two phase slug flow

Justion

I am simulating slug flow through a horizontal large diameter 0.08 m, pipe length is 15m, I have adpoted the VOF model with a 0.0737 constant surface tension. turbulence model.

BC: I split inlet to gas inlet and water inlet to set inlet velocity and hydraulic diameter respectively. Gas: 5 m/s 0.064m Liquid:2.5m/s 0.016m

BC for outlet is outflow.

IC: I set gas and liquid stratified flow.

12000 cells.

From the flow pattern map, the transition from stratified to slug flow should be seen from the result.But from my result ,it is always stratified wavy flow.

Anyone can give me some ideas.

Sincerely appreciate your kind assistance. Thanks in advance.