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Dense granular flow around an immersed cylinder

机译：浸没圆柱体周围的密实颗粒流

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The flow around a fixed cylinder immersed in a uniform granular flow is studied experimentally. Experiments are performed in a tall vertical chute producing a quasi two-dimensional granular flow. A storage bin at the top of the chute feeds glass particles into the channel while the mean velocity of the flow is controlled by varying the exit width of a hopper located at the channel bottom. Measurements of the drag force acting on a fixed cylinder are made using a strain gauge force measurement system. The flow velocity field is measured through a transparent wall using a particle image velocimetry analysis of high speed video recordings of the flow. Experiments are performed for a range of upstream particle velocities, cylinder diameters, and two sizes of glass particles. For the range of velocities studied, the mean drag force acting on the cylinder is independent of the mean flow velocity, contrary to what is expected from any ordinary fluid. The drag force increases with cylinder diameter and decreases with particle diameter. The drag force scales with the asymptotic static stress state in a tall granular bed. The drag coefficient, defined in terms of a dynamic pressure and an effective cylinder diameter, scales with the flow Froude number based on the hydraulic diameter of the channel. This analysis indicates that the drag acting on the cylinder is strongly affected by the surrounding channel geometry. Although the drag force on the cylinder does not change with the upstream flow velocity, the flow streamlines do change with velocity. A large stagnation zone forms at the leading edge of the cylinder while at the trailing edge an empty wake is observed. The wake size increases with flow velocity. Measurements of the flow vorticity and granular temperature are also presented and discussed. (C) 2003 American Institute of Physics. [References: 25]
机译：实验研究了浸没在均匀颗粒流中的固定圆柱体周围的流动。在一个高的垂直滑槽中进行实验，产生近似二维的颗粒流。斜槽顶部的储物箱将玻璃颗粒送入通道，同时通过改变位于通道底部的料斗的出口宽度来控制平均流速。使用应变仪力测量系统对作用在固定气缸上的阻力进行测量。使用对流的高速视频记录进行粒子图像测速分析，通过透明壁测量流速场。对一系列上游颗粒速度，圆柱直径和两种尺寸的玻璃颗粒进行了实验。对于研究的速度范围，作用在气缸上的平均阻力与平均流速无关，这与任何普通流体所期望的相反。阻力随圆柱直径而增加，而随粒径减小。阻力在高颗粒床中随渐近静态应力状态而变化。根据动压和有效缸径定义的阻力系数，根据通道的液压直径与流量弗洛德数成比例。该分析表明，作用在圆柱体上的阻力受到周围通道几何形状的强烈影响。尽管作用在气缸上的阻力不随上游流速而变化，但流线确实随速度而变化。在圆柱体的前缘形成一个大的停滞区，而在后缘形成一个空的尾流。尾流尺寸随流速增加。还介绍和讨论了流动涡度和颗粒温度的测量方法。 （C）2003美国物理研究所。 [参考：25]

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