3.3.1. Particle Trajectory

– – Figure 10 shows the trajectory of the particle motion in the entire pipeline and Figure 11 shows the trajectory of particle hitting the wall of the elbow, where the color of the particles indicates the velocity. Form Figure 10a,b, particles in the first straight section basically maintained the same velocity, except for particles with the minimum speed near the extrados surface. In addition, at the junctions of elbow and the first straight section, the velocity of the solid particles was changed, and particles were significantly moved toward the extrados surface. From Figure 10c, the particles in the first half of the elbow hit the extrados surface along an approximately straight line, and particles near the extrados surface were gradually pushed toward intrados surface. As shown in Figure 10c–e, many particles hit the extrados surface of elbow. As shown in Figure 11, the particles hit the elbow forming a curved distribution and bouncing off the wall. A small quantity of particles lagged near the intrados when particles are at the junction of the elbow and the second straight section. In Figure 10f–h, the motion of the particles in the second straight section gradually became more dispersive, and the particles formed the cloud cluster.

**Figure 10.** Three-dimensional diagram of particle trajectories in the pipeline (the color indicates the speed). (**a**) t = 0.10 s particle trajectories; (**b**) t = 0.11 s particle trajectories; (**c**) t = 0.12 s particle trajectories; (**d**) t = 0.14 s particle trajectories; (**e**) t = 0.16 s particle trajectories; (**f**) t = 0.18 s particle trajectories; (**g**) t = 0.21 s particle trajectories; (**h**) t = 0.24 s particle trajectories.

**Figure 11.** The trajectory of particles hitting the wall (the color indicates the speed). (**a**) t = 0.10 s particle trajectories; (**b**) t = 0.11 s particle trajectories; (**c**) t = 0.12 s particle trajectories; (**d**) t = 0.13 s particle trajectories; (**e**) t = 0.14 s particle trajectories; (**f**) t = 0.15 s particle trajectories; (**g**) t = 0.16 s particle trajectories; (**h**) t = 0.17 s particle trajectories.
