KELVIN-HELMHOLTZ STABILITY-CRITERIA FOR STRATIFIED FLOW - VISCOUS VERSUS NON-VISCOUS (INVISCID) APPROACHES

The neutral stability lines obtained from the viscous Kelvin-Helmholtz analysis and the inviscid analysis are quite different for the case of low liquid viscosities, whereas they are quite similar for high viscosity, contrary to what one would expect. This puzzling result is considered in this work. It is shown that the stability behavior regarding the amplification rate is actually almost the same for the two analyses for a wide range of liquid viscosities and for various pipe inclinations. The results obtained in the present work also support Barnea's interpretation of the viscous and inviscid analyses as a means for predicting various transitions from stratified flow.