Gravel bedform simulation by Ansys Fluent
 

Aim of Simulation
 

It depends on the objective of the simulation. If you wish to study flow of water over as well as through the gravel bed, then it has to be treated like a porous zone. If the objective is only to study the flow of water over a gravel bed but affected by the gravel's presence, then you can model it as a rough wall. If you want to study erosion/accretion/movement of gravel, then you have to use multiphase simulation.

Thank you mr.vinerm

I want to study flow over gravel bed and show how the velocity profile change with depth and also study energy dissipation over this bed.
can you help me about this questions,please
how can insert or represent the roughness of open channel in fluent? if you can guide me by vedio on youtube or a pdf about this subject I will be very grateful to you .
which model more proper to used in this study (k-epsilon,k-omega or other model)
how can I insert discharge of flow as an initial condition?

Flow over rough surface
 

To model flow over a rough surface, you have to use model with Standard Wall Function. Only SWF provides option to include wall roughness. This option will be available under Boundary Conditions > Walls.

I could not understand what you mean by initialization of discharge of flow.

thank you very much for your response , i work on experimental discharge equal 15 L/sec, i want to know how can simulated that ?

Discharge
 

That's just a boundary condition. Since the flow is incompressible, you can either use constant velocity or constant mass flow rate at the inlet. During initialization, you can specify if you want full domain to be filled with water or up to a certain height. If you run a steady-state simulation, then it won't matter even if you start with full channel filled with water.