## 3 Result and Analysis  
### Longitudinal Flow Characteristics  
To avoid the shelter from the adjacent sections, the odd and even sections were respectively plotted in two figures (see Figure 4).  
* Velocity distribution: The high-velocity flow from the inlet opening striking on the flow adjustment board caused the extremely high velocity \(u\) in the lower part of the FAA. Additionally, the high-velocity flow also caused the velocity \(v\)-\(w\) in the FAA to be in disorder, i.e., there are many differences in the magnitude and direction of flow velocity at different measurement locations in the FAA, and swirling flows were formed, which would affect the structural safety of the tank. Sections 3 and 4 were at the two sides of the flow adjustment board. In Section 3, the direction of the velocity \(v\)-\(w\) was mainly upward. Section 4 showed a more uniform velocity \(u\), and the velocity \(v\)-\(w\) was downward. The discharge capacity of the upper part of the flow adjustment board with bigger holes was higher than that of the bottom with smaller holes, so the water flowed into the SSA through the upper part of the board, which indicated that the flow adjustment board could redistribute flow with a high velocity from the inlet. The velocity \(u\) in the upper SSA was uniform with a range of \(-\)0.005-0.01 m/s (when the direction of the velocity vector component consistent with the positive direction of the corresponding coordinate axis, the velocity value was positive, and vice versa). The velocity \(v\)-\(w\) was lower than that in the FAA, and it only increased at the rear of the SSA due to the resistance of the baffle, and the uniform velocity was beneficial to the large particles settling in the SSA. The flow velocity in the upper part of the ISA increased compared with that in the SSA (see Figure 4a).
* Longitudinal dimensionless turbulence intensity (\(I_{X}\)) distribution: The \(I_{X}\) was high in the FAA and SSA, while low in the ISA. The \(I_{X}\) was uneven in the FAA, which was mainly caused by the backflow caused by the water from the inlet that struck the flow adjustment board. When the water flowed through the board, the velocity would be intensely redistributed in a short time, leading to a violent turbulence of the flow with the \(I_{X}\) value within 16-24%. The turbulence helped to further dissipate the kinetic energy of the flow and decrease the velocity. In the latter half of the SSA, the \(I_{X}\) value gradually decreased to 2-8%, contributing to the adhesion of the viscous sediment particles to form the flocculation of sediment and to the flocs settling in the ISA. The \(I_{X}\) value in the upper part of the ISA was 0-4%. The flow in the inclined tubes was laminar, so the flow pattern was still stable after flowing out of the inclined tubes. The \(I_{X}\) of the latter part of the ISA increased affected by the overflow suction (see Figure 4b).
* Longitudinal dimensionless Reynold shear stress (\(R_{XZ}\)) distribution: This represents the dimensionless Reynolds shear stress in the direction \(X\) and normal to \(Z\). The distribution of the \(R_{xz}\) was high in the FAA and the SSA, and low in the upper part of the ISA with a range of 0-8% (see Figure 4c). The \(R_{XZ}\) in the FAA was in the range of 4-8%, and the maximum value appeared in the range of \(Z\) = 50-100 cm. The flocculation of sediment in the inclined-tube settling tank mainly appeared in the range of \(Z\) = 50-150 cm, so the moderately increased \(R_{XZ}\) could further promote the flocculation of sediment and accelerate its settling.