The Study Of The Dynamic Characteristics Of A Mini Gas Turbine

A mini gas turbine's structure is complex, and it always suffers various of extreme forces, due to the higher speed of its rotors. Therefore, it is essential to analysis the dynamic characteristics of the rotors to ensure their normal operation under safe condition.The main work of the paper is finished by means of the finite element analysis software ANSYS. Firstly, the entire geometry model and finite element model are created in ANSYS. As so many types and numbers of the parts are involved, the paper discusses the modeling ideas, items of model simplification, and compares and analyzes the element types used in the model, according to the concrete characteristic of every part.The supporting system is used to position and support the rotors. So its vibration characteristic will significantly affect the rotor's dynamic characteristic. The paper calculates the static stiffness and dynamic stiffness of the supporting system's four bearing position, to obtain the supporting system's static displacement response under constant load, and dynamic displacement response under harmonic load.There are a compressor rotor and a turbine rotor in a gas turbine. And the turbine rotor researched in the paper has a simple and continuous structure. The first order critical speed values under different support stiffness are compared in the paper. The result shows that the first order critical speed of the turbine rotor decreases by 42.5% under both supporting system's static stiffness and bearings'support stiffness, and by 44.8% under both supporting system's static stiffness and bearing's support stiffness, compared with that under bearings'support stiffness only. The calculation on the turbine rotor's steady state unbalance response displays that the second turbine disk is the most susceptible one to the effect of unbalance mass. And the result also reveals that improving the distribution of unbalance mass, increasing bearing damping or reducing the total support stiffness can effectively lessen the turbine rotor's steady-state unbalance response displacement peak value.The compressor rotor is a rod fastening rotor, with 15KN's preload on every rod. In the paper, the compressor rotor is assumed as a continuous rotor, in order to facilitate the subsequent analysis and calculation. Under the assumption, both the lateral natural frequency and the first order critical speed of the compressor rotor decrease, with the increase of preload. The paper also calculates the first order critical speed of the compressor rotor under different support condition. The result shows that the first order critical speed of the compressor rotor decreases by 53.2% under both supporting system's static stiffness and bearings'support stiffness, and by 54.9% under both supporting system's static stiffness and bearing's support stiffness, compared with that under bearings'support stiffness only. The most susceptible disk to unbalance mass is the first stage one of the compressor rotor. And with the existence of the supporting system's static stiffness, the peak value of the steady-state displacement round the first order critical speed will decrease by 56.9%.