Abstract
State equations of aircraft engine dynamics usually required for controller design, are not available in closed form, so the dynamic models are commonly linearized numerically. Development of model-based controllers for aeroengine in the recent years necessitates the use of accurate linear models. However, there is no comprehensive study about the accuracy of the linear models obtained from nonlinear engine models. In this paper, the accuracy of different numerical linearization methods for linearizing the dynamic model of a turbofan engine is investigated. For this objective, a thermodynamic model of a two-spool turbofan engine is considered and three various numerical linearization methods are defined. The first method is based on the perturbation technique, including ordinary and central difference perturbation. The second one is a system identification method and the third one is tuning the elements of the matrices of the linear state-space model using genetic algorithm. The accuracy analysis of the presented procedures is performed for both single-input and double-input cases. In the single-input case, the fuel mass flow rate and in the double-input, in addition to the fuel, the bleed air taken from between the two compressors are considered as control variables. Finally, by defining different error criterions, the accuracy of the linearization methods is evaluated. The results show that the linear model obtained from system identification and central difference perturbation methods have higher percentage of compliances compared to the others.
Highlights
A turbofan engine includes various complicated dynamics and behaviors such as the gas flow dynamics in the compressor and turbine, combustion dynamics, the heat transfer dynamics between the gas and the body, the inertia of the shafts, losses, delays and environmental factors [1,2,3]
Among the dynamics existing in the engine, those resulting from gas dynamics, those of sensors and actuators and ignition dynamics are much faster than the others, which are often ignored, but are considered in very accurate and complete models [4,5]
The important point that must surely be considered in the linearization of the engine model is omitting the mean value from the data, because the incremental values of the variables about the operating point are considered in the linear models
Summary
A turbofan engine includes various complicated dynamics and behaviors such as the gas flow dynamics in the compressor and turbine, combustion dynamics, the heat transfer dynamics between the gas and the body, the inertia of the shafts, losses, delays and environmental factors [1,2,3]. Model-based controllers are extensively considered by researchers [12,13,14] Since, in these controllers, the model parameters are directly present in the designed control signal, the accuracy of the model is of great importance. Compressor pressure ratio models has commonly been performed using the perturbation method without presenting an analysis about the accuracy of the linear model [17,18,19,20]. The accuracy of different numerical linearization methods that can be used in linearizing the thermodynamic model of a turbofan engine is investigated. This analysis is performed by defining different error indices in the single-input and double-input cases
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
