CFD Analysis of the Turbocharger Compressor Housing In Different Mass Flow Rate

Zhou Weiru1*, Wang Yan1, Fan Junlei2

1.Changchun FAWER-IHI Turbo Co.,Ltd, ChangChun 130000, China 2. CD-adapco China, Beijing 100102, China *Corresponding Author: Tel:0431-81816771, Email:[email protected] connected by a common shaft. This kind of Abstract turbocharger has a common problem-turbocharger lag [3]. Analysis of Newton’s second law of motion In this work a CFD analysis of compressor flow for rotational systems suggests reducing the rotor field using STAR-CCM+ is made. First of all, the size and mass will reduce turbocharger lag [4-5]. boundary conditions and MRF region are defined Electrically assisted turbocharging systems used to simulate the performance of compressor electrical machines in motoring mode to impart housing. Then, compare the compressor housing additional power onto the common shaft during experimental data which were made by No.1 low load operation to improve upon the laboratory with the simulation data to verify the performance of the fixed geometry variant [6]. VG difference of them. Hence a numerical analysis has devices were employed different designs and were been carried out in this work to extensively explore employed in different ways to alter the cross compressor pressure ratio as well as to predict the sectional area of the housing or inlet which guides flow and turbulence characteristics of the the exhaust gas into the turbine rotor; these devices centrifugal compressor by varying the mass flow could also be coupled with diffusers to effect rate without changing the number of impeller variable geometry for the compressor [7-12]. blades and compressor speed. There are two However, because of complex geometry of the important mass flow rates points including surge turbocharger volute, it costs a lot of time and labor and choke points to simulate. It is found from the power to adopt experiment to gain relevant data of analysis that different mass flow rate presents a volute [13]. So it becomes more economical to considerable effect on the pressure and temperature simulate turbocharger internal flow field and at the compressor outlet. Furthermore, it also analysis data using the CFD software [14]. affects the air speed around the compressor wheel.

Keywords: compressor housing; CFD; pressure; temperature;

1 Introduction With the development of environmental protection in many countries, energy-saving missions have become the goal of engine industry. The turbocharger has an irreplaceable role in improving engine power, reducing fuel consumption and decreasing emissions [1]. A turbocharger, or colloquially turbo, is a turbine- Fig.1 Turbocharger components and operational drive forced induction device that increases an principle internal combustion engine’s efficiency and power output by forcing extra air into the combustion 2 CFD analysis of compressor housing chamber [2]. It’s operational principle is shown in Figure 1.This improvement over a naturally Based on an existing turbocharger product, the 3D aspirated engine's power output is due to the fact models of turbocharger compressor housing and that the compressor can force more air—and compressor wheel are established via CATIA proportionately more fuel—into the combustion software. Then, the compressor housing flow field chamber than atmospheric pressure. is extracted by the CFD software. And finally the There were numerous technology variants available tested 3D models will be imported into the STAR- on the commercial market, as well as under CCM+ for CFD simulation [15]. The existing development. The most basic technology was the turbocharger compressor housing product is shown conventional, fixed geometry turbocharger, which in Figure 2. consists of turbine and compressor wheels 2.2 The establishment of finite element model The compressor wheel is situated inside the compressor house, and encapsulated with a cover which generates the Multiple Reference Frame (MRF) region. The Multiple Reference Frame (MRF), also known as the frozen rotor, keeps the mesh stationary and simulates the movement by using a rotating coordinate system. The main advantage of the MRF approach is its low computational cost, at the expense of neglecting the blade passage effect and the stator-rotor interaction Fig.2. Turbocharger compressor housing [16]. Having imported the CAD model of the compressor into the CFD software, surface and 2.1 The establishment of compressor housing flow field volume meshes were generated. The polyhedral mesh was used as it can fit more easily with According to the actual compressor housing, complex geometry. Prism layers at the tip of the CATIA 3D model is established and at the same blades of the compressor wheel was used to time the compressor housing flow field is extracted. accurately predict the wall shear stresses. A mesh The model is shown in Figure 3. Moreover, a containing 1.68 million cells was used for the compressor wheel is established by the software simulations. Extrude mesh are used at inlet and which is shown in Figure 4. outlet which length are 100 mm. The mesh structure is shown in Figure 5.

2.3 Physics model Reynolds Averaged Navier-Stokes (RANS) equations are solved together with the energy equation. The coupled flow model was used to achieve stable and converged solution particularly at high flow velocities. In all simulations, the flow is assumed steady and ideal gas equation is employed to calculate the density. The simulation Fig.3. Compressor housing flow field model continues until there is no change in mass flow rate and residuals of the governing equations reaches at least 0.001. Post processing available in STAR CCM+ is used to analysis the spatial distribution of the flow velocity vectors, pressure and turbulence parameters.

Fig.4. Compressor wheel model

Fig.5 The meshed model 2.4 Boundary conditions and model parameter For the flow field simulations of the compressor housing, it is essential to define boundary conditions properly. In this study, inlet stagnation conditions and mass flow rate outlet condition were considered at the inlet and outlet consequently. Four operating points of different mass flow rates were simulated at the same impeller speed of 160000 rpm. The details of these parameters are shown in table 1. Tab. 1 Boundary conditions parameters Fig.7 boundary value Pres Inlet temperature 20 ℃ sure Inlet pressure 0 Pa distri Speed 160000 butio rpm n at 160000 rpm 3 CFD result 3.2 Temperature The compressor wheel speed is fixed at 160000 rpm. After 14000 iterations, the results are The spatial distribution of the temperature of the converged and believable. In this paper, the mass volute is shown in Figure 8. Maximum temperature flow rate of inlet is considered the most important on the compressor flow field was found to be parameter which is used to decide when stop the 392.29K. The temperature is increasing from inlet to outlet. calculation. For example, the outlet mass flow rate is -0.09983 kg/s, to decide when to stop the calculation, the inlet mass flow rate must reach - 0.09983 kg/s for thousands of iterations. The plot is shown in Figure 6.

Fig.8 Temperature distribution at 160000 rpm

Fig.6 Inlet mass flow rate monitor 3.3 Vector 3.1 Pressure The Figure 9 shows the velocity magnitude A contour plot of pressure at the compressor volute contours, because all the simulations presented in is given in Figure 7. The pressure distribution this paper are at the speed of 160000rpm, the through volute increase from inlet to outlet. During tangential velocities at the impeller exit are similar the simulation process, before 6000 iterations, the for all the simulations, and the radial velocity at the data fluctuate dramatically. After that, the pressure impeller exit is mainly dictated by the air flow. remain steady. The pressure distribution remain Maximum speed on the compressor wheel tip was constant along its length. found to be 361.21m/s. Maximum mach number on the MRF region was found to be 1.1382. But from the figure 10 we can see that the mach number distribution is at at the FIT Turbocharger Company No.1 laboratory, the lever of 0.68297 to 0.91059. shown in Figure 11. The facilities are used for identifying the performance of turbocharger compressors with mass flow rate within the range of 0.03366-0.10885kg/s. Both the compressor and turbine’s temperature and pressure at the inlet and outlet as well as the flow rate are measured and monitored remotely through the control panel. Using electrical control valves and set of sensors, the inlet temperature, pressure could be measured. At the same time, the compressor mass flow rate can be controlled during the test. The main components of the system are shown in Figure 12. Fig.9 Velocity magnitude contours and velocity In this paper, when the compressor wheel speed vectors reached at 160000 rpm, the compressor mass flow rate is then varied while keeping the same turbocharger speed to cover the whole range of operation from the surge to chocking conditions. The compressor output pressure and temperature are recorded using the data acquisition system at each flow rate after at least 3-15 minutes steady operation of the turbocharger.

Fig.10 Mach number contours

3.4 Pressure ratio

CFD simulations were carried out at 4 operating points for an impeller speed of 160000 rpm. The simulated results are shown in table 2 which includes outlet pressure and πc (pressure ratio). Fig.11 FIT company turbocharger test facilities Tab. 2 The values of the CFD parameters

Mass flow Outlet pressure(kPa) πc rate(kg/s) 0.03558 90.526 1.919045 0.06800 80.408 1.817735 0.09983 67.284 1.718576 0.10885 56.330 1.616141

4 Experimental work and discussion The experimental work was carried out at the continuous flow turbocharger test facility available Fig. 12. Schematic layout of No.1 laboratory test Result Comparison facility 2.5

Ratio 2 There are 4 temperature sensors in the inlet and outlet which were marked as ABCD which position 1.5 are shown in figure 12. Also, there are 4 pressure 1 Pressure sensors in the same place as temperature sensors 0.5 named ABCD. 0 0.02 0.04 0.06 0.08 0.1 0.12 Table 3 lists the values of the tested compressor housing parameters. The table shows the outlet Mass Flow Rate (kg/s) pressure of the 4 sensors and calculates pressure Experiment Data CFD Data ratio of the compressor housing using the formulation which is shown below: Fig.13 Result comparison

πc = （P0+Pc2)/(P0+Pc1) 5 Conclusions This paper describes a CFD analysis of the P0 : atmospheric pressure behavior of compressor housing under steady flow Pc1: inlet pressure conditions. The boundary conditions and MRF Pc2: outlet pressure region are introduced in this study to simulate the πc : pressure ratio performance of compressor housing. The inlet boundary conditions are fixed and the outlet Tab. 3 the values of the tested parameters pressure is to be monitored during the simulation. The simulated results show similar performance to Mass flow A(kPa) B(kPa) C(kPa) D(kPa) πc rate the experimental data even though there are some 0.03366 93.975 93.525 93.375 93.300 1.924 deviations in magnitudes of pressure ratio 0.03558 93.675 93.300 93.225 93.000 1.922 particularly at higher mass flow rates as shown in 0.06800 88.200 87.900 87.675 87.450 1.867 0.08700 76.350 75.675 75.900 75.675 1.751 Figure 13. This deviation may be attributed to 0.09983 62.625 62.250 62.175 61.875 1.618 many factors, such as errors on CAD geometry, 0.10885 49.875 49.425 49.425 49.200 1.494 mesh quality, turbulence stresses and computer round off. There are two important mass flow rates points In fact, CFD solutions are more difficult to obtain, including surge and choke points to simulate as as the device figure 13 shows. The figure below shows that operation approaches the surge line. Because different mass flow rate not only presents a steady-state CFD naturally suffers from considerable effect on the pressure and temperature “convergence” issues at the low mass-flows where at the compressor outlet but also affects the air the flow regime becomes unsteady [17]. speed around the compressor wheel. In this study, Further investigations are needed to evaluate the compressor housing pressure ratio drops reasons for this deviation. dramatically in the experiment work which was Acknowledgement tested in the No.1 laboratory which is different The author express thanks to Mr. Chen and Mr. form the CFD data. CFD simulations, which were Wang for supporting this research. Also, wish to carried out at the speed of 160000 rpm, show good thank Mr. Fan for his worthy assistance during the similarity at low mass flow rate with experimental calculations set-up. results while deviation is found to be up to 7.5576% at higher flow rate. References

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