Application of Liquid Coating to a High-speed Moving Surface

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Liquid friction modifier (LFM) applied to railroad tracks reduces the normally high coefficient of friction between the wheel and rail to a modest level. The modest friction is sufficient for hill climbing and braking, but is associated with superior fuel economy and reduced track wear and noise. Improving how LFM is applied would reduce the system maintenance cost and result in tens of millions of dollars of annual fuel savings and commensurate greenhouse gas reductions. Although the research proposed here is motivated by the specific technical problem of LFM application to tracks, it is of a fundamental character that could have significant impact in other application areas such as paint coating and liquid impingement cooling. One way that LFM can be applied is by directing a non-atomized, free-surface jet of LFM from the train onto the track. Close to the impingement point the jet spreads radially, like jet impingement on a stationary surface, forming a thin lamella. Somewhat further from the impingement point the jet remains on the surface and viscous effects cause the jet fluid to be convected downstream, forming an overall U-shaped lamella structure. The fluid mechanics of the impingement process will be studied using advanced experimental techniques (PIV and LIF). An analytical model for the lamella will be developed based on boundary layer theory combined with a model for the free surface. LFM liquids are non-Newtonian and the theory will be extended to the case of non-Newtonian impaction and to predict the onset of jet splash. A second way to apply LFM to the wheel-rail interface is to ooze it onto the track from a stationary location, where it is picked up by the wheels as the train passes. When done properly, each wheel rides on a thin lubrication layer of LFM. We have begun to study this coating process through a combination of experimental and analytical techniques. We have built a 1/5 scale version of a locomotive wheel. We add trace amounts of dye to the LFM and use laser-induced fluorescence to infer the lubrication layer thickness. We will augment these measurements with high speed imaging to visualize the film splitting downstream of the nip. Our current theory posits that the flow between the wheel and rail is approximately two-dimensional and is governed by Reynolds lubrication theory. The theory has been developed for Newtonian fluids and we will modify the theory to consider the pseudoplastic and elastic behaviour of real LFM. We will compare the extended theory to experimental measurements of film thickness when the wheel rolls over pools of a pseudoplastic fluid or an elastic fluid. The pressure in a lubricating film is very high. We will study whether having a compliant wheel that deforms in response to this pressure augments LFM transfer. For some operating conditions no lubrication layer forms between the wheel and rail. We will explore this lubrication failure experimentally and analytically.