`International Journal of Rotating MachineryVolume 6, Issue 5, Pages 333-343http://dx.doi.org/10.1155/S1023621X00000312`

## Numerical Analysis of Dynamic Properties of Nonlinear Rotor Systems of Aircraft Jet Engines

1Brno Military Academy, Kounicova 65, PS 13, Brno 61200, Czech Republic
2Faculty of Mechanical Engineering, Institute of Solid Mechanics, Brno Technical University, Technická 2, Brno 61669, Czech Republic
3Ostrava Technical University, 17 Listopadu, Ostrava 72100, Czech Republic

Received 23 April 1998; Revised 16 December 1998

Copyright © 2000 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### Abstract

The paper deals with a manner of modelling and results of the calculation of dynamic properties and vibrations of the double spool aircraft turbofan engine AI-25, used in aeroplanes L-39 (Albatross). The calculations take into account the flexibilities of the engine's both coaxial rotors, their supports (including their hydrodynamic dampers), and its casing as well. Besides the short description of the engine design peculiarities and of its calculating model, there is also a short description of the used method of calculations, with focus on its peculiarities as well. Finally, some results of calculations and conclusions that follow from them are presented.

The calculating model of the engine is considered as a dynamic system that consists of two coaxial rotors, their flexible supports, and the engine casing. The model respects nonlinear elements between rotating and nonrotating parts of the engine, such as e.g., the oil squeeze damper, the labyrinth sealing, etc. The rotor system is considered as rotationally symmetric and with internal material damping. The basic calculating model is based on the finite elements method (FEM). For the more demanding nonlinear problems which would allow to respect also the flexibilities of the engine stator parts and especially their experimentally obtained data, the method of dynamic compliances was found to be more successful. It was also found that the nonlinear problems of complicated rotor systems require special algorithms of calculations to be applied.