Research On Dynamic Behaviors Of A Rotor-bearing System With Crack Faults

Modern turbomachinery is designed in high speed, high flexibility and high efficiency. The improvement of the performance of turbomachinery has led to severely stressed rotors, therefore, the rotor system requests best design and manufacture. However, with several locations where stresses (both mechanical and thermal) can increase despite best design practices, fatigue cracks are always a possibility in such rotors. If undetected early, such cracks can pose a potential source of catastrophic failures. Thus, it has great significance to study the dynamic behaviors of a rotor-bearing system with crack faults for condition monitoring and forecast.The finite element model of the rotor system with transverse, slant and semi-parabolic slant crack were first setup based on finite element method. This paper mainly studies the dynamic behaviors of a single span rotor system with two discs at different crack parameters under two supporting conditions:elastomeric bearing and oil film bearing. Firstly, based on fracture mechanics and castigliano’s method, the stiffness matrix of each crack element was ealeulated and the motion equation of the rotor system is deduced. The crack breathing behavior is represented by using stress intensity factors. The flexibility curve is verified by the results of the paper, which illustrate the correct of the crack deduce in our paper.Secondly, a simple Jeffcott rotor modal in the paper is presented, and based on it, the variation of flexibility coefficients for different crack closure line position is verified by the results of the paper. The law of stiffness variation of transverse, slant and semi-parabolic slant crack under the same and different crack depth is studied. The law of inherent characteristics of the crack rotor system is analyzed at different positions of crack element and crack depth. Meanwhile, dynamic behaviors of the three crack forms are researched at two loading conditions:mass eccentricity and torsional excitation.Finally, the dynamic behaviors at horizontal and torsional directions of a two discs rotor system with transverse, slant and semi-parabolic slant crack under elastomeric bearing, and the influence of the crack parameters, such as the position of crack element, eccentricity of disk, depth of crack and so on, on the dynamic response of the crack rotor. Meanwhile, the dynamic behaviors at horizontal and torsional directions of the crack rotor at different eccentric phase difference between two discs are researched under oil forces bearings. Furthermore, when the acceleration of the crack rotor system is constant, the transient response is analyzed at horizontal and torsional directions of the three crack forms rotor system under elastomeric bearing and oil film bearing, respectively.