## Fluids

#### How to model a free surface with VOF for CFD and CHT?

• Marie1234
Subscriber

Hello,

I'm doing a steady state 3D CFD-simulation in FLUENT with CHT and for modelling the free surface of my tank ( 70mm x 150mm x 100mm) I use VOF.

In my tank i have 9 cylinder of aluminium with a heater inside with "Energy Source".

I have an inlet and outlet with e little pipe (diameter 6,5 mm x 40mm).

The materials are air (phase 1, density: incompressible ideal gas) and oil (phase 2) and the filling level is 85mm (of 100mm).

viscous model : laminar

My Operating Conditions are: pressure=101325 Pa, density = 1.225 kg/m^3

BC : velocity inlet: v = 0.703 m/s, T = 296.95 K

pressure outlet : 1) outlet: pressure = 0 Pa

2) atmosphere (opening of the tank) : pressure = 0 Pa

Solution Methods: presure-velocity coupling : Scheme Coupled (Coupled with Volume Fraction in also enabled.)

Diskretisation : default

Solution Controls: default (but Momentum = 0.4)

The problems:

• In the beginning, the conti-equation isn't satisfied, so i have more oil coming in than going out, so my filling level increases. But I want a constant volume of oil in the tank. I cannot enable Coupled Level-Set + VOF because I get this Warning : "Level set model is not supported for mesh containing polyhedral cells".
• I do a pseudo transient simulation with the defaults. After 200 - 300 iterations, the temperatures go crazy ( 1500 °C or -200 °C) --> "Floaing point exception". Should I change the Time scale Factor for a better convergence?

This is how i initialized the model:

• DrAmine
Ansys Employee
Use unsteady solver if you want to get reasonable results. Do not use Level Set only because you have heard that it might be better: that is not always true. And yeah with polys it is not available. n
• Rob
Ansys Employee
If you want a constant height of liquid you want to check the outlet condition: what's holding the liquid level up? n