Author(s): Yasuo Hattori; Hitoshi Suto; Keisuke Nakao; Kiyoshi Toshida; Mitsuharu Nomura
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Keywords: Deposition; Lab test; Shadow imaging technique; Terminal velocity; Turbulence
Abstract: We experimentally investigated dynamics of sand-silica particles in an upward air field, which mimics sedimentation of the particles in a river flow, especially paying attention to interactions between the dynamics and fluctuating velocities (turbulences) accompanied with the upward flow. The velocity of upward flow was set to the terminal velocities of the particles in air flows. A vertical wind-tunnel with an active grid was used to generate upward flows with turbulences. Size, shape and movement of particles seeded in a test section were measured by a shadowgraph technique; the particles were illuminated by high-intensity pulsed lasers, Nd: YAG laser, with an optical diffuser, and were captured by a CCD camera with a long-distance microscope lens, which was placed in front of the light source. After confirming that the experimental set-up has a capability to capture the movement and shape of particles, i.e., measured settling velocities without upward flows agree well with terminal velocities estimated by empirical formula proposed in previous studies, we revealed that the typical characteristics for dynamics of non-spherical particles in the upward flows with turbulences. The particles mainly choose two orientations, vertical and horizontal orientations in the flow, causing the scatter of terminal velocities. Also, the turbulences in the upward flows drastically decrease the terminal velocities with changes in the orientation of particles.
Year: 2020