Surface wave dynamics of falling film on the surface of periodic rectangular wall under monochromatic-frequency flowrate forcing disturbances is studied via numerical simulation. Waveforms formed on the periodic rectangular wall are different from those on the flat plate. At low frequency, the perturbation introduced at the inlet first undergoes a steady flow region and then develops into solitary waves. When the frequency becomes higher, solitary waves disappear. Film deformations in the steady flow region and characteristics of solitary waves are studied as the film travels down. There are circulations at the depression of periodic wall which are dependent on the local film characteristics and geometry of the corrugation. Moreover, the flow rate and geometry of the corrugations can also affect the evolvement of the monochromatic perturbation.
The objective of this study is to investigate numerically the flow characteristics of falling film on horizontal circular tubes. Numerical simulations are performed using FLUENT for 2D configurations with one and two cylinders. The volume of fluid method is used to track the motion of liquid falling film and the gas-liquid interface. The effect of flow characteristics on heat and transfer coefficient may be remarkable, although it has been neglected in previous studies. The velocity distribution and the film thickness characteristics on the top tube, some special flow characteristics on the bottom tube, intertube flow modes and effect of liquid feeder height on flow characteristics have been studied. Our simulations indicate that 1） the velocity distributions of the upper and lower parts of the tube are not strictly symmetric and non- uniform, 2） the film thickness depends on flow rate and angular distributions, 3） the flow characteristics of the top tube are different from those of the bottom tube, 4） three principal and two intermediate transition modes are distinguished, and 5） the liquid feed height plays an important role on the formation of falling film. The numerical results are in a good agreement with the theoretical values by the Nusselt model and the reported results.
