## 4 Results and Discussion
### Effect of the WSM on the Flow Distribution
#### 4.1.1 Flow Distribution When the Rake Is Not Operational
The initial decrease in the flow velocity is due to the drag provided by the bars, whereas the subsequent increase in the flow velocity is due to the decrease in the cross-sectional area of the flow. As the flow moves ahead from the bars of the sub-screen, the flow velocity is again decreased because of an increase in the flow's cross-sectional area. This decrease in the flow velocity is maintained in the space between the sub-screen and the main screen due to the drag provided by the main screen. As the fluid passes the main screen, a trend that is similar to that in the vicinity of the sub-screen is observed at a lower flow intensity due to the overall drag provided by the sub-screen. The flow treatment for the partially lowered configuration of the WSM is highlighted in Figure 6b. For the sub-screen in the partially lowered configuration, a trend that is similar to that for the sub-screen in the fully lowered configuration is observed. However, for the main screen in the partially lowered configuration, such an effect is negligible due to the drag caused by the sub-screen being slid in front of the main screen. The effect of the inlet velocity on the flow distribution in the upstream and downstream regions inside the sewage channel are investigated in Figure 8a-d, which provide insights into the loading conditions on various WTP components in the vicinity of the WSM. Figure 8a shows the velocity in the region that is upstream of the WSM when the sub-screen is fully lowered. We note that at this location in the channel near the floor, the flow velocity is slightly below the inlet velocity, and as we move up the channel height, this velocity approaches the inlet velocity. However, in Figure 8b, which shows the velocity upstream of the WSM when the sub-screen is partially lowered, we note that the channel opening overcomes the flow resistance caused by the channel floor. This means that when the channel is partially lowered, there is a fully open passage at the bottom, which, according to the continuity equation (where a smaller flow cross-sectional area leads to a higher velocity), results in increased velocity near the channel floor, which counteracts the drag caused by the channel floor. Figure 8c represents the downstream velocity when the sub-screen is fully lowered. We note in Figure 8c that when the sub-screen is fully lowered, there is a slight decrease in velocity compared to the upstream case in Figure 8a. This reduction is due to the resistance introduced by the WSM as water flows through it. As we move upwards from the channel floor in Figure 8c, the flow initially increases slightly because resistance at the floor decreases as we move upward. However, when the sub-screen and main screen overlap at a certain height, they create significant resistance, leading to a temporary decrease in velocity in that region. Beyond this overlap region, where only the main screen is present, the flow speed returns to the level observed below the overlap region. In Figure 8d, we notice that the velocity near the channel floor is high due to the continuity equation, which dictates that a smaller flow cross-sectional area results in a higher velocity. However, the velocity decreases significantly as we move upward when the main screen and sub-screen overlap. This decreased velocity continues as we move further upward. Thus, we note that Figure 8a-d provide insights into the potential stress variations that various components of the WTP may experience in the vicinity of WSM. The approximate speed of the debris is estimated by the average velocity decrease, as shown in Figure 9. For a constant inlet velocity of 0.2 m/s, the outlet velocity is reduced by 0.60% and 0.71% in the cases where the sub-screen is fully and partially lowered, respectively.