Local erosion and mound formation induced by turbulent slurry wall jets in crossflow

Abstract

This paper presents the results of experimental investigation on the local erosion and mound formation induced by slurry turbulent circular wall jets in crossflow and with the presence of a secondary current. The trajectory of the slurry jets with different intensities on the bed formation was measured with an accurate laser scanner with a resolution of ±1 mm. Other data such as scour, and mound areas and volumes were measured to study the effects of sediment concentration and jet’s intensity on deformation of erodible bed at the vicinity and downstream of the crossflow. Experimental results indicated that the mass flux of sediment in slurry wall jets increased the width and spreading rate of sediment mound while increasing the intensity of the jet reduced the mound width and stretched it along the flow direction. The correlation between non-dimensional geometry parameters with the jet’s Reynolds number indicated a distinct behavior on the development and direction of mounds with a threshold Reynolds number of approximately 36,000. For turbulent slurry wall jets with Reynolds number smaller than the threshold value, most of the sediments settled at the vicinity of the nozzle and reduced the scour depth while for stronger jets, sediment dunes were formed in the curved region of the flume and scour depth was almost the same as the scour depth formed by the corresponding clear water turbulent wall jets. A linear correlation was found between the peak scour depth and jet’s Reynolds number, while peak scour depth, area, and volume decreased with increasing the initial sand concentration of slurry jets. Empirical formulas were proposed for prediction of bed deformation and jet’s trajectory, the accuracies of the proposed models were evaluated using statistical analysis, and the performance of the proposed models were compared with the existing models from the literature.