Abstract
Compared to ordinary rotor, rod fastening rotor has the advantages of lighter weight, higher strength and easier installation, so it is widely used in gas turbine. However, in the process of a long-term operation, the rod may be deformed due to the influence of alternating load, high temperature and other uncertain factors. In serious cases, it can even lead to a major accident. The discontinuous characteristic of rod fastening rotor leads to great differences in dynamic characteristics compared to ordinary rotor. Based on the Herz contact theory and GW contact model, the contact effect between two discs was studied, and the relationship among the contact load, the distance between two disks and the equivalent bending stiffness was obtained. Findings show the bending stiffness to decrease nonlinearly with the decrease in contact load. The lumped mass method was used to establish the rotor model. The contact effect was considered and the Runge–Kutta method was used to solve the model. Combined with the bifurcation diagram, time domain diagram and spectrum diagram, the influence of contact stiffness on rotor dynamic characteristics was analyzed. The results show that the dynamic characteristics of the rod fastening rotor are rich due to the influence of nonlinear factors. In the case of uniform relaxation, the contact stiffness has different effects on the response state and frequency doubling amplitude of the system at different speeds, which is mainly related to the motion state of the system. In the case of non-uniform relaxation, the degree of relaxation does not affect the motion state of the system, but only changes the amplitude of vibration. The results provide theoretical support for condition monitoring and fault diagnosis of rod fastening rotor.
Highlights
Accepted: 28 January 2022Gas turbine is widely used in power generation, aviation industry and other fields because of its high efficiency and high reliability
When the rotating speed is at 500 rad/s, the time domain curve of the angle displacement θ 1 is sinusoidal, and the spectrum diagram has only a component at rotating frequency, which is mainly caused by mass unbalance, and the corresponding bifurcation diagram is in a period one motion state
Affected by the nonlinear oil film force, the spectrum has a component at half of rotating frequency, and this component is greater than the component at rotating frequency, and the corresponding bifurcation diagram is in period two motion state
Summary
Gas turbine is widely used in power generation, aviation industry and other fields because of its high efficiency and high reliability. Amin [4] established a nonlinear model of a gas turbine rotor, fitted the nonlinear stiffness of the bearing, and studied the nonlinear characteristics of the rotor. Liu et al [22] established the dynamic model of a rod fastening rotor-bearing system, studied the system stability using Floquet theory and compared it to ordinary rotor He et al [23] proposed a new method to determine the normal stiffness of the contact surface. Hu et al [24,25,26] studied the nonlinear dynamic response of a two-disk rod fastening rotor with transverse crack, initial bending, rub impact and other faults, and analyzed the influence of system parameters such as speed, crack size, crack angle, contact surface damping coefficient, initial bending and rub impact stiffness on the dynamic characteristics. This study provides a theoretical basis for the design and the fault diagnosis of the rod fastening rotor
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