Browsing by Author "Mishra, Manoranjan"

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A numerical study on reaction-induced radial fingering instability
(2019-01-11)
Sharma, Vandita
;
Pramanik, Satyajit
;
Chen, Ching-Yao
;
Mishra, Manoranjan
;
機械工程學系
The dynamics of A + B -> C fronts is analysed numerically in a radial geometry. We are interested to understand miscible fingering instabilities when the simple chemical reaction changes the viscosity of the fluid locally and a non-monotonic viscosity profile with a global maximum or minimum is formed. We consider viscosity-matched reactants A and B generating a product C having different viscosity than the reactants. Depending on the effect of C on the viscosity relative to the reactants, different viscous fingering (VF) patterns are captured which are in good qualitative agreement with the existing radial experiments. We have found that, for a given chemical reaction rate, an unfavourable viscosity contrast is not always sufficient to trigger the instability. For every fixed Peclet number (Pe), these effects of chemical reaction on VF are summarized in the Damkohler number (Da) - the log-mobility ratio (R-c) parameter space that exhibits a stable region separating two unstable regions corresponding to the cases of more and less viscous product. Fixing Pe, we determine Da-dependent critical log-mobility ratios R-c(+) and R-c(-) such that no VF is observable whenever R-c(-) <= R-c <= R-c(+). The effect of geometry is observable on the onset of instability, where we obtain significant differences from existing results in the rectilinear geometry.
Control of radial miscible viscous fingering
(2020-02-10)
Sharma, Vandita
;
Nand, Sada
;
Pramanik, Satyajit
;
Chen, Ching-Yao
;
Mishra, Manoranjan
We investigate the stability of radial viscous fingering (VF) in miscible fluids. We show that the instability is determined by an interplay between advection and diffusion during the initial stages of flow. Using linear stability analysis and nonlinear simulations, we demonstrate that this competition is a function of the radius r0 of the circular region initially occupied by the less-viscous fluid in the porous medium. For each r0, we further determine the stability in terms of Peclet number (Pe) and log-mobility ratio (M). The Pe-M parameter space is divided into stable and unstable zones: the boundary between the two zones is well approximated by Mc Dff.r0 /Pe 0:55 c. In the unstable zone, the instability is reduced with an increase in r0. Thus, a natural control measure for miscible radial VF in terms of r0 is established. Finally, the results are validated by performing experiments that provide good qualitative agreement with our numerical study. Implications for observations in oil recovery and other fingering instabilities are discussed.