Bubble grows in duct(2D)
 

i am trying to simulating bubble growth precess in minichannel. because i am a new user on Fluent,i think maybe it is more feasibel and economic for me to use the tutorial case included in Fluent. So i exchange the materials(water to air, air to water) in the Tuorial Guide 18 'Using the VOF Model' which is simulating `the ink injet into air chamber` problem originally (maybe all of u are familiar with it). And changed the walls to hydrophilic.

Unfortunately,the result is not like what i assumed i.e. the bubble can not grow up smoothly and splited as shown in attached files(the oringinal condition after pathing the ink chamber wiht air was also attached). i am confused with the reason:confused:
Is there anyboday who can give me some help?

thanks in advance