Mutation during displacement

[xiangWu-WW]

Hello, Dr. Yang. I am new to CFD, I am doing two-phase flow displacement, I built a 64^3 model, apply the driving force in the left side of the X direction, the displacement was slow for the first 75,000 times, by 80,000 times it was all through, They are 5,000, 20,000, 40,000, 75,000 and 80,000 times respectively，what is the cause of this? The all iterations is 100000. In addition, the phase_ftb64.dat file is all set to 1, and the fixed phase boundary condition is used. Then, does the parameter setting of niu_g represent -1 is the phase of displacement force, and does psi_solid represent the contact Angle of niu_g phase between niu_l and the solid skeleton surface? Looking forward to your reply.