8. Conclusion

consumption is explained by increased turbine clearances due to the delay in disk warming-up. In contrast, the NDM curve does not manifest a visible overshoot, and the transient process is by far shorter. One can make the same conclusion analyzing the plots of a high-pressure rotor speed in Figure 13: the ENDM curve better fits experimental data, in particular, better reflects the effect of increased clearances. The thrust is the principal parameter of a turbofan. However, under the control law nLP = const used in the experiments, it is constant as well, and the increased clearances are compensated by the additional fuel consumption observed in

High-pressure rotor speed dynamics (1—experimental data; 2—ENDM; 3—NDM).

To show the impact of the clearances dynamically changed on the thrust, the simulation of the turbofan under the control law of a constant low pressure turbine temperature was performed. Figure 14 shows the thrust simulated by both models. It can be seen that, during the first 5 s of intensive engine dynamics, both models are equal. Then, the NDM thrust remains constant, whereas the ENDM thrust

Figure 12.

Figure 14.

170

Thrust dynamics (1—ENDM; 2—NDM).

Figure 13.

Aerospace Engineering

This chapter describes a novel method to enhance a detailed physics-based nonlinear gas turbine model widely used for the aims of aircraft engine control and diagnostics. The method allows us to solve the issue of the impact of varying turbine tip clearances on the dynamic engine performance. This issue is especially important for the engines of maneuverable aircrafts.

Using the proposed method, an enhanced nonlinear dynamic model of a turbofan engine for a maneuverable aircraft has been developed on the basis of an initial nonlinear dynamic model and a simplified dynamic clearance model created with the results of the finite element simulation of turbine parts. The comparison with the initial model and experimental data confirmed a drastic improvement of the accuracy of dynamic gas turbine simulation.
