Testing and Modelling Gas Turbines Using Multisine Signals and Frequency-Domain Techniques

Abstract

The frequency-domain identification of gas turbine dynamics is discussed. Models are directly estimated from engine data and used to validate linearised thermodynamic models derived from the engine physics. This work is motivated by the problems previously • encountered when using time-domain methods. A brief overview of frequency-domain techniques is presented and the design of appropriate multisine test signals is discussed. Practical results are presented for the modelling of the fuel feed to shaft speed dynamics of a twin-spool engine. The gathered data are analysed and the frequency response functions of the engine are estimated. The identification of parametric s-domain models is discussed in detail and a comparison made between the identified models and the linearised thermodynamic models. The influence of engine nonlinearities on the linear models is also examined.

Assessing the Errors in Practical Gas Turbine Modelling

“…1. This was the final figure of the previous paper (Evans, 1998) and illustrates the variation of the pole and zero positions with operating point. It is clear from these results that the thermodynamic models are not adequately representing the dynamics of either shaft at higher operating points and that the second-order dynamics of the LP shaft are also badly represented.…”

“…A related paper was presented at the last ASME Gas Turbine Conference (Evans, 1998), which discussed the results of testing an aircraft gas turbine with multisine signals and directly estimating linear engine models in the frequency domain. The paper noted that both noise and nonlinearities would influence the estimated models but did not present a detailed analysis of these effects, or attempt to quantify their influence.…”

Multivariable Modelling of Gas Turbine Dynamics

“…The identification is conducted in the frequency domain, which allows s-domain multivariable models to be directly estimated. The work is an extension of that previously conducted on the identification of transfer-function models, which was presented at previous ASME gas turbine conferences [1,2] and has been published in a number of recent journal papers [3][4][5].…”

Global Nonlinear Modelling of Gas Turbine Dynamics Using NARMAX Structures

“…Parametric identification involves estimating continuous sdomain models with a pure time delay T d [10,11]. Parametric models were estimated at each operating point, using a model selection and validation procedure which has been described in detail in [2][3][4][5]…”

“…Recent work by Evans et al [2][3][4][5] concentrated on testing the engine using small-amplitude multisine signals and then using frequency-domain techniques to identify linear models of high accuracy. The errors due to noise and nonlinearities were assessed and found to be small for these small-signal models.…”