simulation of taylor bubble
 

Hi, I'm traying to simulate the motion of a single taylor bubble rising in stagnant liquid in vertical tube with code SURFER 2D. in applying the boundary conditions, like this: 1)velocity gradients equals zero at the inlet and the outlet; 2)symmetry in the center; 3) no-slip condition at the wall. I find that the code is not very stable and I can't obtain the forme of the bubble. If one can help me how to implement the various boundary conditions in the SURFER code and also if there is any help to do this work. thanks.