Cejas Cesare M, Wei Yuli, Barrois Remi, Frétigny Christian, Durian Douglas J, Dreyfus Rémi
Complex Assemblies of Soft Matter, CNRS-Solvay-UPenn UMI 3254, Bristol, Pennsylvania 19007-3624, USA.
Complex Assemblies of Soft Matter, CNRS-Solvay-UPenn UMI 3254, Bristol, Pennsylvania 19007-3624, USA and Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6396, USA.
Phys Rev E Stat Nonlin Soft Matter Phys. 2014 Oct;90(4):042205. doi: 10.1103/PhysRevE.90.042205. Epub 2014 Oct 21.
We investigate the formation of fingered flow in dry granular media under simulated rainfall using a quasi-two-dimensional experimental setup composed of a random close packing of monodisperse glass beads. Using controlled experiments, we analyze the finger instabilities that develop from the wetting front as a function of fundamental granular (particle size) and fluid properties (rainfall, viscosity). These finger instabilities act as precursors for water channels, which serve as outlets for water drainage. We look into the characteristics of the homogeneous wetting front and channel size as well as estimate relevant time scales involved in the instability formation and the velocity of the channel fingertip. We compare our experimental results with that of the well-known prediction developed by Parlange and Hill [D. E. Hill and J. Y. Parlange, Soil Sci. Soc. Am. Proc. 36, 697 (1972)]. This model is based on linear stability analysis of the growth of perturbations arising at the interface between two immiscible fluids. Results show that, in terms of morphology, experiments agree with the proposed model. However, in terms of kinetics we nevertheless account for another term that describes the homogenization of the wetting front. This result shows that the manner we introduce the fluid to a porous medium can also influence the formation of finger instabilities. The results also help us to calculate the ideal flow rate needed for homogeneous distribution of water in the soil and minimization of runoff, given the grain size, fluid density, and fluid viscosity. This could have applications in optimizing use of irrigation water.
我们使用由单分散玻璃珠随机紧密堆积组成的准二维实验装置，研究了模拟降雨条件下干燥颗粒介质中指状流的形成。通过控制实验，我们分析了从湿润前沿发展而来的指状不稳定性，它是基本颗粒（粒径）和流体性质（降雨量、粘度）的函数。这些指状不稳定性是水道的先兆，水道是排水的出口。我们研究了均匀湿润前沿和水道尺寸的特征，并估计了不稳定性形成过程中涉及的相关时间尺度以及水道指尖的速度。我们将实验结果与Parlange和Hill [D. E. Hill和J. Y. Parlange，Soil Sci. Soc. Am. Proc. 36, 697 (1972)] 提出的著名预测结果进行了比较。该模型基于对两种不混溶流体界面处扰动增长的线性稳定性分析。结果表明，在形态方面，实验与所提出的模型一致。然而，在动力学方面，我们考虑了另一个描述湿润前沿均匀化的项。这一结果表明，我们将流体引入多孔介质的方式也会影响指状不稳定性的形成。这些结果还帮助我们在已知颗粒大小、流体密度和流体粘度的情况下，计算土壤中水均匀分布所需的理想流速以及使径流最小化。这在优化灌溉用水的使用方面可能具有应用价值。
