Non-modal stability analysis of stratified two-phase channel flows. (February 2019)

• Record Type: Journal Article
• Authors: Barmak, I.; Gelfgat, A.Yu.; Ullmann, A.; Brauner, N.
• Is Part Of: International journal of multiphase flow. Volume 111(2019)
• Page Start: 122
• Page End: 139
• Publication Date: 2019-02
• Subjects: Two-phase stratified flow -- Non-modal stability -- Transient energy growth -- Optimal perturbations -- Gravity effect; Multiphase flow -- Periodicals; Écoulement polyphasique -- Périodiques; Multiphase flow; Periodicals; 620.1064
• DOI: 10.1016/j.ijmultiphaseflow.2018.10.020
• Languages: English
• ISSNs: 0301-9322

Abstract

Highlights: Transient energy growth of perturbations in stratified two-phase flow is studied. The energy norm should account for the kinetic, interfacial and gravitational energy. The maximal transient energy growth is attained mostly by spanwise perturbations. Oblique optimal perturbations can yield noticeable interface deformation. Non-modal growth may be a precursor to subcritical flow pattern transition. Abstract: The non-modal transient growth of perturbations in horizontal and inclined channel flows of two immiscible fluids is studied. 3D perturbations are examined in order to find the optimal perturbations that attain the maximum amplification of perturbation energy at relatively short times. Definition of the energy norm is extended to account for the gravitational potential energy along with the kinetic energy and the interfacial capillary energy. Contrarily to the fastest exponential growth, which is reached by essentially 2D perturbations, the maximal non-modal energy growth is attained mostly by three-dimensional spanwise perturbations. Significant transient energy growth is found to occur in linearly stable flow configurations, which, similarly to single phase shear flows, may trigger non-linear destabilizing mechanisms within one of the phases. It is shown that the transient energy growth in linearly stable cases can be accompanied by noticeable interface deformations. Therefore, flow pattern transition due to non-modal transient growth and reduction of the range of operational conditions for which stratified-smooth flow remains stable cannot be ruled out.