### Session S20 - Applied Math and Computational Methods and Analysis across the Americas

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## The evaluation of two-fluid model for suspended sediment transport using Direct Numerical Simulation

### Hyun Ho Shin

#### Universidad Nacional de Asunción, Paraguay - This email address is being protected from spambots. You need JavaScript enabled to view it.

The sediment transport in a horizontal open channel flow can be represented as two-phase flow, where the water flow is considered as a continuous (liquid) phase, and the sediment particles as a dispersed (solid) phase. Among the two-phase flow modeling, two approaches can be considered: (i) point-particle Direct Numerical Simulation (DNS), and (ii) two-fluid models. In the point-particle DNS, the continuous-phase is modeled by incompressible Navier-Stokes equations where all the turbulence length and time-scales are solved detailly, and each particle considered as a point-source is tracked individually. On the other hand, in two-fluid models, both phases are considered as the interpenetrable fluids represented by two sets of averaged equations for mass and momentum. As the particle concentration of the suspended sediment is very dilute, it is commonly accepted that the one-way coupling situation is a good approximation, i.e., the fluid-particle interactions influence only on the dispersed-phase, and the continuous-phase is not affected by the presence of the particles.

Although, the two-fluid models are more adequate for the engineering applications, the point-particle DNS is used for the fundamental investigation to study the dynamics of the phenomena. In this context, the point-particle DNS can be useful in the subside for the development of two-fluid models for the engineering flows in sediment transport. In this work, the point-particle DNS is used for the evaluations of two-fluid models. The averaged equation for the particle momentum is developed in the context of point-particle one-way coupling, and then, the balances of different fluid-particle interactions are evaluated. We show that in the absence of gravity, the interplay between the stress-gradient force and the turbophoretic effects is dominant. On the other hand, when gravity force acts in the wall-normal direction, the dominant forces are gravity and drag. In two-fluid models, both stress-gradient and turbophoresis can be modelled in terms of fluid Reynolds stresses, and for the drag force, it has to be included a model for the drift velocity.

Joint work with Luis M., Portela (Delft University of Technology, The Netherlands), Christian E., Schaerer (Universidad Nacional de Asunción, Paraguay) and Norberto, Mangiavacchi (Universidade do Estado do Rio de Janeiro, Brasil).