WAVE FORMATION IN THE GRAVITY-DRIVEN LOW-REYNOLDS-NUMBER FLOW OF 2 LIQUID-FILMS DOWN AN INCLINED PLANE

Wave formation in the gravity-driven low-Reynolds number flow of two l iquid films down an inclined plane is studied by a linear stability an alysis. Wavy motion can appear due to an instability of either the flu id-fluid interface or the fluid-air free surface. It is shown that the flow is always unstable and wavy motion can occur when the less visco us layer is in the region next to the wall for any Reynolds number and any finite interface and surface tensions. Stability can be achieved for the configuration with the more viscous component adjacent to the wall in the presence of interfacial tension when Reynolds number is sm all enough.