[akchetty]

Hello,

I have been trying to perform vertical air-glycerol slug flow simulations in Fluent using VOF and was thinking if anyone can help or give an advice regarding the issue I am facing right now. The terminal velocity I am getting for a rising taylor bubble in stagnant glycerol solution is only half of what it is supposed to be according to literature and other CFD results in the paper (Numerical Study of Hydrodynamic Characteristics of Gas–Liquid Slug Flow in Vertical Pipes etc). I tried following the methodology people have used in the literature, the one of solving the two-phase set up in a frame moving with the Taylor bubble. So I have the two walls moving downwards (2-D domain ) along with the liquid (top- velocity inlet and bottom - outflow) at terminal velocity of the taylor bubble (say 0.14 m/s). Unless I use a velocity value almost half of the correct value from literature, my Taylor bubble either moves up or down the domain. The bubble should remain stationary if the walls are moving with correct velocities which is the terminal velocity of the bubble. I tried using stationary domain but still I am having the same problem of half the terminal velocity. I am using pipe diameters of 19-22 mm and mesh sizes of 1-0.5 mm and initially start with a film thickness calculated from empirical correlations and start with a bubble length of 3.5 times the bubble diameter. My solution converges, but terminal velocities are off by half. Any idea or suggestion regarding where I may be doing a mistake ? Looking forward to your reply. Thank you.