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The “Coanda effect” is named after Henri-Marie Coanda, a Romanian scientist, who first identified the effect in 1910, and involves the tendency of fluids to follow a surface.
The basic principle of the Coanda effect screen operation is shown on the figure below. The screen is installed on the downstream face of an overflow weir. Flow passes over the crest of the weir, across a solid acceleration plate, and then across the screen panel, which is constructed of wedge-wire with the wires oriented horizontally, perpendicular to the flow across the screen. As the flow passes over this surface, the shearing action of the bars combined with the Coanda effect, separates the flow. Clean water passes down through the screen, while the water containing fish, sediment and debris passes over the screen to rejoin the water course below the weir. According to the manufacturer, the screen is self-cleaning, it can operate without any external intervention to remove debris from the screen, and has a desilting function and excludes most of the particles whose diameter is above half of the aperture size of the screen.
The main drawback of this type of intake is the head loss due to the layout. Full height screens are 1.2 m high and 0.7 m high screens are also available.
Schematic of Coanda effect screen (© Dulas Ltd) |
