[harsha28]

Hello,

My name is Harsha and I am currently working on simulating flow through a channel for a graduate project. I have been having some issues with the simulation. Below is the a walk-through as to what it is that I am doing and what the problems are.

1. I am trying to simulate the flow through a channel. It flows into a moving bed. Attached is an image of the figure. (Channel.JPG).

2. My current mesh is of the size 9e-005 with 22035 nodes and 19108 elements. I do know the mesh size is still large, but I reduced them to decrease the simulation time. (Mesh.JPG)

3. Since air comes into play as soon as the liquid comes out of the cylindrical channel, I have modeled this as a Multiphase flow with liquid and air.

4. Now, I am doing a pressure based steady simulation ( I have tried both steady and transient). I use Implicit VOF with the default Volume Fraction cutoff (1e-06). I have not considered the surface tension.

5. The two phases present are liquid (Density = 1250 kg/m3 and viscosity = 1000 kg/m-s) and air (Density = 0.01 kg/m3 and viscosity = 0.01 kg/m-s)

6. The inlets, moving wall and outlet boundary conditions are specified. The others are walls and symmetry. (BC1.JPG and BC2.JPG). I also set the respective volume fractions and inlet velocities.

5. After I initialize the solution from inlet, I run the simulation. The convergence criteria is 0.001 for all of them. Now, here is something that I do not understand. With transient, I have played around with different values of Max number of iterations, time steps and time step size and the solution does not seem to converge most of the times. When it converges in some time steps, it does not stop and goes ahead to complete the maximum number of iterations. What does this mean?. Shouldn't the computation stop once it reaches convergence?

And with steady, the solution does not seem to converge at all. Someone please get back to me about this. This would be great help.

Please let me know if more details are needed. I am using a coupled scheme with green- gauss node based gradient, PRESTO! pressure, QUICK momentum and Modified HRIC Volume Fraction. Not only does the nature of the flow make any sense there is also a small gap between the moving substrate (bottom) and the flow channel that I cant seem to eliminate (Flow.JPG).

[rupak504]

Using VOf without considering "Surface tension" has got no meaning.