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Research Papers: Gas Turbines: Turbomachinery

A Low-Order Model for Predicting Turbocharger Turbine Unsteady Performance

[+] Author and Article Information
Teng Cao

Whittle Laboratory,
University of Cambridge,
Cambridge CB3 0DY, UK
e-mail: tc367@cam.ac.uk

Liping Xu

Whittle Laboratory,
University of Cambridge,
Cambridge CB3 0DY, UK

Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received October 25, 2015; final manuscript received November 29, 2015; published online February 17, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(7), 072607 (Feb 17, 2016) (11 pages) Paper No: GTP-15-1522; doi: 10.1115/1.4032341 History: Received October 25, 2015; Revised November 29, 2015

In this paper, a low-order model for predicting performance of radial turbocharger turbines is presented. The model combines an unsteady quasi-three-dimensional (Q3D) computational fluid dynamics (CFD) method with multiple one-dimensional (1D) meanline impeller solvers. The new model preserves the critical volute geometry features, which is crucial for the accurate prediction of the wave dynamics and retains effects of the rotor inlet circumferential nonuniformity. It also still maintains the desirable properties of being easy to set-up and fast to run. The model has been validated against a experimentally validated full 3D unsteady Reynolds-averaged Navier–Stokes (URANS) solver. The loss model in the meanline model is calibrated by the full 3D RANS solver under the steady flow states. The unsteady turbine performance under different inlet pulsating flow conditions predicted by the model was compared with the results of the full 3D URANS solver. Good agreement between the two was obtained with a speed-up ratio of about 4 orders of magnitude (∼104) for the low-order model. The low-order model was then used to investigate the effect of different pulse wave amplitudes and frequencies on the turbine cycle averaged performance. For the cases tested, it was found that compared with quasi-steady performance, the unsteady effect of the pulsating flow has a relatively small impact on the cycle-averaged turbine power output and the cycle-averaged mass flow capacity, while it has a large influence on the cycle-averaged ideal power output and cycle-averaged efficiency. This is related to the wave dynamics inside the volute, and the detailed mechanisms responsible are discussed in this paper.

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Figures

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Fig. 1

Illustrations of the introduced Q3D model

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Fig. 2

Volute mesh generated by the Q3D model

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Fig. 3

Calibrations of the Q3D model under steady state: (a)mass flow against pressure ratio and (b) efficiency against velocity ratio

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Fig. 4

Detailed comparisons of the rotor inlet conditions between the Q3D model and the full 3D CFD: (a) total pressure and (b) absolute flow angle

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Fig. 5

Comparisons of the prediction of turbine instantaneous mass flow capacity given by the Q3D model and the full 3D CFD: (a) fr=0.22, (b) fr=0.44, and (c) fr=0.65

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Fig. 6

Comparisons of the prediction of turbine instantaneous power output given by the Q3D model and the full 3D CFD: (a) fr=0.22, (b) fr=0.44, and (c) fr=0.65

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Fig. 7

Variations of the local pressure corrected Strouhal number of the turbine rotor

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Fig. 8

Quasi-steady turbine performance evaluation process

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Fig. 9

Comparison of the instantaneous inlet mass flow capacity under pulsating flow (Λ = 0.62) and quasi-steady flow conditions

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Fig. 10

Lambda number (Λ) of the studied cases

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Fig. 11

Comparison of the cycle-averaged turbine performance under pulsating and quasi-steady flow conditions

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Fig. 12

Comparison of the instantaneous rotor efficiency under pulsating flow (Λ = 0.62) and quasi-steady flow conditions

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Fig. 13

Breakdown of the contribution of each period to the total efficiency deviation from quasi-steady efficiency

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Fig. 14

Breakdown of the time-integrated lost power within the rotor during different unsteady phases

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