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Research Papers

A Method of Map Extrapolation for Unequal and Partial Admission in a Double Entry Turbine

[+] Author and Article Information
Peter Newton

Department of Mechanical Engineering,
Imperial College,
London SW7 2BX, UK

e-mail: peter.newton03@imperial.ac.uk

Alessandro Romagnoli

Department of Mechanical Engineering,
Imperial College,
London SW7 2BX, UK

e-mail: a.romagnoli@imperial.ac.uk

Ricardo Martinez-Botas

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

Colin Copeland

Department of Mechanical Engineering,
University of Bath,
Bath BA2 7AY, UK
e-mail: c.d.copeland@bath.ac.uk

Martin Seiler

ABB Turbo Systems,
Baden 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 August 28, 2013; final manuscript received September 2, 2013; published online November 28, 2013. Editor: Ronald Bunker.

J. Turbomach 136(6), 061019 (Nov 28, 2013) (11 pages) Paper No: TURBO-13-1203; doi: 10.1115/1.4025763 History: Received August 28, 2013; Revised September 02, 2013

This paper presents a method for prediction of the unequal admission performance of a double entry turbine based on the full admission turbine maps and a minimal number of unequal admission points. The double entry turbine has two separate inlet ports which feed a single turbine wheel: this arrangement can be beneficial in a turbocharger application; however the additional entry does add complexity in producing a complete turbine map which includes unequal admission behavior. When a double entry turbine is operated under full admission conditions, with both entries feeding the turbine equally, this will act effectively as a single entry device and the turbine performance can be represented by a standard turbine map. In reality a multiple entry turbine will spend the majority of time operating under varying degrees of unequal admission, with each entry feeding the turbine different amounts; the extent of this inequality can have a considerable impact on turbine performance. In order to produce a full map which extends from full admission through to the partial admission case (where one inlet has no flow) a large number of unequal admission data points are required. The paper starts by discussing previous attempts to describe the partial and unequal admission performance of a double entry turbine. The full unequal admission performance is then presented for a nozzled, double entry turbine. The impact of unequal admission on turbine performance is demonstrated. Under some conditions of operation, the turbine efficiency may be less than half that of the equivalent full admission case based on the average turbine velocity ratio. A method of using the steady, equal admission maps, with a limited number of unequal admission data points, to predict the full unequal admission behavior is presented. A good agreement is found when the map extension method is validated against the full unequal admission turbine performance measured on a test stand. In the prediction of efficiency a mean error of approximately 0.39% is found between the test stand data and the proposed extrapolation method, with a standard deviation of 2.79%. A better agreement is generally found at conditions of higher power.

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References

Watson, N., and Janota, M. S., 1982, Turbocharging the Internal Combustion Engine, Macmillan, London.
Copeland, C. D., Seiler, M., and Martinez-Botas, R. F., 2012, “Unsteady Performance of a Double Entry Turbocharger Turbine With a Comparison to Steady Flow Conditions,” ASME J. Turbomach., 134(2), p. 021022. [CrossRef]
Copeland, C. D., Seiler, M., and Martinez-Botas, R. F., 2011, “Comparison Between Steady and Unsteady Double-Entry Turbine Performance Using the Quasi-Steady Assumption,” ASME J. Turbomach., 133(2), p. 031001. [CrossRef]
Copeland, C. D., Newton, P., Seiler, M., and Martinez-Botas, R. F., 2012, “The Effect of Unequal Admission on the Performance and Loss Generation in a Double-Entry Turbocharger Turbine,” ASME J. Turbomach., 134(2), p. 021004. [CrossRef]
Copeland, C., 2010, “The Evaluation of Steady and Pulsating Flow Performance of a Double-Entry Turbocharger Turbine,” Ph.D. thesis, Imperial College of Science, Technology, and Medicine, University of London, London, UK.
Pischinger, F., and WunscheA., 1977, “The Characteristic Behaviour of Radial Turbines and Its Influence on the Turbocharging Process,” 12th International Congress on Combustion Engines, Tokyo, May 23–27.
Timmis, P. H., 1969, “A Study of the Performance of a Twin Entry Radial Turbine Operating Under Steady and Unsteady Flow Conditions,” M.Sc thesis, University of Manchester, Institute of Science and Technology, Manchester, UK.
Benson, R. S., and Scrimshaw, K. H., 1965, “An Experimental Investigation of Non-Steady Flow in a Radial Gas Turbine,” IMechE Conf. Proc., 180(10), pp. 74–85. [CrossRef]
Newton, P., Copeland, C., Martinez-Botas, R. F., and Seiler, M., 2012, “An Audit of Aerodynamic Loss in a Double Entry Turbine Under Full and Partial Admission,” Int. J. Heat Fluid Flow, 33, pp. 70–80. [CrossRef]
Romagnoli, A., Copeland, C. D., Martinez-Botas, R. F., Rajoo, S., Seiler, M., and Costall, A., “Comparison Between the Steady Performance of Double-Entry and Twin-Entry Turbocharger Turbines,” ASME Paper No. GT2011-45525. [CrossRef]
Szymko, S., 2006, “The Development of an Eddy Current Dynamometer for Evaluation of Steady and Pulsating Turbocharger Turbine Performance,” Ph.D. thesis, Imperial College of Science, Technology, and Medicine, University of London, London, UK.
Rajoo, S., 2007, “Steady and Pulsating Performance of a Variable Geometry Mixed Flow Turbocharger Turbine,” Ph.D. thesis, Imperial College of Science, Technology, and Medicine, University of London, London, UK.
Salim, W.S-I.W., Pesiridis, A., and Martinez-Botas, RF., 2012, “Turbocharger Matching Methodology for Improved Exhaust Energy Recovery,” IMechE 10th International Conference Turbochargers and Turbocharging, London, May 15–16.

Figures

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Fig. 1

The double entry turbine

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Fig. 2

Test facility layout

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Fig. 3

Full admission turbine efficiency characteristic for five different speed lines from 26.9 – 48.3 rps/K

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Fig. 4

Full admission mass flow characteristic for the double entry turbine

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Fig. 5

A three-dimensional color coded plot showing the efficiency of the turbine over the full range of equal and unequal operation. One plane is shown at U/CIS – 0.65, corresponding the peak efficiency velocity ratio in equal admission, the other plane dissects the plot through PR inner = PR outer.

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Fig. 6

Comparison of the full admission efficiency characteristic to that of partial admission, a considerable impact of partial admission operation is observed

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Fig. 7

A plot illustrating the effect of unequal admission on the turbine efficiency for several different loading conditions of the turbine corresponding to average velocity ratios of0.55, 065 and 0.8 at a constant speed of 43.0 rps/K

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Fig. 8

Mass flow characteristics of the turbine under inequal admission, the full admission swallowing capacity of one turbine limb is compared to the swallowing capacity of each limb under inequal admission

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Fig. 9

Plot showing a comparison of the extrapolation function for the full admission efficiency characteristic compared to the measured full admission performance

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Fig. 10

Plot showing a comparison of the extrapolation function for the turbine mass flow parameter compared to the measured full admission performance against velocity ratio

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Fig. 11

Plot showing a comparison of the extrapolation function for the turbine mass flow parameter compared to the measured full admission performance against pressure ratio

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Fig. 12

Comparison of the measured total mass flow across both turbine entries under unequal admission compared to that predicted by the full admission turbine characteristics

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Fig. 13

A comparison of the mass flow ratio (Eq. (7)) calculated using the full admission turbine characteristics for each limb to that measured on the test facility

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Fig. 14

Mass flow predicted through each limb, when using the full admission turbine map along with the relationship given by Eq. (13), compared to that measured on the test facility

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Fig. 15

Figure showing the delivered shaft power (normalized by the peak measured power) predicted by the full admission maps (diamonds) and the extrapolated “negative efficiency” region (crosses) plotted against pressure ratio at a constant speed of 43.0 rps/K

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Fig. 16

Figure showing the theoretical effect of unequal admission on efficiency if the two turbine entries are treated as separate turbines

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Fig. 17

Efficiency ratio (Eq. (14) plotted against the efficiency parameter (Eq. (16)). A clear trend is identified which can be approximated by a function (Eq. (17)).

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Fig. 18

Process flow chart for the prediction of turbine performance given any condition of unequal admission

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