A NUMERICAL AND EXPERIMENTAL INVESTIGATION OF TAYLOR FLOW INSTABILITIES IN NARROW GAPS AND THEIR RELATIONSHIP TO TURBULENT FLOW IN BEARINGS
The relationship between the onset of Taylor instability and appearance of what is commonly known as “turbulence” in narrow gaps between two cylinders is investigated. A question open to debate is whether the flow formations observed during Taylor instability regimes are, or are related to the actual “turbulence” as it is presently modeled in micro-scale clearance flows. This question is approached by considering the viscous fluid flow in narrow gaps between two cylinders with various eccentricity ratios. The computational engine is provided by CFD-ACE+, a commercial multi-physics software. The flow patterns, velocity profiles and torques on the outer cylinder are determined when the speed of the inner cylinder, clearance and eccentricity ratio are changed on a parametric basis. Calculations show that during the Taylor and wavy vortex regime velocity profiles in the radial direction are sinusoidal with pressure variations in the axial direction even for the case of the “long journal bearing” (L/D>2). Based on these findings, a new model for predicting the flow behavior in long and short journal bearing films in the transition regime is proposed. Unlike the modified turbulent viscosity of the most accepted models (Constantinescu, Ng-Pan, Hirs and Gross et al.), the viscosity used in the new model is kept at its laminar value. Experimental torque measurements and flow visualization are performed for three kinds of oils with different viscosities. It is shown that in general there is a good agreement between the numerical and experimental torques except those in turbulent regime. Comparison between numerical and experimental flow patterns is also made and it shows that they match well in the Couette, Taylor and Wavy regimes. In general there is a good agreement between the numerical and experimental results including torque measurements and flow patterns. The new model for predicting the flow behavior in journal bearing films in the transition regime is justified.
School:The University of Akron
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:taylor instability flow patterns velocity profiles new model transition narrow gaps long journal bearings reynolds equation turbulence models torque measurements visualizations
Date of Publication:01/01/2007