Numerical simulation and nonlinear stability analysis of Francis Hydraulic Turbine-Seal system

Hydraulic and electromagnetic forces are main causes of vibrations in a hydraulic generating set. the unbalanced magnetic pull (ump) and nonlinear sealing force can produce large oscillations which will be dangerous to the shaft system. in the present paper,the kinetic model of a simplified unit shaft system,which mainly considers 6 degrees of freedom of rotor and turbine,under ump,and muszynska nonlinear sealing force is established. on this basis,the nonlinear stability of francis turbine-seal system is emphasized,and the effect of the seal parameters on system stability is also discussed,according to the lyapunov first approximation theory. the results show that there is very little likelihood of rub-impact phenomenon occurrence between the turbine and seal structure with nonlinear sealing force,if no other external interferences are taken into account. in addition,some suggestions about reducing self-excited vibration by parameters sensitivity analysis are given,which can be beneficial to the safety operation and vibration fault diagnosis for the units. © 2015 jordan journal of mechanical and industrial engineering.