Study On Hydrodynamic Characteristics And Discharge Capacities Of Airfoil-Shaped Gutter Grates

To improve the discharge capacities of gullies, lattice bars with rectangular cross section of standard gutter grates widely used in engineering were designed as airfoil-shaped gutter grates with a streamlined structure cross section. Based on physical model test, we chose Froude number as similar criterion. And ratio of geometric scale between test grates and engineering prototype grates was 1:1. In the experiment, the hydrodynamic conditions of flow running into gully were changed by setting longitudinal slop of the channel and angle of deflector, airfoil-shaped grates tested were classified as 4 categories, with incling angles of lattice bars meeting inlet water were 30°,45°,60° and 75° respectively. Besides, both the standard grate and the grates with column lattice bars were compared to test. too. The hydrodynamic characteristics and discharging capacities of grates tested were researched.1) There was no significant difference between airfoil-shaped grates and two kinds of grates compared, with grates discharging flow along the longitude slope. The structure of flow discharging on the surface of airfoil-shaped grates was similar to the others, which were composed of three parts, mainly including continuous flow area, discharging boundary layer and broken flow area. Airfoil-shaped grates had larger discharge flow capacities of keeping continuous nappe discharging on their surface than the others. Among those,30° and 45° airfoil-shaped grates preserved the maximum flow with continuous nappe discharging.2) The hydrodynamic conditions of the water running into gully had great influence on the maximum discharge capacities of grates, the discharge capacities can get larger, with larger inflow depth and smaller Froude number. The discharge coefficient of grates when lattice bars discharge flow can be calculated by orifice flow approximately. Moreover, among all grates tested 30° and 45° airfoil-shaped grates had the maximum average discharge coefficients, accordingly both capacities were the largest. And discharge coefficient of the standard grates was the minimum.3) The ways calculating the length of nappe discharging on the grates were discussed. The functions among nappe length L, hydrodynamic conditions of water flowing into gully, including flow rate Q and Froude number Fr, and discharge coefficient of grates μ were builded. With analyzing factors influencing water nappe length, results showed that flow rate Q and Froude number Fr played greater roles, and discharge coefficient of grates μ had the least influence.