Flexible rotor balancing without trial runs using experimentally tuned FE based rotor model

A method based on experimentally calibrated rotor model is proposed in this work for unbalance identification of flexible rotors without trial runs. Influence coefficient balancing method especially when applied to flexible rotors is disadvantaged by its low efficiency and lengthy procedure, whilst the proposed method has the advantage of being efficient, applicable to multi-operating spin speeds and do not need trial runs. An accurate model for the rotor and its supports based on rotordynamics and finite elements analysis combined with experimental modal analysis, is produced to identify the unbalance distribution on the rotor. To create digital model of the rotor, frequency response functions (FRFs) are determined from excitation and response data, and then modal parameters (natural frequencies and mode shapes) are extracted and compared with experimental analogies. Unbalance response is measured traditionally on rotor supports, in this work the response measured from rotating disks instead. The obtained results show that the proposed approach provides an effective alternative in rotor balancing. Increasing the number of balancing disks on balancing quality is investigated as well.

Stability Analysis of the Morton Effect of Rigid and Flexible Rotors

This paper presents a stability analysis of the Morton effect. The analysis is an extension of the Murphy and Lorenz method [11] and is based on better estimates of three influence coefficients linking the phenomena contributing to the Morton effect: the total response to the rotor unbalance, the temperature difference on the rotor surface induced by synchronous vibrations and the thermomechanical deformation of the rotor. The models used in the present work are more complex and accurate because they are based on the non-linear unbalance response (large amplitude vibrations) of the rotor, on the non-isothermal analysis of the journal bearing flow and on a three-dimensional thermos-elastic analysis of the rotor. The results obtained with the original stability analysis of Murphy and Lorenz and with the modified one are compared with original experimental data obtained for a short (rigid) and long (flexible) rotor guided by a ball bearing and by a cylindrical bearing and presented in a previous work [20]. Both methods confirm the experimental results obtained for a short (rigid) rotor. They show that this rotor is not subject to instabilities generated by the Morton effect. However, the results obtained for a long (flexible) rotor are different. The simplified method of Murphy and Lorenz shows a stable behavior while the modified method presented in this work confirms the findings of [20] and indicates that the rotor could be subject to a Morton effect at rotational speeds close to the experimental conditions. The improvements obtained by using the modified stability analysis are therefore clearly underlined, as well as its inherent limitations.