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Research Papers: Gas Turbines: Cycle Innovations

A Sub-idle Compressor Characteristic Generation Method With Enhanced Physical Background

[+] Author and Article Information
Pavlos K. Zachos

Department of Power and Propulsion, School of Engineering, Cranfield University, Cranfield, Bedfordshire MK43 0AL, UKp.zachos@cranfield.ac.uk

Ioanna Aslanidou

Department of Power and Propulsion, School of Engineering, Cranfield University, Cranfield, Bedfordshire MK43 0AL, UKi.aslanidou@cranfield.ac.uk

Vassilios Pachidis

Department of Power and Propulsion, School of Engineering, Cranfield University, Cranfield, Bedfordshire MK43 0AL, UKv.pachidis@cranfield.ac.uk

Riti Singh

Department of Power and Propulsion, School of Engineering, Cranfield University, Cranfield, Bedfordshire MK43 0AL, UKr.singh@cranfield.ac.uk

J. Eng. Gas Turbines Power 133(8), 081702 (Apr 07, 2011) (8 pages) doi:10.1115/1.4002820 History: Received May 27, 2010; Revised July 06, 2010; Published April 07, 2011; Online April 07, 2011

Sub-idle is a very challenging operating region as the performance of a gas turbine engine changes significantly compared with design conditions. In addition, the regulations for new and existing engines are becoming stricter and the prediction of engine relight capability is essential. In order to predict the performance of an engine, detailed component maps are required. The data obtained from rig tests are insufficient at low speeds, creating the need for generation of maps within the sub-idle regime. The first step toward this direction is the use of an extrapolation process. This is a purely mathematical process and the results are not usually of sufficient accuracy. In addition, this method does not provide any insight on the physical phenomena governing the operation of the compressor at low speeds. The accuracy of the resulting compressor map can be increased with a better low speed region definition; this can be achieved via the thorough study of a locked rotor compressor, enabling the derivation of the zero rotational speed line and allowing an interpolation process for the generation of the low speed part of the characteristic. In this work, an enhanced sub-idle compressor map generation technique is proposed. The suggested methodology enables the generation of characteristics at far off-design conditions with enhanced physical background. Alternative parameters for map representation are also introduced. Provided that the all the blade rows of the compressor are of known geometry, a numerical analysis is used for the calculation of the characteristic of the half stage and a stage stacking method is employed to create the entire compressor characteristic. This way, the sub-idle region of the map can be calculated through interpolation, which provides a more accurate and predictive technique. Application of the method for compressor map generation showed that the proposed interpolation approach is robust and capable of enhancing any performance simulation tool used for the prediction of transient altitude relight or ground-starting maneuvers.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Compressor operating modes at low speeds

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Figure 2

Efficiency and enthalpy at low speed conditions (3)

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Figure 3

Characteristic generation method overview on a conventional compressor map

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Figure 4

Forces and velocities in a blade cascade (19)

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Figure 5

Forces on a compressor blade at design (left) and at locked rotor conditions (right)

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Figure 6

Flow midspan flow field of an annular high pressure compressor (HPC) cascade at locked rotor conditions (21)

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Figure 11

Low speed area of the interpolated characteristic in terms of nondimensional mass flow and pressure ratio of an axial high pressure compressor

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Figure 12

Interpolated characteristic in terms of nondimensional mass flow and specific torque for an axial high pressure compressor

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Figure 13

Low speed area of the interpolated characteristic in terms of nondimensional mass flow and specific torque for an axial high pressure compressor

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Figure 10

Interpolated characteristic in terms of nondimensional mass flow and pressure ratio for an axial high pressure compressor

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Figure 9

Zero speed line calculation using stage stacking

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Figure 8

Overview of characteristic generation approaches

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Figure 7

Flow diagram of map generation methodology

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