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中国物理学会期刊

转鼓中颗粒流动的迟滞-连续流转变

Continuous-Flow Transition in Granular Flow within a Rotating Drum

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  • 颗粒物质的流态转变是非平衡统计物理与颗粒物理的重要研究问题,并与滑坡、雪崩、泥石流等灾害过程紧密相关。尤其是颗粒堆积由间歇性崩塌向连续稳定流动的转变,是多类地质灾害的触发与演化关键环节。尽管已有研究表明转变点受粒径、摩擦、形状与边界条件等多因素控制,但颗粒材料弹性模量对转变点的调制作用仍缺乏系统研究。本文结合转鼓实验和与之匹配的数值模拟,通过改变颗粒半径和颗粒材料模量,研究单分散体系在转鼓中的迟滞到稳流的转变。通过调节转鼓角速度,借助高速摄影与图像处理得到堆积表面倾角等动力学量。通过引入由于材料模量不同而导致的无量纲变形量,提出了包含模量影响的修正弗劳德数Fr**。结果表明,对于不同粒径与不同模量体系,其转变点可由修正后的弗劳德数实现统一,即当Fr**Frc** 时不同模量的颗粒系统由迟滞态转变为稳流态。该结果为建立统一的临界条件预测框架提供依据,并有助于提升相关灾害阈值预测的可操作性,同时为颗粒介质非平衡流变与本构理解提供实验支撑。

    Flow-state transitions in granular materials constitute an important problem in nonequilibrium statistical physics and granular physics, and are closely related to geophysical hazards such as landslides, snow avalanches, and debris flows. In particular, the transition of a granular pile from intermittent collapse to continuous steady flow is widely regarded as a key step in the initiation and evolution of many natural hazards. Although previous studies have shown that this transition is governed by factors such as particle size, friction, shape, and boundary conditions, the role of particle elastic modulus in modulating the transition threshold remains insufficiently understood.In this work, we combine rotating-drum experiments with matched numerical simulations to systematically investigate the transition from a hysteretic state to steady flow in monodisperse granular systems by varying particle radius and material elastic modulus. By tuning the drum rotation rate and employing high-speed imaging together with image-processing techniques, we extract key dynamical quantities such as the free-surface inclination angle. Based on these measurements, we introduce a dimensionless deformation parameter associated with differences in material modulus, and further propose a modified Froude number, denoted as Fr**, that explicitly incorporates elastic-modulus effects.Our results show that, for systems with different particle sizes and elastic moduli, the transition thresholds are significantly scattered when expressed in terms of the conventional Froude number. In contrast, when recast in terms of the modified Froude number Fr**, these thresholds collapse onto a unified criterion. In other words, the transition from the hysteretic regime to continuous steady flow can be described by a single dimensionless parameter that simultaneously accounts for inertia, gravity, and elastic deformation.These findings demonstrate that particle elasticity plays a systematic and quantifiable role in granular flow-state transitions. The proposed modified criterion provides a foundation for establishing a unified predictive framework for critical conditions, improves the practical applicability of hazard-threshold estimation, and offers experimental support for understanding the nonequilibrium rheology and constitutive behavior of granular media.

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