Mathematical models of sediment transport usually assume the sediment particles as passive tracer and neglect the feedback effect of sediment resuspension on near-wall momentum transport. In the present research we attempt to quantify the above mentioned effect with the aim of gaining better description of sediment-turbulence interaction. We carry out Large Eddy Simulations (LES) of noncohesive sediment transport in open channel flow at Re= 600. The simulations are based on the singlephase approach in which the sediment phase is treated using an advection-diffusion transport equation for the sediment concentration. The flow over the sediment bed obeys the incompressible 3D Navier- Stokes equations under the Boussinesq approximation for buoyancy effects. Two-way coupling model is employed where the effect of suspended sediments on flow field is considered as density variation in gravity term of Navier-Stokes equation. Analysis of simulation results is carried out based on time-averaged profile of streamwise velocity and concentration field for both one-way and two-way coupling models. In presence of high suspended sediments in water column, the averaged concentration profiles reveal significant difference between one-way and two-way coupling approach due to buoyancy effects. It is remarkable that feedback effects are negligible in case of large grain size when the reference concentration is small at the wall and deposition flux is large. The time-averaged streamwise velocity profile shows that stratification effects reduce the von-karman constant which is in agreement with previous studies. The visualization of instantaneous low-speed streaks is also confirmed the stratification effects on the near wall region.

Large Eddy Simulation of suspended sediment transport

DALLALI, MARYAM;ARMENIO, VINCENZO
2014

Abstract

Mathematical models of sediment transport usually assume the sediment particles as passive tracer and neglect the feedback effect of sediment resuspension on near-wall momentum transport. In the present research we attempt to quantify the above mentioned effect with the aim of gaining better description of sediment-turbulence interaction. We carry out Large Eddy Simulations (LES) of noncohesive sediment transport in open channel flow at Re= 600. The simulations are based on the singlephase approach in which the sediment phase is treated using an advection-diffusion transport equation for the sediment concentration. The flow over the sediment bed obeys the incompressible 3D Navier- Stokes equations under the Boussinesq approximation for buoyancy effects. Two-way coupling model is employed where the effect of suspended sediments on flow field is considered as density variation in gravity term of Navier-Stokes equation. Analysis of simulation results is carried out based on time-averaged profile of streamwise velocity and concentration field for both one-way and two-way coupling models. In presence of high suspended sediments in water column, the averaged concentration profiles reveal significant difference between one-way and two-way coupling approach due to buoyancy effects. It is remarkable that feedback effects are negligible in case of large grain size when the reference concentration is small at the wall and deposition flux is large. The time-averaged streamwise velocity profile shows that stratification effects reduce the von-karman constant which is in agreement with previous studies. The visualization of instantaneous low-speed streaks is also confirmed the stratification effects on the near wall region.
978-1-138-02674-2
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11368/2831519
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