# Experimental Study on Horizontal Pipeline Transportation Characteristics of Coarse Particle
## 4 Results and Discussion
### Heterogeneous flow suspension motion  
Figure 11a-c show schematic diagrams of the velocity distribution extraction process for three different particle sizes exhibiting heterogeneous flow suspension motion. In this flow pattern, the upper section of the pipeline is primarily characterized by suspended motion, with coarse particles almost filling the entire pipeline. The maximum particle velocity remains concentrated near the centerline of the pipeline, and the velocity distribu  
Figure 9: Sedimentary bed type with jumping and rolling particles (**a**) d = 0.9 mm; (**b**) d = 1.5 mm; (**c**) d = 2.5 mm (The red dashed line in the first three pairs of figures shows the location of the cross-section selection. The red and green lines are the direction of the velocity obtained by the PIV technique processing. The axis y represents the ratio of the actual height of the vertical direction of the pipe to the diameter of the pipe, which will not be repeated later).  
tion characteristics are similar to those observed in the bed type of translational motion. However, with an increase in velocity, the proportion of coarse particles also increases, causing the high-speed particle region near the centerline to expand, resulting in a higher overall flow velocity. The highest particle velocity is observed in the central area of the pipeline, while the velocity of the coarse particles in the upper and lower halves of the pipeline gradually decreases as the distance from the centerline increases.  
By comprehensively comparing the characteristics of the three types of coarse particle flow patterns mentioned above, the reasons for their occurrence are analyzed from the perspectives of particle forces, collisions, and the influence of water flow on the coarse particles.  
Influence of the boundary layer near the pipe wall: the logarithmic velocity distribution of coarse particles is primarily influenced by the boundary layer near the pipe wall. Fluid molecules in this boundary layer are affected by the wall, and coarse particles, driven by the inertia of the water flow, tend to align with the velocity distribution characteristics of the water. Simultaneously, the peak particle velocity is slightly shifted downward due to the influence of the particles' own weight.  
The balance between the lifting force provided by the water flow and the gravity of the particles plays a crucial role in determining particle behavior: the direction of the drag force exerted by the water flow on coarse particles is relatively random. As the water flow speed increases and the drag force becomes stronger, coarse particles are more likely to be lifted by the water flow, leading to a more even dispersion of particles throughout the pipe. This reduction in collision and friction allows coarse particles to more easily suspend or move.  
The degree of collision and friction between coarse particles varies across different flow patterns: in the sedimentation bed flow pattern, the collision and friction between particles are at their highest, which weakens the influence of the water flow drag force and facilitates  
Figure 10: Moving movement (**a**) d = 0.9 mm; (**b**) d = 1.5 mm; (**c**) d = 2.5 mm.  
particle settling. In contrast, suspended coarse particles are less affected by particle collision friction and only need to maintain a balance between their own gravity and the upward force created by the water flow drag force in order to sustain their motion state.