Experimental and computational investigations to regulate the interfacial instabilities in confined geometries

Abstract

Fingering instabilities are ubiquitous in porous media flows like enhanced oil recovery, contaminant transport in aquifers to name a few. Fingering instabilities are observed when the fluid-fluid interface deforms into finger like patterns due to some variation in the physical property during the flow. The fingering instability arising due to change in viscosity, in particular, when a less viscous fluid displaces a more viscous one, is termed as viscous fingering (VF), while another kind of instability also arises due to a change in the permeability. We concentrate on radial displacements, where rectilinear also used to study this phenomenon. Viscous fingering can be seen in both miscible and immiscible fluids. The Hele-Shaw cell is one of them in which the transparent glass plates separated by small gap b is used to see the porous media dynamics [60] also to observe the viscous fingering instabilities. We discussed the whole experimental set-up with designing, fabrication and working procedure. We focus on understanding the mechanisms controlling the VF dynamics through finiteness. We attempt to achieve the same by merely modifying the initial conditions of radial displacement flow, that is, by considering a finite source. The effects of competition between convection and diffusion on the control ability of VF are parameterised in terms of the radius of the finite source and are explained through experiments. The gap width has a significant effect on VF dynamics. The goal is to experimentally map out a detailed phase diagram that demonstrates the trends and effects these parameters have on the fingering pattern. VF mechanisms like tip-splitting, merging and shielding can be overcome through this. The interfacial length across which mixing can occur changes over time, and understanding this is important in determining the mixing efficiency of a particular pattern. We find that it is more feasible to suppress viscous fingering in a radially Hele-Shaw cell than a uniform radial cell. We focus on understanding the mechanisms controlling the VF dynamics through finiteness. We explain the effect of three zones namely Diffusion-Convection-Diffusion (D-C-D) on VF dynamics. The competition between the two opposing forces in linear as well as non-linear regime by performing experiments. We attempt to achieve the same by merely modifying the initial conditions of radial displacement flow, that is, by considering a finite source. The effects of competition between convection and diffusion on the control ability of VF are parameterised in terms of the radius of the finite source and are explained through experiments. Optohydrodynamics instability concerned with the light induced instability on liquid interfaces. Microscopic surface deformation of fluid interfaces subjected to optical excitation is well studied, however, it is unknown how the geometries of Gaussian beam and fluid system affect nanoscale optohydrodynamics. Here, we show numerically how the interplay between geometries of a Gaussian beam and fluid-medium leads to an optimal enhancement of nanoscale opto-hydrodynamic deformation of airwater interface for a fixed radiation pressure force. The study is carried out through FEA with the help of COMSOL MultiphysicsRO 5.2a.[34] to measure the time dependent nanometre-scale deformation. Another investigation includes the liquid-liquid immiscible system and interface deformation under effect of the radiation pressure. This investigation contains a discussion of the nonlinear optical morphology that have been observed in the Bordeaux experiments [18, 20], and how this shape can be understood qualitatively from the COMSOL Multiphysics modelling. Here, We have shown the effects of radiation forces regulated through ω and variation with different Viscosity ratio (VR). We have controlled the deformation, manipulated its effects through ω and found the critical beam radius ωc and its correlation with VR. Due these VR the topography of interfacial deformation also changed.