Proceedings of COBEM 2005 18th International Congress of Mechanical Engineering Copyright © 2005 by ABCM November 6-11, 2005, Ouro Preto, MG GAS TURBINE IDENTIFICATION WITH LINEAR AND NON-LINEAR TECHNIQUES Daniel Pozzani CTA/ITA/IEM – CEP 12228-900 – FAX: +55-12-3947-5911, São José dos Campos – SP _Brazil. danielpozzani@ita.br Luiz C. S. Góes, João R. Barbosa, Marco A. Alves CTA/ITA/IEM – CEP 12228-900 – FAX: +55-12-3947-5911, São José dos Campos – SP _Brazil. goes@ita.br , barbosa@ita.br , maurelio@ita.br Abstract. The discussion present in this paper explains how identification can be applied on gas turbine dynamics, considering a single-spool gas turbine. This gas turbine have one shaft, with a centrifugal compressor and an axial turbine. Its dynamic behavior have linear and non-linear characteristics, where the non-linear behavior presents some dificulties in construct a complete gas turbine model. Some linear models provide tolerable transient behavior to the identification, such rotor, pressure and temperature dynamics. These dynamics characteristics can be described by linear identification, such as Box-Jenkins and Output-error models. This models can only present linear dynamics, and it’s applicable only to small disturbances around a design point. To realize a non-linear identifcation a Narmax identification is adopted to obtain a wide range model, and a comparison between the linear and non-linear models is important to distinguish the main features in both identifications. The identifications are made in an open-loop engine, with especific manipulations in the fuel range to obtain the different dynamic features. Firstly a linear identification is obtained, acquiring a significant number of important models to design and off-design point operation. To the non- linear identification, a Narmax identification is proposed, with posterior simulations and satisfatorial validation of both linear and non-linear models. Keywords: gas turbine model, identification, linear, non-linear, design point, transient behavior. 1. Introduction Gas turbines are rotating machines that convert fuel energy in mechanical work, sometimes to provide shaft power in an electrical generation duty, sometimes to supply thrust during aircraft flight and maneuvering. The considered aeronautical single-spool gas turbine is compounded by an air intake, a centrifugal compressor, anular combustion chamber, axial turbine and an exhaust nozzle, with a shaft that links the compressor with the turbine. The components features of the gas turbine are illustrated in Fig. 1. The colors differentiate the engine sections. Figure 1 Single-spool gas-turbine. Gas turbine modeling has been a key factor for its dynamic investigation, and great efforts are realized to aim the construction of more and more complex models that delineate and accomplish the dynamic behavior of these thermodynamic systems. High costs and expensive investments in developing new gas turbines guided to an undesirable commercial risk. By this fact, a high fidelity acquisition of a model more accurate is crucial to analyze and predict the engine performance without over arising costs with prototypes and aiming control laws development to the engine and optimize commercial parameters like fuel consumption or material quantity used to construct the metallic structure. All of these items are to carry out with the limited requirements demanded by the clients, project requirements, certification entities and environmental laws.