Physics of Fluids, Universiteit Twente, P. O. Box 217, 7500AE Enschede, The Netherlands.
Forschungszentrum Jülich GmbH, Helmholtz-Institut Erlangen-Nürnberg für Erneuerbare Energien (IEK-11), Dynamik komplexer Fluide und Grenzflächen, Fürther Straße 248, 90429 Nürnberg, Germany.
Phys Rev E. 2018 Apr;97(4-1):042901. doi: 10.1103/PhysRevE.97.042901.
The behavior of a vertically vibrated granular bed is reminiscent of a liquid in that it exhibits many phenomena such as convection and Faraday-like surface waves. However, when the lateral dimensions of the bed are confined such that a quasi-one-dimensional geometry is formed, the only phenomena that remain are bouncing bed and the granular Leidenfrost effect. This permits the observation of the granular Leidenfrost state for a wide range of energy injection parameters and more specifically allows for a thorough characterization of the low-frequency oscillation (LFO) that is present in this state. In both experiments and particle simulations we determine the LFO frequency from the power spectral density of the center-of-mass signal of the grains, varying the amplitude and frequency of the driving, the particle diameter, and the number of layers in the system. We thus find that the LFO frequency (i) is inversely proportional to the fast inertial timescale and (ii) decorrelates with a typical decay time proportional to the slow dissipative timescale in the system. The latter is consistent with the view that the LFO is driven by the inherent noise that is present in the granular Leidenfrost state with a low number of particles.
垂直振动颗粒床的行为让人联想到液体，因为它表现出许多现象，如对流和类似法拉第的表面波。然而，当床的横向尺寸受到限制，形成准一维几何形状时，仅剩下反弹床和颗粒莱顿弗罗斯特效应。这使得可以观察到广泛的能量注入参数下的颗粒莱顿弗罗斯特状态，更具体地说，可以彻底表征该状态下存在的低频振荡（LFO）。在实验和颗粒模拟中，我们从颗粒质心信号的功率谱密度确定 LFO 频率，改变驱动的振幅和频率、颗粒直径以及系统中的层数。因此，我们发现 LFO 频率 (i) 与快速惯性时间尺度成反比，(ii) 与系统中与慢耗散时间尺度成正比的典型衰减时间解相关。这与 LFO 由颗粒莱顿弗罗斯特状态中存在的固有噪声驱动的观点一致，该噪声的颗粒数较少。
