Onset of fingering instability in a finite slice of adsorbed solute

TL;DR

This paper investigates how linear adsorption affects the initiation of fingering instability in miscible displacement, providing a more accurate early-time analysis and revealing a non-monotonic relationship with the retention parameter.

Contribution

It introduces a generic linear stability analysis that captures early diffusion-dominated regimes and improves onset predictions over quasi-steady state methods.

Findings

Onset time depends non-monotonically on the retention parameter.

The linear stability analysis aligns with nonlinear simulation results.

The method aids in characterizing linear and nonlinear regimes of instability.

Abstract

The effect of a linear adsorption isotherm on the onset of fingering instability in a miscible displacement in the application of liquid chromatography, pollutant contamination in aquifers etc. is investigated. Such fingering instability on the solute dynamics arise due to the miscible viscus fingering (VF) between the displacing fluid and sample solvent. We use a Fourier pseudo-spectral method to solve the initial value problem appeared in the linear stability analysis. The present linear stability analysis is of generic type and it captures the early time diffusion dominated region which was never expressible through the quasi-steady state analysis (QSSA). In addition, it measures the onset of instability more accurately than the QSSA methods. It is shown that the onset time depends non-monotonically on the retention parameter of the solute adsorption. This qualitative influence of the retention parameter on the onset of instability resemblances with the results obtained from direct numerical simulations of the nonlinear equations. Moreover, the present linear stability method helps for an appropriate characterisation of the linear and the nonlinear regimes of miscible VF instability and also can be useful for the fluid flow problems with the unsteady base-state.