Spanwise structuring and rivulet formation in suspended falling liquid films

In thin films flowing down the underside of an inclined planar substrate, surface topology is known to evolve towards a spanwise structuring of rivulets. While experiments imply a connection between long-term spanwise structuring and primary instabilities (PI) of the film surface at low Reynolds number (Re), this connection is not conclusive if a larger parameter space of Re and Kapitza number (Ka) is considered. Using an integral boundary layer model for falling liquid films and varying imposed initial conditions, Re, Ka, and wall inclination, we numerically investigate long-term rivulet evolution and its connection to PI, obtaining excellent concordance with previous experimental data.