Stratified-smooth zone

For the sake of clarity, the focus in Figure 18 is on the interplay and practical relevance of the stability boundaries (ZNS or ZNS) and the L-T laminar/turbulent flow regime transitional line in predicting the stratified-smooth/wavy flow pattern transition. Other transitional boundaries, which confine the stratified-smooth and stratified-wavy zones, are shown in Figure 19. For relatively low gas rates, the stratified-smooth zone is bounded by the slug or bubbly patterns while the stratified-wavy zone, at high gas rates, is bounded by the transition to annular pattern. 

It is shown by Brauner and Moalem Maron [40,45] that, indeed, the wavy-stratified regime is confined to a domain at whose boundaries the two-fluid formulation becomes ill-posed. The ill-posedness boundary is always located in the region of amplified waves since the stable smooth stratified zone, which is confined by the stability boundary, is always a sub-zone of the well-posed region [43-45],... 

The general implication of the stability boundary (ZNS or ZNS ) and the well-posedness boundary (ZRC) is in defining three zones the area within the stability boundary is well-understood to be the stable smooth stratified zone. Beyond the ZRC boundary, the complex characteristics indicate that the governing equations of the stratified flow configuration are ill-posed with respect to long wave modes in the wave spectra. In this sense, the ZRC boundary represents an upper bound... 

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