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Research Papers

A Three-Dimensional Computational Study of Pulsating Flow Inside a Double Entry Turbine

[+] Author and Article Information
Peter Newton

Department of Mechanical Engineering,
Imperial College London,
London SW7 2AZ, UK
e-mail: peter.newton03@imperial.ac.uk

Ricardo Martinez-Botas

Department of Mechanical Engineering,
Imperial College London,
London SW7 2AZ, UK
e-mail: r.botas@imperial.ac.uk

Martin Seiler

ABB Turbo Systems Ltd.,
Turbocharging Systems (ZTA),
Bruggerstrasse 71a,
Baden CH-5401, Switzerland
e-mail: martin.a.seiler@ch.abb.com

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 7, 2014; final manuscript received July 11, 2014; published online September 30, 2014. Editor: Ronald Bunker.

J. Turbomach 137(3), 031001 (Sep 30, 2014) (10 pages) Paper No: TURBO-14-1116; doi: 10.1115/1.4028217 History: Received July 07, 2014; Revised July 11, 2014

The double entry turbine contains two different gas entries, each feeding 180 deg of a single rotor wheel. This geometry can be beneficial for use in turbocharging and is uniquely found in this application. The nature of the turbocharging process means that the double entry turbine will be fed by a highly pulsating flow from the exhaust of an internal combustion engine, most often with out-of-phase pulsations in each of the two entries. Until now research on the double entry turbine under pulsating flow conditions has been limited to experimental work. Although this is of great value in showing how pulsating flow will affect the performance of the double entry turbine, the level of detail with which this can be studied is limited. This paper is the first to use a three-dimensional computational analysis to study the flow structures within a double entry turbine under conditions of pulsating flow. The analysis looks at one condition of pulsating flow with out-of-phase pulsations. The computational results are validated against experimental data taken from the turbocharger test facility at Imperial College and a good agreement is found. The analysis first looks at the degree of mass flow storage within different components of the turbine and discusses the effect on the performance of the turbine. Each of the volute limbs is found to be subject to a large degree of mass storage throughout a pulse cycle demonstrating a definite impact of the unsteady flow. The rotor wheel shows a much smaller degree of mass flow storage overall due to the pulsating flow; however, each rotor passage is subject to a much larger degree of mass flow storage due to the instantaneous flow inequality between the two volute inlets. This is a direct consequence of the double entry geometry. The following part of the analysis studies the loss profile within the turbine under pulsating flow using the concept of entropy generation rate. A significant change in the loss profile of the turbine is found throughout the period of a pulse cycle showing a highly changing flow regime. The major areas of loss are found to be due to tip leakage flow and mixing within the blade passage.

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References

Figures

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Fig. 1

Double entry volute

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Fig. 2

Schematic of test facility

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Fig. 3

Measured inlet static pressure

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Fig. 5

Comparison of experimentally measured and computational prediction of mass flow rate, normalized by the peak measured mass flow rate

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Fig. 6

Comparison between experimentally measured pressure within the nozzle–rotor interspace and that predicted by CFD

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Fig. 9

Mass flow discrepancy predicted for a single rotor passage under a 52 Hz out-of-phase pulsation

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Fig. 8

Figure showing the normalized mass flow discrepancy predicted by the CFD model for the inner and outer volute limbs and the rotor wheel under a 52 Hz pulsating flow

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Fig. 7

Comparison of experimental and computational prediction of torque, normalized by the peak experimental torque

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Fig. 11

Division of the entropy generation throughout an entire pulse cycle within the different regions of the rotor wheel

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Fig. 10

Division of the rotor passage for analysis of entropy generation in different regions

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Fig. 12

Figure showing the distribution of entropy generation at points A, B, and C in Fig. 11

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Fig. 13

A snapshot of a plane showing the normalized entropy generation rate per unit volume at point A from Fig. 11

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Fig. 14

A snapshot of a plane showing the normalized entropy generation rate per unit volume at point B from Fig. 11

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Fig. 15

A snapshot of a plane showing the normalized entropy generation rate per unit volume at point C from Fig. 11

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