## 4 Results and Discussion
### Effect of the WSM on the Flow Distribution
#### 4.1.2 Flow Distribution When the Rake Is Operational  
Figure 10a and b show the normalized velocity magnitude contours on the longitudinal vertical plane \(y=0.1\) m for the posterior and the vertical positions of the rake, respectively. These positions of the rake were chosen to represent the flow disturbance for the entire path of the rake because they create the most disturbance, that is, disruption is created as the rake enters the flow from behind. The vertical position was chosen because the rake front  
is highly exposed in this position. The arrows in Figure 10a,b represent the velocity field. The length of these arrows is proportional to the velocity magnitude--the shorter arrows indicate slower flow, and the longer arrows indicate faster flow. Fluid enters the channel in the positive x-direction at 0.2 m/s and passes through the screening mechanism. In either case, severe flow separation is observed in the vicinity of the rake during its operation time. However, any separation created by the rake is dampened by the time the fluid reaches the outlet. Therefore, the rake does not create a substantial non-uniformity over the cross-section of the channel at the outlet. Figure 8: Effects of different inlet velocities and sub-screen positions: upstream velocity (at location C) when the sub-screen is (**a**) fully lowered and (**b**) partially lowered; downstream velocity (at location D) when the sub-screen is (**c**) fully lowered and (**d**) partially lowered. Figure 9: Variation in flow average cross-sectional velocity along the flow direction at 0.2 m/s. The effect of the rake operation on the components at the inlet of the WTP is further investigated in Figure 10(a),b, which depict the magnitude of the x-component of the velocity over the \(y=0.1\) m plane for the posterior and the vertical positions of the rake, respectively. The shorter arrows indicate a slower flow, and the longer arrows indicate a faster flow. The velocity abruptly changes value at the outlet whilst the rake is operational, thereby suggesting an unsteady stress application on the components at the inlet of the WTP. Therefore, the design of the components at the inlet of the WTP should account for rapid velocity fluctuations throughout the rake operation. The flow profile in the immediate vicinity of the rake is highlighted in Figure 10(a) and b for the posterior (\(\varphi_{\text{r}}=-75^{\circ}\)) and the vertical (\(\varphi_{\text{r}}=0^{\circ}\)) positions of the rake, respectively. Specifically, in Figure 10(a), a wake region is developed near the posterior edge of the rake head whilst the rake is in the posterior position. No wake region is developed near the frontal edge of the rake head, thereby resulting in higher stresses in this region whilst the rake is in the posterior position. This trend is reversed when the rake is in the vertical position, as highlighted in Figure 10(b). In this figure, a wake region is developed near the frontal edge of the rake head whilst the rake is in the vertical position, whereas no wake region is developed near the posterior edge of the rake head. This condition results in higher stresses on the posterior end of the rake head whilst the rake is in the vertical position. Figure 10: Normalized velocity contour plots at \(y=0.1\) m for an inlet velocity of \(0.2\) m/s when the rake is operational and (**a**) \(\varphi_{\text{r}}=-75^{\circ}\); (**b**) \(\varphi_{\text{r}}=0^{\circ}\); the view of the rake has been magnified, and the arrows represent the velocity magnitude at the trailing points. The portions of the channel before and after the WSM are called the upstream and downstream regions. The velocity is plotted at a distance of (X-axis) 0.5 m away from the WSM in the upstream region (location C) in Figure 12a for the posterior and vertical positions of the rake. Similarly, velocity is plotted at a distance of (X-axis) 0.5 m away in the downstream channel of the WSM (location D) in Figure 12b for the posterior and vertical positions of the rake.