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Research Papers: Gas Turbines: Aircraft Engine

First and Second Law Analysis of Intercooled Turbofan Engine

[+] Author and Article Information
Xin Zhao

Fluid Dynamics Division,
Applied Mechanics Department,
Chalmers University of Technology,
Göteborg 41296, Sweden
e-mail: zxin@chalmers.se

Oskar Thulin

Fluid Dynamics Division,
Applied Mechanics Department,
Chalmers University of Technology,
Göteborg 41296, Sweden
e-mail: oskar.thulin@chalmers.se

Tomas Grönstedt

Fluid Dynamics Division,
Applied Mechanics Department,
Chalmers University of Technology,
Göteborg 41296, Sweden
e-mail: tomas.gronstedt@chalmers.se

Contributed by the Aircraft Engine Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 13, 2015; final manuscript received August 3, 2015; published online September 16, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(2), 021202 (Sep 16, 2015) (8 pages) Paper No: GTP-15-1276; doi: 10.1115/1.4031316 History: Received July 13, 2015; Revised August 03, 2015

Although the benefits of intercooling for aero-engine applications have been realized and discussed in many publications, quantitative details are still relatively limited. In order to strengthen the understanding of aero-engine intercooling, detailed performance data on optimized intercooled (IC) turbofan engines are provided. Analysis is conducted using an exergy breakdown, i.e., quantifying the losses into a common currency by applying a combined use of the first and second law of thermodynamics. Optimal IC geared turbofan engines for a long range mission are established with computational fluid dynamics (CFD) based two-pass cross flow tubular intercooler correlations. By means of a separate variable nozzle, the amount of intercooler coolant air can be optimized to different flight conditions. Exergy analysis is used to assess how irreversibility is varying over the flight mission, allowing for a more clear explanation and interpretation of the benefits. The optimal IC geared turbofan engine provides a 4.5% fuel burn benefit over a non-IC geared reference engine. The optimum is constrained by the last stage compressor blade height. To further explore the potential of intercooling the constraint limiting the axial compressor last stage blade height is relaxed by introducing an axial radial high pressure compressor (HPC). The axial–radial high pressure ratio (PR) configuration allows for an ultrahigh overall PR (OPR). With an optimal top-of-climb (TOC) OPR of 140, the configuration provides a 5.3% fuel burn benefit over the geared reference engine. The irreversibilities of the intercooler are broken down into its components to analyze the difference between the ultrahigh OPR axial–radial configuration and the purely axial configuration. An intercooler conceptual design method is used to predict pressure loss heat transfer and weight for the different OPRs. Exergy analysis combined with results from the intercooler and engine conceptual design are used to support the conclusion that the optimal PR split exponent stays relatively independent of the overall engine PR.

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References

Figures

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Fig. 1

IC (above centerline) and non-IC (below centerline) geared engine impression

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Fig. 2

Two-pass cross flow tubular intercooler

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Fig. 3

Involute spiral tubes configuration installation

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Fig. 4

Intercooler external side configuration

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Fig. 5

Engine components exergy destruction per unit time

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