Reclamation Information Sharing Environment (RISE)

Coanda-effect screens exclude coarse and fine debris from a variety of water intakes, including small hydropower installations, irrigation diversions, and stormwater runoff facilities. High velocity supercritical flow passes over an inclined wedge-wire screen panel with specially tilted wires that shear thin layers of water from the bottom of the water column and through the screen. The screens have high capacity and are hydraulically self-cleaning, making them well suited to remote sites without electrical power. The flow conditions vary significantly over a typical screen. Previous testing has indicated that screen capacities are affected by gravitational, surface tension, and viscous forces, but the range of tested flow conditions has been limited compared to the potential applications. In this study, small sections of prototype screen materials were tested in a variable-slope flume. Screen discharge coefficients were calculated from the test data and related to the Froude and Weber numbers of the flow. Tests conducted over a range of water temperatures showed that screen performance is independent of fluid viscosity but depends strongly on surface tension. Several screen materials were tested, and the performance of all screens could be modeled with relations having a common functional form. Individual screens exhibited unique performance characteristics, but nine of the thirteen tested screens performed similarly, and their performance was effectively modeled as a group.