Author(s): Yushu Xie; Bruce W. Melville
Linked Author(s): Bruce W. Melville
Keywords: Coarse particle entrainment; Instrumented sensors; Particle tracking velocimetry; Bed packing; Threshold velocity
Abstract: This study investigates the entrainment mechanics of a protruding coarse particle over a regularly roughened bed. A series of laboratory experiments were conducted to explore the effect of various flow depths and bed arrangements on the particle entrainment movement. The coarse particle is instrumented with a tri-axis accelerometer, enabling the measurement of its acceleration during dislodgement. Simultaneously, Particle Tracking Velocimetry (PTV) technique is employed to capture the flow field around the coarse particle. Acceleration data reveals imperceptible movements of the coarse particle after its dislodgement (as depicted in the figure). The experimental findings indicate that bed packing significantly affects the particle’s entrainment threshold and the path of movement. In certain scenarios, lateral movement predominates due to the entrainment path being determined by the least work done by the flow, even if the movement direction is not aligned with the flow. The presence of the coarse particle substantially changed the spatial distributions of time-averaged velocities, turbulent kinetic energy, and Reynolds shear stress, when compared to those obtained from a flat rough bed (Xie et al., 2022). Thus, the double-averaged flow velocity at a distance of 2D (D is the diameter of the coarse particle) upstream the particle center is selected to represent the approach flow velocity. The mean threshold velocity and resultant impulse show consistent dependence on the bed arrangement. In general, using the instrumented particle shows a good prospect of studying particle movement mechanisms. This study acknowledges certain limitations and briefly discusses potential applications for future research.
Year: 2024