Numerical Study on the Effect of Sediment Concentration on Jump Characteristics in Trapezoidal Channels

Abstract

Hydraulic jump is a phenomenon observed in open channel flow, and studying it has been a challenge for scientific communities. Most of the previous studies on this topic have been devoted to the cases of clear water in rectangular geometry. However, in nature river flows carry sediment loads; meanwhile, trapezoidal stilling basins are proved to be more economical as well. In this paper, the RNG turbulence model has been used to simulate jump characteristics in a symmetrical trapezoidal channel of 45° side slope for clear water flow and three different sediment concentrations of 4%, 8% and 12% and a range of initial Froude number between 1.5 and 12. The results indicate that by increasing the sediment concentration the bed shear stress amounts and energy loss ratio increase while the length of jump ratio decreases. In comparison with the clear water flow, for the case of Fr₁ = 7 and sediment concentration of 12%, the length of jump ratio decreases by 18.1%, the sequent depth ratio increases by 17.2% and the energy loss ratio increases by 3.2%. Furthermore, the bed shear stress at the beginning and at the end of the jump is innovatively investigated. The results show that the shear stress at the initial depth section is not dependent on the sediment content, but at the secondary depth of flow, it is highly dependent on the suspended sediment loads content.