Scour Reduction by Air Injection Downstream of Stilling Basins: Optimal Configuration Determination by Experimentation

摘要

Hydraulic structure undermining attributable to scour can cause structural damage or collapse. Experiments were performed in a laboratory channel on scour downstream of a stilling basin of a low-head spillway to ascertain the feasibility of air injection for scour reduction, an idea that has not been previously attempted. Various hydraulic flow conditions without air injection indicate that the condition of stilling basin water elevation lower than the spillway crest, under high headwater-to-tailwater depth ratio, results in the deepest scour. Over 120 experiments were performed to determine the optimal parameters for scour reduction by air injection. It was found that optimal scour-reducing conditions consist of (1) air injection at an air-to-water velocity ratio of 251, (2) vertical air injection at the same elevation as the stilling basin exit point, (3) using diffuser hole diameters corresponding to a ratio of air-to-water velocity equal to 251 spanning the entire width of the stilling basin, and (4) a diffuser hole spacing 0.04 times the diffuser width. Scour can thus be reduced by approximately 59% near the structure. Air compressors and diffuser pipe diameter and hole sizes corresponding to these conditions would be required in prototype installations.