In this paper results obtained from laboratory studies of scouring in sediment bed with non-cohesive materials in the downstream of an apron due to a submerged horizontal jet are reported. Results showed that under different experimental conditions, there was good agreement among curve of dimensionless scouring profiles. Also, it was found that the dimensionless scouring profile is independent of changes in all parameters effective on scouring mechanism such as; discharge, jet velocity, thickness of jet, time, tailwater depth and diameter of sediment particles. Equation of dimensionless curve unit scouring holes profile has been obtained as a sine and cosine combined relation. Time changes of scouring holes depth has been fitted with a logarithmic relation. As another result, for a fixed thickness of jet and with a fixed tailwater depth, by increase in densmetric Froude number (Frd), dimensions of scouring profile will increase. Test time didn't have any effect on trend of scouring profile dimensions change pro rate of Frd. In deep submerged jet, trend of scouring development was natural and with passing of time scouring becomes balanced, but in shallow submersed state, the jet flow was found unstable. This was accompanied by bed erosion, transportation materials and filling some part of scouring hole consecutively. Similar tests to what mentioned above, were performed on the bed which was protected with rip-rap (bed beaching). The most recent test results showed considerable decrease in dimensions of scouring profile, so that the average decrease by rip-rap in scouring holes balanced depth was equal to 38%, having a maximum of 65% and a minimum 13%. With use of dimensional analysis and theory of Buckingham, general relations for values of scouring profile dimensions as a function of dimensionless and effective variables, jet velocity, thickness of jet, tailwater depth, time, and densimetric Froude number, were experimentally obtained.
展开▼
