Projects per year
Abstract
We consider the genesis and dynamics of interfacial instability in gasliquid flows, using as a model the twodimensional channel flow of a thin falling film sheared by countercurrent gas. The methodology is linear stability theory (OrrSommerfeld analysis) together with direct numerical simulation of the twophase flow in the case of nonlinear disturbances. We investigate the influence of three main flow parameters (density contrast between liquid and gas, film thickness, pressure drop applied to drive the gas stream) on the interfacial dynamics. Energy budget analyses based on the OrrSommerfeld theory reveal various coexisting unstable modes (interfacial, shear, internal) in the case of high density contrasts, which results in mode coalescence and mode competition, but only one dynamically relevant unstable internal mode for low density contrast. The same linear stability approach provides a quantitative prediction for the onset of (partial) liquid flow reversal in terms of the gas and liquid flow rates. A study of absolute and convective instability for low density contrast shows that the system is absolutely unstable for all but two narrow regions of the investigated parameter space. Direct numerical simulations of the same system (low density contrast) show that linear theory holds up remarkably well upon the onset of largeamplitude waves as well as the existence of weakly nonlinear waves. In comparison, for high density contrasts corresponding more closely to an airwatertype system, although the linear stability theory is successful at determining the mostdominant features in the interfacial wave dynamics at earlytointermediate times, the short waves selected by the linear theory undergo secondary instability and the wave train is no longer regular but rather exhibits chaotic dynamics and eventually, wave overturning.
Original language  English 

Article number  042102 
Journal  Physics of Fluids 
Volume  28 
Issue number  4 
DOIs  
Publication status  Published  1 Apr 2016 
Keywords
 physics.fludyn
Fingerprint Dive into the research topics of 'Linear and nonlinear instability in vertical countercurrent laminar gasliquid flows'. Together they form a unique fingerprint.
Projects
 2 Finished
Profiles

Prashant Valluri
 School of Engineering  Personal Chair in Fluid Dynamics
Person: Academic: Research Active