# CFD of Multiphase Model

1. Jan 10, 2012

### vaibhavkhare

I am using VOF model for simulating..but within 1 or 2 time step courant number reach its limit and iteration stops..i reduced the time step size from 1 to 0.05 but there is no result of it..and i have to simulate it for around 1hour..
how can it be possible to increase courant number..or what is its concept..

2. Jan 11, 2012

### the.drizzle

You'll need to provide much more information than that in order for anyone to be able to help you, I'm afraid. What software package are you using? Can you provide some details about the mesh / BC's? After you one hour of simulation (which, I would add, isn't much time at all in terms of CFD simulations) what is your Courant number doing?

Recall that the Courant number is defined as

$C_0=\frac{\delta t \left|U\right|}{\delta x}$

and what you need to do is keep the maximum Courant number below unity for each time step for every cell in your mesh.

3. Jan 12, 2012

### vaibhavkhare

ohkk..i am using FLUENT 6.3 for simulation and GAMBIT 2.4 for meshing and drawing.
i am working on a close box which is 40% filled with water and heated from bottom.. There is 1 pressure outlet on the upper side of box and no flowing situation of air or water. By using VOF multiphase model i want to do simulation on it.
The meshing type of model is HEX.
i am using turbulence model also for simulating the flow of mixture.
The simulation is not working for 1 hour..it ends only after 2-3 sec with a error that the courant number in excceded its maximum limit.. I reduced the time step size but there is no effect on that.

4. Jan 12, 2012

### bigfooted

I would start with a vof tutorial case and then modify it in steps until it matches your problem. You will then have a working problem as a starting case.

Note that some vof problems require very small time steps. in one of the fluent tutorials I have checked, the time step was 1e-8.

5. Jan 16, 2012

### polka129

hello ...i am trying to perform CFD analysis of a simple savonius wind turbine .made a CAd model in solid edge.have made the mesh in gambit and imported it to FLUENT for analysis..there is a problem.fluent is NOT analysing the blades.it is skipping it.

solution?