Complex fluid instabilities and flow patterns in shear thickening fluids

剪切增稠流体中复杂的流体不稳定性和流动模式

• 批准号: 2442209
• 金额: --
• 依托单位: Swansea University
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2020
• 资助国家: 英国
• 起止时间: 2020 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2442209
• 关键词: Complex; fluid; instabilities; flow; patterns

Shear thickening fluids display an increase in viscosity with applied stress. In the extreme, the suspension viscosity increases by orders of magnitude, and the material goes from liquid-like to solid-like (Discontinuous Shear Thickening, DST). Shear thickening, and DST in particular, has for decades been an intractable problem in the field of complex fluids and rheology. However, recent breakthroughs have generated much excitement and scientific debate as to the origins of DST, now explained as a transition from lubricated to frictional particle contacts in response to increased stress. This project will study complex flow patterning and fluid instabilities involving discontinuous shear thickening fluids and relate the observable dynamics to the new theoretical models. The proposed PhD project is inspired by preliminary observations of novel flow instabilities caused by the shear thickening behaviour of corn starch suspensions. Specifically, the project objectives are to study 1) The formation of roll waves during film flow of shear thickening fluids down inclined surfaces, 2) The free-fall Plateau-Rayleigh instability in liquid jets of DST materials, and 3) The potential formation of density waves travelling against the flow direction (analogous to traffic jam shock waves). The primary experimental variables include suspension density (Objectives 1,2,3), angle of gravity (Objectives 1,3), film thickness (Objectives 1,3), aperture diameter of liquid stream (Objective 2) and imposed pressure (Objective 2). Observables include wavelength, amplitude, space-time diagrams, wave velocities, liquid stream "precession" and droplet formation dynamics. In parallel with the experimental agenda, we will develop a new simulation code based on the Smoothed Particle Hydrodynamics (SPH) method in close collaboration with Prof. Ellero at the Basque Center for Applied Mathematics in Spain. The simulation code will be benchmarked against the rich experimental results described above, in addition to standard parallel plate rheological measurements.The overarching aim of the project is to reveal how the interparticle interactions give rise to DST behaviour which in turn give rise to complex flow dynamics. The project results will contribute to a deeper understanding of how complex flow patterns emerge in shear thickening fluid flows, which will allow optimisation of processing in the food and pharmaceutical sectors.

剪切增厚流体显示出粘度的增加，并具有施加的应力。在极端情况下，悬浮粘度通过数量级增加，材料从液体样到固体状（不连续的剪切增厚，DST）。数十年来，剪切增厚，尤其是DST在复杂的流体和流变学领域一直是一个棘手的问题。但是，最近的突破引起了关于DST的起源的激动和科学辩论，现在被解释为从润滑到摩擦颗粒接触的过渡，响应增加的压力。该项目将研究复杂的流动模式和流体不稳定性，涉及不连续的剪切增厚流体，并将可观察到的动态与新的理论模型联系起来。拟议的博士学位项目的灵感来自于玉米淀粉悬浮液的剪切增厚行为引起的新型流动不稳定性的初步观察。具体而言，项目目标是研究1）在倾斜表面的剪切增厚流体的薄膜流动过程中的形成，2）自由落体的高原rayleigh不稳定在DST材料的液体喷射液中，以及3）密度波的潜在形成（类似于流量的jam冲击波）。主要的实验变量包括悬架密度（目标1,2,3），重力角（目标1,3），膜厚度（目标1,3），液体流的孔径直径（物镜2）和施加的压力（目标2）。可观察到的包括波长，幅度，时空图，波速，液体流“进动”和液滴形成动力学。与实验议程并联，我们将基于平滑的粒子流体动力学（SPH）方法开发新的仿真代码，与西班牙巴斯克应用数学中心的Ellero密切合作。除了标准平行板流变学测量外，还将根据上述丰富的实验结果进行基准测试。项目的总体目的是揭示粒子间相互作用如何引起DST行为，从而产生复杂的流动动力学。该项目的结果将有助于更深入地了解剪切增厚流体流中的复杂流动模式如何出现，这将允许在食品和药物领域优化加工。