Research On Dynamic Characteristics And Fault Feature Extraction Methods Of A Cracked Rotor With Elastic Supports

Aeroengines and gas turbines as the core power plants in the field of aviation,large surface warship and clean power generation.Its reliability and safety requirements are extremely high.The engine rotor system is prone to cracks due to the continuous harsh and variable load.With the expansion of the crack,it will affect the normal stable operation of the power unit.Meanwhile,it has become a potentially huge security risk.Therefore,it is of great significance to diagonose the cracked rotor based on the vibration signal.In this paper,the relationship between strain energy release rate and stress intensity factor is established based on the expression of various types of stress intensity factors.Combining the Castingliano's theorem and the coordinate system transformation matrix,the stiffness of cracked unit in the fixed coordinate system is obtained by the means of the Dimarogonas method.However,a truly breathing behaviour can be represented by taking into account the gradual opening and closing of the crack using the stress intensity factor at the crack front at each instant and then finding the amount of crack opening.During the research,a gas turbine modeled rotor is considered.The influence of crack depths,inclination angles,the front shape of the crack,unbalanced forces and rotational speed on the breathing and time-varying characteristics of the element stiffness are discussed.Aims at the open and breathing crack,the influence of the above parameters on their vibration response characteristics,critical speed,etc.are studied separately.At the same time,the similarities and differences of the two models are compared.The results shows that the appearance of crack increases the 1x frequency vibration of the rotor and brings about obvious 2X frequency component,even greater than the 1x frequency.As the crack weakens the stiffness of the rotor,it leads to a decrease in the critical speed of the rotor systerm and at the same time it causes subcritical resonance.And when the crack is located in a larger modal vibration shape of the rotor,the influence of the critical speed is greater.Finally,according to the characteristics of crack faults obtained by the simulation,taking an actual cracked rotor as an example,combining fault diagnosis theory and feature extraction method,a crack rotor fault feature analysis is carried out.