Research Papers: Gas Turbines: Turbomachinery

The Effect of Gas Models on Compressor Efficiency Including Uncertainty

[+] Author and Article Information
Fangyuan Lou

Research Assistant
e-mail: louf@purdue.edu

John Fabian

e-mail: fabian@purdue.edu

Nicole L. Key

Associate Professor
e-mail: nkey@purdue.edu
Purdue University,
500 Allison Road,
West Lafayette, IN 47907

Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received August 6, 2013; final manuscript received August 21, 2013; published online October 22, 2013. Editor: David Wisler.

J. Eng. Gas Turbines Power 136(1), 012601 (Oct 22, 2013) (8 pages) Paper No: GTP-13-1297; doi: 10.1115/1.4025317 History: Received August 06, 2013; Revised August 21, 2013

Since isentropic efficiency is widely used in evaluating the performance of compressors, it is essential to accurately calculate this parameter from experimental measurements. Quantifying realistic bounds of uncertainty in experimental measurements are necessary to make meaningful comparisons to computational fluid dynamics simulations. This paper explores how the gas model utilized for air can impact not only the efficiency calculated in an experiment, but also the uncertainty associated with that calculation. In this paper, three different gas models are utilized: the perfect gas model, the ideal gas model, and the real gas model. A commonly employed assumption in calculating compressor efficiency is the perfect gas assumption, in which the specific heat, is treated as a constant and is independent of temperature and pressure. Results show significant differences in both calculated efficiency and the resulting uncertainty in efficiency between the perfect gas model and the real gas model. The calculated compressor efficiency from the perfect gas model is overestimated, while the resulting uncertainties from the perfect gas model are underestimated. The ideal gas model agrees well with the real gas model, however. Including the effect of uncertainty in gas properties results in very large uncertainties in isentropic efficiency, on the order of ten points, for low pressure ratio machines.

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Fig. 1

Specific heat calculated from different gas models

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Fig. 2

Calculated isentropic efficiency from different gas models

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Fig. 3

Sketch of uncertainty propagation for isentropic efficiency

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Fig. 4

Uncertainty in isentropic efficiency for different temperature measurement uncertainties for the: (a) perfect gas model using inlet conditions; (b) perfect gas model using average conditions; (c) ideal gas model; and (d) real gas model

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Fig. 5

Uncertainty in isentropic efficiency with varying uncertainties in pressure for the: (a) perfect gas model using inlet conditions; (b) perfect gas model using average conditions; (c) ideal gas model; and (d) real gas model

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Fig. 6

Uncertainty in isentropic efficiency for different pressure measurement uncertainties at different pressure ratios using the real gas model

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Fig. 7

Relation of uncertainty in isentropic efficiency calculated from the real gas model with varying uncertainties in temperature

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Fig. 8

Relation of uncertainty in isentropic efficiency calculated from the ideal gas model with varying uncertainties in temperature




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