We offer new insights and results on the hydrodynamics of solitary waves on inertiadominated
falling liquid films using a combination of experimental measurements,
direct numerical simulations (DNS) and low-dimensional (LD) modelling. The DNS
are shown to be in very good agreement with experimental measurements in terms
of the main wave characteristics and velocity profiles over the entire range of
investigated Reynolds numbers. And, surprisingly, the LD model is found to predict
accurately the film height even for inertia-dominated films with high Reynolds
numbers. Based on a detailed analysis of the flow field within the liquid film, the
hydrodynamic mechanism responsible for a constant, or even reducing, maximum
film height when the Reynolds number increases above a critical value is identified,
and reasons why no flow reversal is observed underneath the wave trough above a
critical Reynolds number are proposed. The saturation of the maximum film height
is shown to be linked to a reduced effective inertia acting on the solitary waves as
a result of flow recirculation in the main wave hump and in the moving frame of
reference. Nevertheless, the velocity profile at the crest of the solitary waves remains
parabolic and self-similar even after the onset of flow recirculation. The upper limit
of the Reynolds number with respect to flow reversal is primarily the result of
steeper solitary waves at high Reynolds numbers, which leads to larger streamwise
pressure gradients that counter flow reversal. Our results should be of interest in the
optimisation of the heat and mass transport characteristics of falling liquid films and
can also serve as a benchmark for future model development.