.65 0.999
1000 0.0193 43820 299.43 0.998
1500 0.0320 48544 299.19 0.997
2000 0.0460 52503 298.97 0.995
2500 0.0645 57367 298.67 0.991
3000 0.0822 61434 298.44 0.987
3500 0.106 66322 297.93 0.978
4000 0.139 72767 297.18 0.966
4500 0.185 79977 296.08 0.947
Table 4
Parameters of volume flow rate and engine speed with
different back swept angles
Volume Flow Rate, [m.sup.3]/s
Engine
Speed, rpm 0[degrees] 5[degrees] 10[degrees] 15[degrees]
500 0.0417 0.0418 0.0420 0.0421
1000 0.0936 0.0945 0.0953 0.0960
1500 0.1509 0.1518 0.1528 0.1534
2000 0.1916 0.1901 0.1916 0.1913
2500 0.2031 0.2018 0.2002 0.1982
3000 0.2055 0.2038 0.2020 0.2000
3500 0.2077 0.2059 0.2040 0.2020
4000 0.2098 0.2085 0.2067 0.2046
4500 0.2134 0.2116 0.2098 0.2078
