Numerical investigation of large wave interactions on free falling films

From experimental measurements of a free falling liquid film at Re880, four representative large, evolving or interacting waves were selected for computational domains in which the Navier-Stokes equations were numerically solved. The algorithm computed velocity and pressure fields within each wave, as well as the shape necessary to match experimental wall shear stress data. Results show interaction effects significantly modify flow fields, compared to large solitary waves. Waves having two peaks had two closed recirculation regions, with a mixing layer separating them. The size of the recirculation regions was dependent on the extent of separation of the wave peaks. As with solitary waves, strong streamwise accelerations exist, with both location and magnitude varying with shape and evolutionary character of the wave. Heat and mass transfer rates must be enhanced by these flow properties, which are shown to have a complicated dependence on wave structure. Examination of the flow fields suggests parabolic streamwise velocity profiles are generally deficient, explaining shortcomings experienced by hydrodynamic models based on such simple velocity profiles.