Comparison of the CFD softwares: Jadim and Fluent with experiments

We will compare the simulations with Fluent and Jadim with the experiments, which are movies of oil and water flow in a certain geometry with and without connectivity.

The valves can not be completely opened in the experiments, therefore we will see if respecting the ratio between the hole area and the total area of the valve will have an impact on the simulations.

$$\rho_{water} /\rho_{oil}$$ (kg/m3) $$\nu_{water} /\nu_{oil}$$ (Pa.s) $$ \sigma_{oil/water} $$ (N/m)
1000; 800 0.001;0.01 0.025

  bottom valve closed bottom valve opened
equilibrium time (s) 36.7 19.3

The first simulation is made without ratio for the valves, here is a comparison between the VOF and level set method with the Jadim software.

$$\rho_{water} /\rho_{oil}$$ (kg/m3)
$$\nu_{water} /\nu_{oil}$$ (Pa.s)
$$ \sigma_{oil/water} $$ (N/m)
mesh size (cells)
mesh size (m)
1000; 800
0.1;1
0.025
70x88
0.35x0.44
VOF method on the left and Levelset method on the right.
 
 
VOF method with fluent (same parameters)
 

We have increase the viscosity 100 times to avoid numerical diffusion near the interface but the VOF method still present a lot of numerical diffusion and therefore does not show a equal equilibrium at the end: the iso-contour of oil volume fraction value of 0.5 is not at the same height at the end. The level set method does not show numerical diffusion and still has some problem on the wall, this problem comes from the code which is still developing currently at the IMFT and was firstly coded for bubbles.

Therefore we will continue the simulations with the level set method and try a geometry with ratio.

The results comparing fluent and jadim with the VOF method are the same on the flow versus time but fluent shows less numerical diffusion.

 

 

 

 

 

 

Bottom connected case

In this case, a simulation using level set method with a refine mesh with jadim is realized, for which the geometry is exactly the same with experiments,  the mesh is is refined, and the bottom of the equipment is connected.   

Mesh

$$\rho_{water} /\rho_{oil}$$ (kg/m3)
$$\nu_{water} /\nu_{oil}$$ (Pa.s)
$$ \sigma_{oil/water} $$ (N/m)
mesh size (cells)
mesh size (m)
1000; 800
0.02;0.2
0.025
280x352
0.35x0.44

 

Experiment                                                             Simulation with jadim-level set method

In the bottom open case, after the valve opens, the interface moves mainly  due to gravity as well as U tube effect, and finally reaches equilibrium, with the same flow pattern, oil on the top and water on the bottom.  It is observed that the equilibrium time to arrive the final steady state are similar with the experiment and  simulation, despite a difference in viscosity. Also, compared with the fluids movement during the experiment, in which the interfaces of water and oil rises or drops more steady.  With simulation with the method level set in jadim, more dispersed phase appears.

Bottom blocked case

 A simulation with a refine mesh to simulate the experiment bottom blocked case is also conducted.

$$\rho_{water} /\rho_{oil}$$ (kg/m3)
$$\nu_{water} /\nu_{oil}$$ (Pa.s)
$$ \sigma_{oil/water} $$ (N/m)
mesh size (cells)
mesh size (m)
1000; 800
0.02;0.2
0.025
280x352
0.35x0.44

Experiment

Simulation with jadim-level set

 

For the bottom close case, the movement is  mainly led by the density differences. The final flow patterns are the same for the simulation and experiment.  The equilibrium time to arrive the final state is  similar with experiment and simulation. The movement is similar, however, same with the bottom open case, more dispersed phase appears in the simulation.

Results analysis

In this chapter, different softwares and numerical methods, as well as the results,  to simulate the experiments are illustrated. In general, simulation with VOF and level set method both give a results where flow patten is similar with the experiments, although equilibrium times varies. 

With jadim, the VOF method shows serious problems of diffusion in the case viscosity setting is 100 times smaller than the original ones. The interface can not be clearly tracked. With level set, the interface can be tracked easily, despite lots of dispersed phase appeared. With fluent, the problem of diffusion is less severe. 

The level set method in jadim with blocks is settled  in the geometry,which is the case of the experiment, shows a closer results compared with the experiment when equilibrium time is concerned. The VOF method with fluent  using real parameters is considered a precise simulation, too. It is estimated if the geometry and the fluid parameters are set exactly the same with the experiment with fluent, an accurate simulation would be realized, regarding the flow patten in the system and equilibrium time to arrive the final state.