[Zaki Zam]

I'm working on CFDs from Core Annular Flow. Oil is designed to flow in the core and water will be annular. I use the VOF model and the k-e turbulent, then I set oil as primary phase, water as secondary. The oil inlet is in the small pipe section and the water inlet is in the big pipe.

The problem is why the flow fails, the fluid flow is dominated by oil along the pipe and water is only found at the inlet and outlet ends?

The attached images are Pipe Meshing, Oil Vol. Fraction, and Water Vol. Fraction

[vinerm]

VOF has no distinction of primary and secondary when it comes to VOF; they are all treated same, except that the volume fraction equation is not solved for the primary.

It all boils down to correct specification of

1. Boundary Conditions
2. Physical Models
3. Operating Conditions

CAF requires rather delicate balance of the forces and may not exist without the generation of the waves between the two phases. Therefore, gravity and the flow rates are very important to maintain a CAF. Check for gravity (value and direction), operating pressure, location of the operating pressure, operating density (should be the value of the density of the oil).