A Physically Enhanced Method for Sub-Idle Compressor Map Generation and Representation

Sub-idle is a very challenging operating region, as the performance of a gas turbine engine changes significantly compared to 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 is insufficient at low speeds, creating the need for generation of maps within the sub-idle regime. The first step towards 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. The application to compressor maps showed that the methodology proposed is robust and capable to enhance any performance simulation tool used for the prediction of transient altitude relight or groundstarting manoeuvres.Copyright © 2010 by ASME