Laboratoire FAST, Université Paris-Sud, CNRS, Université Paris-Saclay, F-91405, Orsay, France.
SPEC, CEA, CNRS, Université Paris-Saclay, F-91191 Gif-sur-Yvette, France.
Phys Rev E. 2017 Sep;96(3-1):032905. doi: 10.1103/PhysRevE.96.032905. Epub 2017 Sep 8.
We measure experimentally and analyze the resisting force exerted by a bidimensional packing of small disks on a larger intruder disk dragged horizontally at constant velocity V_{0}. Depending on the vibration level of the packing that leads to a granular "cold" or "hot" packing, two force regimes are observed. At low vibration level ("cold" granular medium), the drag force F does not depend on V_{0}, whereas for high vibrations ("hot" granular medium), the drag force increases linearly with V_{0}. Both regimes can be understood by the balance of two "granular temperatures" that can be defined in the system: a bulk temperature T_{b} imposed by the external vibration to the overall packing and a local temperature T_{0} induced by the own motion of the intruder disk in its vicinity. All experimental data obtained for different sizes and velocities of the intruder disk are shown to be governed by the temperature ratio T_{0}/T_{b}. A critical velocity V_{0c}, above which the system switches from "hot" to "cold," can be obtained in this frame. Finally, we discuss how these two "viscous" regimes should be followed by an inertial regime where the drag force F should increase as V_{0}^{2} at high enough velocity values, for V_{0} greater than a critical value V_{0i} corresponding to high enough Reynolds or Froude number.
我们通过实验测量和分析了二维小圆盘堆积体对水平拖动的大圆盘入侵者的阻力。根据堆积体的振动水平，即颗粒的“冷”或“热”堆积，观察到两种阻力区域。在低振动水平（“冷”颗粒介质）下，阻力 F 不依赖于 V_{0}，而在高振动水平（“热”颗粒介质）下，阻力 F 与 V_{0}呈线性增加。两种区域都可以通过两种“颗粒温度”的平衡来理解，这两种温度可以在系统中定义：由外部振动施加到整个堆积体的整体温度 T_{b}和由入侵者盘在其附近的自身运动引起的局部温度 T_{0}。所有对于不同尺寸和速度的入侵者盘的实验数据都表明，它们由温度比 T_{0}/T_{b}控制。在这个框架中，可以获得系统从“热”到“冷”切换的临界速度 V_{0c}。最后，我们讨论了这两种“粘性”区域应该如何被惯性区域跟随，在惯性区域中，当 V_{0}大于对应于足够高的雷诺数或弗劳德数的临界值 V_{0i}时，阻力 F 应该随着 V_{0}^{2}增加。
