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Victor November 7, 2002 07:28

Massconvergence VOF
Hello! Im working on a project that concerns two-phase flow of air and water in a pipe. Im using the VOF-model in Fluent 6 and I have encountered a few problems. This is the first: When I, after convergence of the simulation, go to check the fluxes I find that the massflow out of the pipe differs alot from the massflow at the inlet! I then run a new simulation and use a monitor at the outflow surface to monitor and plot the massflow. This showed that the massflow out of pipe varied between 1/10 to 5 times the massflow at the inlet!

Does anybody know why this is happening?

Thank you! /Victor

david November 9, 2002 22:55

Re: Massconvergence VOF
Your problem is still unsteady (if converges properly)


Victor November 10, 2002 06:58

Re: Massconvergence VOF
Ok, but how about the law of massconservation? November 11, 2002 14:32

Re: Massconvergence VOF
Hi, If you do 5 sec unsteady simulations, you should check:

[Total mass in-total mass out= total accummulation] in this 5 secs Are you checking mass flux at certain time?


Victor November 12, 2002 03:56

Re: Massconvergence VOF
Hello David!

First of all I would like to thank you for your answers.

The answer to your question is that I check the mass flux at every time step. To me it looks like the massflow in average over a number timesteps is somewhat equal to the constant inflow. So maybe if I collect the values of the outflow and calculate an average, I could get some proper results? But this will still not cut it for me because in my problem I have two outflows and I`m interested in how much of the incoming water that goes out of the outflows respectively. The only way I know to do this is to check Report/Fluxes/Massflux, choose water and then pick the inlet and the two outlets. But this will only give the result at the last timestep simulated and not some average for the whole simulation. So Im still a bit confused...

Another thing... What do you mean by total accummulation? and how do I check it?


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