Rolling Stream Trails: An Alternative Cavitation Analysis

Abstract

The rolling stream trail (RST) model introduces a new formulation of cavitation analysis of an eccentric journal bearing; it is presented as a preferred foundation for cavitation analysis of a journal bearing to replace Floberg’s streamer hypothesis that had been adopted by many investigators in recent past. Based on a careful reinterpretation of published experimental photographic data, noting the blunt-nosed shape of the interspersing space that separates adjacent wetting outlines at the rupture boundary, it stipulates a 3D flow structure for transition from the filled fluid film (FFF) to a cross-void fluid transportation process. The transition starts as a two-component composite rupture front and becomes an adhered film (AF) that is masked by rolled-on stream trails, which are drawn from the rupture front. The AF moves with the journal surface across the void to feed the FFF at the formation boundary. Upon averaged across a full period of the rupture front, Olsson’s equation for flow continuity relative to a moving cavitation boundary yields a moving speed of the rupture front that is proportional to the reciprocal of the width fraction of the wet pockets multiplied into the FFF pressure gradient. For all nonvanishing width fraction of the wet pockets, both rupture and formation boundaries move with finite speeds. RST is an initial value time-dependent problem that deals with both the FFF and AF that are joined at rupture and formation boundaries. The initial fluid content in the void span is bracketed between a dry void and a freshly cavitated wet void. As time progresses, transportation of AF across the void space and boundary motions form a coupled evolution process. Formulas for the boundary motions indicate that the formation boundary would become stationary simultaneously as the rupture boundary approaches the Swift–Stieber condition. For implementation of RST analysis, analytic functions originally derived by Sommerfeld in his classical paper are employed to construct FFF pressure profile and subsequently to calculate boundary speeds. Precision and robustness achieved in this approach assure viability of RST cavitation analysis. Results include temporal evolution profiles of the FFF pressure and the cavitation boundary trajectories. Basic concepts and mathematical formulation of RST are applicable to 2D problems. A scheme to include squeeze film motion is outlined.