# Hydraulic Analysis of a Passive Wedge Wire Water Intake Screen for Ichthyofauna Protection
## 4 Discussion  
Although some areas are experiencing a decline in water demand, the total amount of water captured for municipal as well as industrial purposes worldwide continues to increase. High inlet velocities to surface water intake with high capacities, especially those for cooling purposes, pose a very high threat to ichthyofauna. Migrating fish of small size or juveniles with poor swimming skills are dragged in, maimed, and killed. Similar risks are posed by turbines in hydroelectric power plants. The studies conducted on a cylindrical wedge wire water intake model showed a significant reduction in maximum inlet and approach velocities around the screen surface at similar intake capacities. In order to reduce the non-uniformity of the inflow velocity distribution around the screen surface, it was proposed to install first a deflector with uniform openings and then with non-uniform ones. The smaller openings were located on the suction side of the pump. Both proposed deflector designs significantly bridged the inequalities between water inflow velocities to the screen surface. As expected, the proposed uneven distribution of perforations in one of the deflectors allowed for a more even distribution of inlet and approach velocities to the screen surface. However, from a practical point of view, the differences between the two proposed deflectors were small. The differences between the maximum inlet velocities (Vmax) as well as between the quotients Vmax/Vmin of the inlet velocities for deflectors with equal and unequal hole sizes did not exceed 25%, and between the quotients Vmax/Vav of the inlet velocities for both types of deflectors did not even exceed 4%. As one moved away from the inlet surface into the cylinder, the differences between both types of deflectors decreased and, at a distance of 5 cm from the surface, the maximum velocities were identical for deflectors with equal as well as unequal hole sizes. The results of the experimental and numerical studies of the developed water intake model designs allowed a detailed analysis of the inlet and approach velocity distributions around the cylindrical wedge wire inlet screen, as well as a detailed visualization of the current lines around the analyzed screen and information on velocity vectors. The developed intake model allows safe intake velocities for ichthyofauna while maintaining sufficiently high yields. The models developed had relatively low pressure losses, both in the absence of and with deflectors. The experimental and numerical studies carried out showed the smallest approach velocities at the top and the highest at the axillary level. Information on the distribution of approach velocities to the cylinder screen in the vertical cross-section makes it possible to identify areas more or less at risk of attracting juvenile fish or floating elements. Studies show that the greatest such risks will occur at the axillary level of the cylinder screen. In contrast, it will be the smallest in the area above the cylinder, especially when a deflector with equal openings is installed inside. This also means that there is less of a risk of dragging in, not only fish but also ice and snow that may be present above the screen in the winter period. The results obtained from numerical calculations and experimental tests had high agreement. This demonstrates the correctness of the methodology adopted during the experimental studies as the correctness of the mathematical model adopted in the numerical calculations of the RNG k-cross significantly lower (renormalization group applied to Navier Stokes equations). This model is suitable when different types of flows occur in different areas of analysis. For the analyzed water intake inlet pipe capacity without the screen, the inlet velocities far exceeded acceptable standards. Installation of the cylindrical screen increased the area of the intake and significantly reduced inlet and approach velocities, but they were still too high in some areas of the screen.