Discussion of "a Review of the Rotordynamic Thermally Induced Synchronous Instability (Morton) Effect" (Tong, X., Palazzolo, A., and Suh, J., 2017, ASME Appl. Mech. Rev., 69(6), p. 060801)

The authors present a timely review of rotor thermal bending and its potential instability through the Morton effect, which is associated with hydrodynamic fluid film journal bearings. They describe the viscous shearing origin of the heat source and its symptoms through to the rotor dynamics. There then follows an overview of the modeling approaches to predict the coupled fluid-thermal-rotor dynamics and their stability/instability. These are related to the prediction of high and hot spots and their phase difference. Experimental methods are then covered followed by parameter influences and options to avoid the Morton effect, some of which may conflict with the original rotor dynamic design specification. In some cases the sensitivity of the parameter variations may be significant. This discussion article will consider some of the questions on the predictive capabilities for the Morton effect. The inherent asymmetric shaft heating mechanism that drives rotor thermal bending is also related to other phenomena in other rotating machines and systems.