Research Papers: Flows in Complex Systems

Computational Fluid Dynamics Analysis of a Radial Turbine During Load Step Operation of an Automotive Turbocharger

[+] Author and Article Information
Harald Roclawski, Martin Böhle

Department of Mechanical Engineering,
Institute of Fluid
Mechanics and Turbomachinery,
Technical University of Kaiserslautern,
Kaiserslautern 67663, Germany
e-mail: roclawsk@mv.uni-kl.de

Marc Gugau

BorgWarner TurboSystems Engineering GmbH,
Kirchheimbolanden 67292, Germany
e-mail: mgugau@borgwarner.com

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received July 22, 2016; final manuscript received September 19, 2017; published online October 19, 2017. Assoc. Editor: Olivier Coutier-Delgosha.

J. Fluids Eng 140(2), 021102 (Oct 19, 2017) (9 pages) Paper No: FE-16-1474; doi: 10.1115/1.4037975 History: Received July 22, 2016; Revised September 19, 2017

A method for evaluating the transient performance of a turbocharger (TC) is so-called load step tests. In these tests, the load of the engine is increased at constant engine speed and the time measured from the start to the end of the load step is measured. Usually, these tests can be run relatively late in the development process, since hardware needs to be already available. In order to judge the transient TC performance at an earlier stage, engine process simulations are run using maps of compressor and turbine. For the turbine, these maps usually need to be extrapolated, since only a certain range of each speed line can be measured on a standard gas stand. Furthermore, because of the exhaust gas pulsation of the engine, it is known that the turbine performance differs from the steady-state case which the maps rely on. This has to be respected by additional models. Using computational fluid dynamics (CFD) simulations, the transient performance of the turbine can be analyzed independent from steady-state maps. So far, these investigations have been usually performed with a constant turbine speed. In this paper, a method is presented which includes the speed fluctuations of the TC caused by the exhaust pulsations as well as the change in mean speed during the load step by including compressor and engine in the CFD analysis with User-Fortran models. Results for a load step from 21,000 rpm to 196,400 rpm are discussed.

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Fig. 1

Fitting of efficiency curves

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Fig. 2

Operating point of compressor

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Fig. 3

Pulse shapes during the load step

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Fig. 4

Friction loss model

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Fig. 5

Schematic of load step simulation

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Fig. 6

CFD model of radial turbine

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Fig. 7

Turbocharger speed during loadstep simulation

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Fig. 8

Steady-state conditions at start of loadstep

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Fig. 9

Compressor operating points

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Fig. 10

Compressor pressure ratio

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Fig. 11

Compressor and turbine power

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Fig. 12

Acceleration power

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Fig. 13

Turbine map and hysteresis loops for selected operating points

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Fig. 14

Map of turbine wheel without volute and hysteresis loops for selected operating points

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Fig. 15

Absolute and incidence angle at turbine wheel inlet

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Fig. 16

Streamlines at 50% span at t = 0.743−0.75 s

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Fig. 17

Streamlines at 50% span at t = 1.664 − 1.669 s

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Fig. 18

Streamlines at 50% span at t = 3.269 − 3.273 s

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Fig. 19

Axial thrust of turbine wheel during load step




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