Secondary Flows in stratified wavy flow
 

I have a graduate student we work together with Stratified wavy two phase flow within a pipe. We aimed from our study to study secondary flows which generating from the wavy interface. We use ANSYS FLUENT 12 currently we have a difficulty to define the wavy interface within FLUENT we use some attempts with using two separating inlets but we failed to get the secondary flow case? May somebody guide us to how we can define the interface and its roughness (which equal to 2.3 * liquid height) within the code?

REGARDS
kbaker