Time step was 1e-6 and i ran the calculation for 20 steps (2e-5 s). I changed to 1e-8 and then run it for ~1700 steps (1.7e-5 s). Volume fraction, stream function and velocity vector are shown below.nThe weird current did not happen on the interface so far, but the velocity field near the interface is quite strange and velocity there is quite big compared to the case without CSF.Thanks for your help, KarthiknBestnJianhuann