Viscous modes in two-phase mixing layers

The temporal instability of parallel viscous two-phase mixing layers is studied by adopting a composite error function flow profile such that boundary layers in each fluid sandwich the interface. Linear spectra and neutral stability curves are calculated numerically and the effects of varying the density ratio, viscosity ratio and Weber number are presented. In addition to the interfacial mode two Tollmien-Schlichting type modes are found and attributed to the presence of the two viscous boundary layers. This is important because it is shown that any of these three modes may be the most unstable, depending on parameter values. Mode multiplicity and competition has not yet been thoroughly explored for this problem even though it is essential to the analysis of experiments and to further stability study of flows relevant to breaking up of interfaces. (C) 2002 American Institute of Physics.