The Morton effect is a rotordynamic phenomenon characterized by slowly diverging synchronous vibrations. The synchronous vibration vector describes a spiral with increasing amplitude. For long, this phenomenon was not correctly diagnosed because its time scale is order of magnitudes larger than the rotation frequency. It is now known that Morton effect appears due to the thermal unbalance created by the non-uniform heating of the journal guided by a lubricated bearing.

There are two category of methods for analyzing the Morton effect. The first is based on the power of numerical methods for integrating the transient, non-linear, coupled models of rotordynamic, thermoelasticity and lubricated journal bearing analyses. The time effort required for methods of this class depend on the accuracy of the employed models.

In the second category are simplified models. They are based on influence coefficients linking the three phenomenon concurring to the Morton effect: the total unbalance response of the rotor (A), the rotor surface temperature difference induced by synchronous vibrations (B) and the thermomechanical deformation of the rotor (C). Following the methods proposed in the literature, the three influence coefficients describing these phenomenon are estimated by using linear (small perturbations), decoupled (independent) models.

The present work retains the idea of using influence coefficients but different alternatives for estimating them are analyzed. The proposed models are more complex and accurate being based on the non-linear unbalance response (large amplitude vibrations), the non-isothermal flow in the journal bearing and 3D thermoelastic analyses of the rotor. The simplification comes from the uncoupled way of using the models.

The results are of the original simplified stability analysis and of the new modified one are compared with the experimental data obtained for a short (rigid) and a long (flexible) rotor guided by a ball bearing and a cylindrical journal bearing. Improvements obtained by using the modified simplified stability analysis are clearly underlined.


Stability Analysis of the Morton Effect of Rigid and Flexible Rotors

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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