Application of Liquid Coating to a High-speed Moving Surface

应用于铁路轨道的液体摩擦改进剂（LFM）将车轮和轨道之间通常较高的摩擦系数降低到适度水平。适度的摩擦力对于爬坡和制动是足够的，但与上级燃料经济性和减少的履带磨损和噪音相关。改进LFM的应用方式将降低系统维护成本，并导致每年数千万美元的燃料节省和相应的温室气体减少。虽然这里提出的研究是出于LFM应用到轨道的具体技术问题，它是一个基本的字符，可能会有显着的影响，在其他应用领域，如油漆涂层和液体冲击冷却。LFM可以应用的一种方式是通过将LFM的非雾化的自由表面射流从列车引导到轨道上。在接近冲击点处，射流径向扩散，就像射流冲击在静止表面上一样，形成薄的薄片。在离冲击点稍远的地方，射流仍保持在表面上，粘性效应导致射流流体向下游对流，形成整体U形薄片结构。将使用先进的实验技术（PIV和LIF）研究撞击过程的流体力学。将根据边界层理论结合自由表面模型，建立薄板的分析模型。LFM液体是非牛顿的，该理论将扩展到非牛顿冲击的情况下，并预测射流飞溅的发生。 将线性调频应用于轮轨界面的第二种方法是将其从固定位置渗出到轨道上，当火车经过时，它被车轮拾取。当正确操作时，每个车轮都在LFM的薄润滑层上行驶。我们已经开始通过实验和分析技术的结合来研究这种涂层过程。我们已经建立了一个1/5比例版本的机车车轮。我们添加微量的染料的线性调频和使用激光诱导荧光推断润滑层的厚度。我们将用高速成像来增强这些测量，以可视化辊隙下游的膜分裂。我们目前的理论假定，车轮和轨道之间的流动近似是二维的，并由雷诺润滑理论。该理论已被开发为牛顿流体，我们将修改该理论，考虑假塑性和弹性行为的真实的线性调频。我们将比较扩展的理论和实验测量的薄膜厚度时，车轮滚过池的假塑性流体或弹性流体。润滑膜中的压力很高。我们将研究是否有一个顺应性的车轮，在这种压力下变形，增加线性调频传输。在某些运行条件下，车轮和钢轨之间不会形成润滑层。我们将通过实验和分析来探讨这种润滑失效。

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.