Research on vibration induced by the coupled heat and force due to rotor-to-stator rub

Abstract

The paper sets up a set of coupled nonlinear differential equations with time variable coefficients to research the vibration of rotating machinery under rotor to stator rub condition. The seal stiffness, which is used to calculate rotor-stator contact force and rotor surface temperature distribution, is calculated using the finite element method firstly. Then, the transient heat conduction equations and rotor dynamic equations are combined together considering the thermal bending as unbalance fore acting on the rotor. The feedback from rub to vibration, asymmetric heat and shaft bending is analyzed by transient integration. The paper gives a detailed temperature distribution, thermal bending and vibration characteristics under different rotating speeds and rub conditions. It is found that rub-induced vibration tends to grow with time when the rotor is running below its critical speed. Rub section temperature difference grows quickly. Partial rub finally turns to full annular rub. Rub-induced vibration will be spiral and oscillation versus time if the rotor runs above the critical speed in the case of light rub. At severe rub, the vibration will be aggravated despite the rotor running above or under the critical speed. Two rub-induced vibration examples showing the coupled heat and force impact symptoms occurring in real turbines are given. Abnormal vibration phenomenon is analyzed and explained using the model.

Keywords

Rotating machinery rub thermal bending vibration

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