Analytical and experimental investigation of the existence of simultaneous forward and backward whirling motion of Jeffcot rotor supported on hydrodynamic bearings

Whirling motion of Jeffcot Rotor supported on two identical hydrodynamic bearing is taken as a basis for this study. Effect of flexibility and load parameter on the occurrence of backward whirl between critical speeds is studied. As the disk whirls in the backward sense in between the critical speeds, the journal continues to whirl in the forward sense. The present investigation reveals that the backward whirl commences at the disk and as the speed increases, it extends over a certain central portion of the shaft and then shrinks back towards the disk before disappearing.;In actual practice the manufacturing precision difficulties and wear does introduce dissimilarity in the supportive bearings. The response analysis of the rotor supported on the dissimilar bearings is analyzed analytically. Effect of dissimilarity of the bearings on the pattern and occurrence of forward and backward whirling motion is studied.;Experimental verification of the simultaneous forward and backward whirl motion is carried out on a laboratory model of a simple Jeffcot rotor mounted on identical journal bearings. Instrumentation involving proximity pickups, oscillator, amplifiers, demodulator are used to provide an output voltage signal proportional to the displacement. A differentiator--multiplier--filter circuits is designed and built to identify the sense of the whirling motion with the input voltage signal from the demodulator. The phenomenon of the existence of forward and backward whirling motions at the bearing and at the rotor disk is established through experimental measurements. (Abstract shortened by UMI.)...