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Fingering instabilities in Newtonian and non-Newtonian fluids.

机译：牛顿流体和非牛顿流体中的指法不稳定性。

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摘要

Fingering has been studied in different fluid systems. Viscous fingering, which is driven by a difference in viscosity between fluids, has been studied by both experiments and numerical simulations. We used a single fluid with a temperature-dependent viscosity and studied the instability for a range of inlet pressures and viscosity ratios. The spreading and fingering of a fluid drop subjected to a centrifugal force, known as spin coating, has also been studied for a range of drop volumes and rotation speeds, both for a Newtonian and a non-Newtonian fluid.;The spreading of silicone oil, a Newtonian fluid, during spin coating follows the time dependence predicted theoretically, although with a shift in the scaled time variable. Once the radius of the spreading silicone oil drop becomes large enough, fingers form around the perimeter of the drop for all experimental conditions studied. The number of fingers and the growth rate of the fingers are in agreement with theoretical predictions. Fingers are also observed to form for high enough drop volumes and rotation speeds during the spinning of a non-Newtonian fluid drop, Carbopol, which possesses a yield stress. In this case the fingering is a localized effect, occuring once the stress on the drop exceeds the yield stress, rather than the result of an instability as in the Newtonian case.;Experiments on viscous fingering with a single fluid, glycerine, show that an instability occurs at the boundary separating hot and cold fluid. The results indicate that the instability is similar to that which occurs between two miscible fluids. Fingering only occurs for high enough values of the inlet pressure and viscosity ratio. The wavelength of the fingering pattern is found to be proportional to the cell width for the two smallest cell widths used. The fingering patterns seen in the simulations are very similar to the experimental patterns, although there are some quantitative differences. In particular, the wavelength of the instability is seen to depend only weakly on the cell width.
机译：已经在不同的流体系统中研究了指法。由流体之间的粘度差异驱动的粘性指法已通过实验和数值模拟进行了研究。我们使用一种粘度随温度变化的单一流体，并研究了一系列入口压力和粘度比的不稳定性。还对牛顿和非牛顿流体在一定范围内的液滴体积和旋转速度下，研究了受到离心力作用的液滴的散布和指状化（称为旋涂）。 ，即牛顿流体，在旋涂过程中遵循理论上预测的时间依赖性，尽管比例时间变量发生了变化。一旦散布的硅油滴的半径变得足够大，在所有研究的实验条件下，手指都会在滴的周围形成手指。手指的数量和手指的生长速度与理论预测一致。在具有屈服应力的非牛顿流体液滴Carbopol的旋转过程中，还观察到手指形成了足够高的液滴体积和旋转速度。在这种情况下，指法是一种局部效应，一旦液滴上的应力超过屈服应力，就会发生，而不是像牛顿法那样是不稳定性的结果。;使用单一液体甘油进行粘性指法的实验表明在将热流体和冷流体分开的边界处会出现不稳定性。结果表明，这种不稳定性类似于两种可混溶流体之间的不稳定性。仅当入口压力和粘度比值足够高时才出现指状现象。发现指状图案的波长与所使用的两个最小单元宽度的单元宽度成比例。在模拟中看到的指法模式与实验模式非常相似，尽管存在一些数量上的差异。尤其是，不稳定的波长仅弱地依赖于晶胞宽度。

著录项

  • 作者

    Kennedy, Kristi E.;

  • 作者单位

    Memorial University of Newfoundland (Canada).;

  • 授予单位 Memorial University of Newfoundland (Canada).;
  • 学科 Physics Fluid and Plasma.
  • 学位 Ph.D.
  • 年度 2007
  • 页码 163 p.
  • 总页数 163
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 普通生物学;
  • 关键词

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