Design Of Simulation Bench For Rotor System With Cracked Blade And Analysis Of Torsional Vibration Characteristics

In this paper,in view of the urgent need for rapid diagnosis of long blade crack faults in steam turbines and blade crack faults in large fans,based on the classical methods that the blade shaft system is simplified into a rotor disk model and the cracked blade is simplified into a beam model in the rotating machinery,this paper coupled the blades to the rotor shafting,then found that the symmetrical blades have inherent frequency repeated roots and anisotropic vibrations.Unlike the traditional method of monitoring the rotor shaft displacement using eddy current transducer,a method of measuring the torsional vibration of the shaft system with a magnetoelectric sensor was proposed to find the characteristics of cracked blades.The main works of the paper were:The paper deduced the transfer matrix of a cantilever beam with cracks,and established the actual boundary conditions to obtain the corresponding frequency equations,then found the inherent frequency of the first-order bending of the cantilever beam with cracks,and analyzed the effect of the depths and positions of the normally-open cracks on the inherent frequencies of the blades by using the finite element method.The rotor-blade experimental bench was designed and built.The dynamic model of the rotor-blade coupling system was established by using the finite element method,and the inherent frequencies and vibration modes of the rotor-blades were obtained.After testing the torsional vibration of the experimental platform shafting,the accuracy of the calculation model and the validity of the calculation method were verified.In order to facilitate the rapid calculation of the torsional vibration of the rotor-blade system,the lumped parameter method was used to simplify equivalently the rotor-blade system,then a lumped parameter model of the system torsional vibration was established.The torsional vibration model of the rotor-blade system with different crack parameters was established.The torsional vibration response of the rotor-blade system under different blade crack parameters was analyzed,and it was found that if there are cracks in the blade,the first harmonic response of the shaft system torsional vibration increases.Then the influences of crack depths and positions on the torsional vibration response of the system was discussed.Based on the experimental bench,the torsional vibration response of the system was tested by replacing the blades with cracks of different positions and depths.Then it was obtained that the torsional vibration response of the system with cracked blades increases significantly at the first harmonic compared to intact blade systems,and the calculation model and results were verified.The use of torsional vibration to diagnose blade crack faults proposed in this paper is of reference value to engineering.