Free Surface Flow with Sediment Transport
 

Hello CFX Folks,

I am trying to simulate flow over an embankment weir (small trapezoidal dam) where as the bed is mobile. I was successful in simulating the hydrodynamic part, but now I would like to include the effects of the mobile bed. So I believe it is possible to simulate the transport of sediment in three ways:

1- Eulerian-Eulerin Multiphase 2- Lagrangian Particle Transport (although CFX won't let me include two Eulerian-Eulerian models or two continuos phases like air and water with a dispersed phase like solid particles using the Lagrangian model) 3- Create a new material (water and sediment) and an additional variable such as concentration and solve a transport equation (e.g. Poisson or diffusive transport)

I would like some advice on how to define each phase in each of the cases above (if possible. I have a feeling the Lagrangian Particle Transport will not work because the air and water phase cannot both be continuous wtih a dispersed solid phase. I know this has been done before, and I'm sure there is a way around it).

Your help is very much appreciated. Thanks!

Regards, M. Riffai

Re: Free Surface Flow with Sediment Transport
 

Hi,

This sounds like it would be best done as a discrete element model. These type of models can account for particle size and packing, settling and motion. At the moment you need to couple to a package like EDEM to do this, but I hear that CFX V12 has some capability in this area. Not sure if it will do what you are looking for.

Regards, Glenn

Hello M. Riffa,

Finally, how did you define this model?
Option 1, 2 or 3? I'm really interested in this system.

I had several problems with option 2 as well, but I think it's the best approach. I wouldn't define solid particles as a "solid dispersed". On the other hand, air and water continuous phases are necesary.

Thanks a lot

HI
I wanna model the pickup rate as expression mentioned by van.Rijn as follow:
P=0.00033(tet-tet_cr/tet_cr)^1.5 * (s-1)^0.6 *g^0.6 *d^0.8/nu^0.2

which ni is diffusivity and s is ratio of densities and d is particle diameter.
How could I nondimensional this expression and relate it to froud-Numbewr and Reynold?

Thanks