AN EXPERIMENTAL STUDY OF FACTORS INFLUENCING THE SCOUR DEPTH RESULTING FROM THE COLLISION OF WATER JET IN STILLING BASIN FLOOR

When excess water is discharge from a reservoir into the downstream water body, it sometimes flows in the form of a jet. This jet will have a high kinetic energy making it able to transport the sediment particles downstream of the impinging area, thereby forming a scour hole. The purpose of conducting this study was to evaluate the depth of the local scour result by free water jet based on the laboratory experiments and numerical analysis FLOW3D. One hundred and thirty-eight runs were carried out to investigate the local scour downstream the hydraulic structure under clear-water conditions with different discharges, tail water depths, and jet angles. Two types of jets were used, normal jet and dispersion jet. Results indicated that maximum scour depth increase with increasing densimetric Froude number and jet velocity. The increase in tail-water depth increases the scour depth until access to a critical depth at which the maximum depth is occurring after that the scour starts downward when the depth is overstepping the critical value. The optimum jet angle depends on the jet discharge, with a value of 20° for jet discharges 60-80 L/min, and 40° for Jet discharges 100 and120 L/min, which cause minimal depth of scour. The scour depth values under dispersion jet are smaller than those under normal jet. Generally, the reduction percentage increases with the increase of jet discharge, as it 30.7% and 78.7% for discharge 80 and 120L/min respectively. The numerical simulation was used by (FLOW3D) software program to investigate from the result of the experimental work, the results showed that there was a very good agreement with the experimental work with average 95.25%.