Vibration characteristics of a high-speed turbocharger rotor with mass unbalance based on simulation and experiment

Aiming at the problem of large-amplitude vibration appearing in turbochargers due to the effect of unbalance and nonlinear oil whirl/whip during operation, vibration characteristics with the variation of unbalance is studied by combining the simulation and the experimental test. Based on FE method and DOF reduction technique, a realistic turbocharging rotor is discretized into a series of master- and sub-elements by Timoshenko beam theory. The motion equations of turbocharger rotor-bearing system are derived by coupling rotor-floating ring equation and the oil-film Reynold equation. The research focuses on the unbalance effect on the sub-synchronous vibration and the total vibration level. The unbalance distribution, unbalance level, and the relative phase are the variables in the study. The result shows that 0.12× sub-synchronous from outer oil-film instability is responsible to the severe vibration at high-speed working conditions. Meaningfully, a suitable unbalance can significantly increase the onset speed for instability, and reduce overall vibration level. The mass unbalance of 1.5 g·mm on the compressor side shows good vibration characteristics, while the unbalance on the turbine side should be eliminated as much as possible. The proposed research provides a certain guidance for suppressing the total vibration level, and to control the unbalance in turbocharger rotor during operation.