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Research Papers

The Effect of Unequal Admission on the Performance and Loss Generation in a Double-Entry Turbocharger Turbine

[+] Author and Article Information
Colin D. Copeland

Department of Mechanical Engineering, Imperial College London, London, UK, SW7 2AZc.copeland@imperial.ac.uk

Peter J. Newton

Department of Mechanical Engineering, Imperial College London, London, UK, SW7 2AZp.newton03@imperial.ac.uk

Ricardo Martinez-Botas1

Department of Mechanical Engineering, Imperial College London, London, UK, SW7 2AZr.botas@imperial.ac.uk

Martin Seiler

 ABB Turbo Systems Ltd., CH 5401, Baden, Switzerlandemail:martin.a.seiler@ch.abb.com

1

Corresponding author.

J. Turbomach 134(2), 021004 (Jun 22, 2011) (11 pages) doi:10.1115/1.4003226 History: Received September 03, 2010; Revised September 03, 2010; Published June 22, 2011; Online June 22, 2011

The current work investigates a circumferentially divided turbine volute designed such that each gas inlet feeds a separate section of the turbine wheel. Although there is a small connecting interspace formed between the nozzle and the mixed-flow rotor inlet, this design does well to preserve the exhaust gas energy in a pulsed-charged application by largely isolating the two streams entering the turbine. However, this type of volute design produces some interesting flow features as a result of unequal flows driving the turbine wheel. To investigate the influence of unequal flows, experimental data from the turbocharger facility at Imperial College have been gathered over a wide range of steady-state, unequal admission conditions. These test results show a significant drop in turbine performance with increasing pressure difference between inlets. In addition, the swallowing capacities of each gas inlet are interdependent, thus indicating some flow interaction between entries. To understand the flow physics driving the observed performance, a full 3D computational fluid dynamics (CFD) model of the turbine was created. Results show a highly disturbed flow field as a consequence of the nonuniform admission. From these results, it is possible to identify the regions of aerodynamic loss responsible for the measured performance decrease. Given the unequal flows present in a double-entry design, each rotor passage sees an abrupt change in flow conditions as it rotates spanning the two feeding sectors. This operation introduces a high degree of unsteady flow into the rotor passage even when it operates in steady conditions. The amplitude and frequency of this unsteadiness will depend both on the level of unequal admission and the speed of rotor rotation. The reduced frequency associated with this disturbance supports the evidence that the flow in the rotor passage is unsteady. Furthermore, the CFD model indicates that the blade passage flow is unable to fully develop in the time available to travel between the two different sectors (entries).

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 2

Turbine volute arrangement

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Figure 3

Exploded view of the computational domain

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Figure 4

Surface mesh of the nozzle and rotor domains

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Figure 5

Mass parameter versus pressure ratio for the CFD simulations

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Figure 6

Total-to-static efficiency of the CFD simulations in comparison with experiment

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Figure 7

Effective area of the inlet with varying pressures calculated from the CFD simulation (U3/Cis=0.65)

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Figure 8

Effective area of the inlet with constant pressure calculated from the CFD simulation (U3/Cis=0.65)

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Figure 9

Unequal admission efficiency predicted by the CFD in comparison with the experimental efficiency

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Figure 10

Nozzle exit static pressure (normalized by the total pressure of the lower inlet) as a function of the azimuth angle for unequal cases 7 and 9

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Figure 11

Pressure contours normalized against the inlet pressure of the lower entry

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Figure 12

Unwrapped constant 50% span relative velocity contours

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Figure 13

Relative static entropy increase in different areas of the turbine domain

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Figure 14

Entropy generation rate on nozzle midspan

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Figure 15

Entropy generation rate contours on a constant span

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Figure 16

Transient torque on a single blade passage

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