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首页> 外文学位 >Topics in fluid mechanics: I. On the stability of stratified flows. II. Droplet-droplet and particle-plane interactions near contact.
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Topics in fluid mechanics: I. On the stability of stratified flows. II. Droplet-droplet and particle-plane interactions near contact.

机译：流体力学主题：I.关于分层流动的稳定性。二。液滴-液滴与粒子平面之间的相互作用接近。

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The first part of this dissertation examines the nature of interfacial instabilities between two stratified viscous fluids, particularly for unsteady, accelerating flows. Experiments performed with a vertical interface subject to oscillations of the bounding wall are found to agree well with linear stability theory. A cyclic, three-part mechanism for wave growth is identified, which may explain instabilities occurring in transient process flows. A basic state pressure fluctuation, created by faulty pump operation or other nonidealities, is explored as a possible instability mechanism in pressure driven channel flow. The linear theory reveals that growth rates of an interfacial disturbance can be strongly affected by a weak oscillation, provided that forcing is introduced at the correct, “natural” frequency. This selectivity with respect to frequency arises due to linear interactions between the interfacial disturbance and a secondary disturbance flow which travels upstream relative to the base flow or is contained within one of the two fluids. Finally, the stability of three experimental systems are reexamined through use of a weakly nonlinear simulation which includes all quadratic and cubic interactions between discrete Fourier modes. These calculations extend beyond the range of situations accessible by the popular Stuart-Landau theory, and resolve many discrepancies between observation and Orr-Sommerfeld predictions.; Part II of this dissertation considers experimentally two distinct problems in particulate flows. A dilute, stabilized emulsion in a simple bounded shear flow is visualized through optical techniques. The anisotropy of droplet-plane interactions causes drops to drift inward toward the centerline; a shear induced gradient diffusivity due to irreversible droplet-droplet interactions acts to disperse the drops. The balance of these two competing mechanisms provides a useful measure of the diffusivity of deformable particles. The second problem studied concerns the motion of a rigid, rough sphere under shear in contact with a plane. At small but finite Reynolds number, a translating and rotating sphere experiences an inertial lift force, which can overcome other forces acting on the sphere and remove the particle from the surface. It is demonstrated that the surface roughness has a profound effect on particle motion.
机译：本文的第一部分探讨了两种分层粘性流体之间的界面不稳定性的性质，特别是对于不稳定的加速流动。发现对垂直界面进行边界墙振动的实验与线性稳定性理论非常吻合。确定了波动的三部分循环机制，这可以解释瞬态过程流中发生的不稳定性。探索了由错误的泵操作或其他不理想因素引起的基本状态压力波动，它是压力驱动通道流动中可能的不稳定性机制。线性理论表明，如果以正确的“自然”频率引入强迫，则界面振动的增长率会受到微弱振荡的强烈影响。关于频率的这种选择性是由于界面扰动和相对于基本流向上游行进或包含在两种流体之一中的二次扰动流之间的线性相互作用而产生的。最后，通过使用弱非线性仿真来重新检查三个实验系统的稳定性，该仿真包括离散傅立叶模式之间的所有二次和三次相互作用。这些计算超出了流行的Stuart-Landau理论所能达到的范围，并解决了观测与Orr-Sommerfeld预测之间的许多差异。本文的第二部分在实验上考虑了颗粒流中两个不同的问题。通过光学技术可以观察到在简单的有限剪切流中的稀释，稳定的乳液。液滴平面相互作用的各向异性导致液滴向中心线向内漂移。由于不可逆的液滴-液滴相互作用而产生的剪切诱导梯度扩散率起到分散液滴的作用。这两种竞争机制的平衡为可变形颗粒的扩散性提供了有用的度量。研究的第二个问题涉及刚性，粗糙的球体在与平面接触的剪切作用下的运动。在较小但有限的雷诺数下，平移和旋转的球体会受到惯性升力，该惯性升力可以克服作用在球体上的其他力并将粒子从表面移除。结果表明，表面粗糙度对粒子运动有深远的影响。

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