Segregation of Particles in Multi Size and Density Beds by Circular Wall Jets

Abstract

AbstractLocal scour formation over uniform beds and downstream of a circular wall jet has been studied in the past. From the engineering point of view, the location of the maximum scour depth and its magnitude are important for proper erosion prevention plan and riverbed restoration. Many empirical equations have been proposed to correlate the hydrodynamic variables of wall jets with scour characteristics. The present study provides the results of a series of laboratory experiments on scour development induced by a three-dimensional confined circular wall jet on multi-size and density beds. A nozzle with a diameter of do = 0.0127 m was used to generate wall jets with different flow rates ranging between Q = 22.2 and 32.1 L/min and different tailwater levels yt = 0.1016 and 0.1524 m were tested. The maximum scour depth, width, and length were measured in steady-state flow condition and similar tests were conducted with uniform sand beds for comparison. The selected mixed bed in this study represents a specific mine ore in the Northern Ontario, Canada. The results are useful for understanding scour formation in such mixed beds and identifying material segregation in preliminary mining operations using a clean energy technology. Two-sequence scour depths were formed in the mixed bed and it was found that the maximum scour depth occurred in the first sequence. The maximum scour depth, width, and length were found to be a function of the densimetric Froude number. It was found that the jet tends to group each material inside the scour hole and the area of the armor layer was 43.5% of the total eroded area. The armor area formed by the Lead and Magnetite particles and such area increased with decreasing tailwater level by approximately 6%. Whereas the sand area did not change significantly with tailwater depth variations.