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-   -   Problem with 2d VOF Simulation (http://www.cfd-online.com/Forums/fluent/40332-problem-2d-vof-simulation.html)

 David March 27, 2006 18:42

Problem with 2d VOF Simulation

Hi I am a undergraduate student doing my honours project on fluent.

I am looking at the effects of the collapse of a wave on a beach and effects on the beach as this wave flows rushes up and down the beach.

I am using the 2d Volume of Fluid simulation in fluent 6 and I have adapted a region in my mesh and patched it with water to represent the wave collapsing onto the beach, however when I run the simulation I have to use a very small time step inorder for results to converge.

At present my time step is 5e-08 and after 7860 iteration the flow time is only 0.001366s seconds and it seems like it is taking an eternity to run and due to a lack of licences this is a major problem.

I was wondering if i have maybe made a mistake in setting up my simulation and i would be very grateful for any help given.

My mesh is a simple rectanglur channel 0.55 meters by 6 meters. The mesh spacing is 0.005.

My solver settings are: 2d, segregrated, implicit, time - unsteady, velocity - absolute, 1st order, cell based, superficial.

Multiphase - Volume of fluid. 2 phases; air and water, water patch into region.

K-epsilion viscous model used. Momentum and Energy models not changed.

Operating conditions - Pressure located at top of mesh. Gravity is on on with X=0 m/s-2 and Y = -9.81 m/s-, specific gravity = 1.225.

Boundary conditions - all verticies are walls.

The turbulent velocity is 0 and in the solution control- Pressure discretization is standard and PISO is the Pressure-Velocity Coupling method.

Please reply to this post if you can help or email me at u11djs2@abdn.ac.uk to get in touch.

Yours sincerely David

 Kharicha March 28, 2006 03:04

Re: Problem with 2d VOF Simulation

To make easier your calculations:

use slip condition at the wall. For the begining set the surface tension to zero.

perform a calculation without VOF, to make the flow and the turbulence quantities converged. For that you can use a relatively high time step, and one iteration per time step. If this is not ok, you might have a problem with the turbulence calculations. So check that.

Once this is converged, switch VOF on, start your calculation (with surface tension). With small time step 10-4, and 10-20 iterations per time step.

Keep in touch.

 Frederik March 28, 2006 04:12

To Kharicha:VOF 2phases+heat source..pls help!

I'm runing 2 phases VOf model with deformation of the free surface, I need to define a heat source only on the primary phase material, the heat source decreases lineary from the interface with respect to the vertical distance(y axis)...please can you give me some suggess or advices to doing this, thanks in advance, Frederik.

 Kharicha March 28, 2006 05:27

Re: To Kharicha:VOF 2phases+heat source..pls help!

This is a little hard... don't you have an equation which can describe the magnitude of your source?

 Frederik March 28, 2006 06:06

Re: To Kharicha:VOF 2phases+heat source..pls help!

Dear Kharicha, The heat source decreasing exponentialy ..as Q*exp(-a*y), where "a", (a >0) is constant..but I can as first approximation use a constant heat source Q, but I need to define it just on the primary phase (also in this model the free interface is deforming, its geometry changes)... How can I do it? ..help please..!

 اhosna rezaveisi April 12, 2006 08:24

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