Film formation in VOF model using fluent

Ajay

I want to model Slug flow in microchannel. I am using fluent for the same. I have a geometry of "T" type mixer with each phase coming from either arm of the "T". The out arm of the "T " is kept about 20 times the typical length of the slug bubble observed in the experiments.

Gas is considered as secondary where as liquid is considered as primary.

Boundary condition I have set is velocity inlet for the both the phases and pressure outlet for the outlet. To take into account the effect of surface tension I have specified a value of surface tension as .072 N/m and the contact angle of 120 on the tube wall (assuming a hydrophobic surface of the tube). wall is specified as no slip

I am using PISO for pressure velocity coupling and discretization scheme of PRESTO, Second order upwind and geo reconstruct scheme for Pressure, momentum and volume fraction respectively.

My main problem is I am not getting the film formation even after resolving the grid till 5 micron size near the wall boundary. Moreover I am getting discrete gas and liquid slugs moving one after another. Can anybody help me in locating what exactly is going wrong and why the film formation is not taking place

Thanks in advance

Greetings Ajay