Satyajit Pramanik — Page 2

arXiv2015

Viscosity scaling of fingering instability in finite slices with Korteweg stress

We perform linear stability analyses (LSA) and direct numerical simulations (DNS) to investigate the influence of the dynamic viscosity on viscous fingering (VF) instability in miscible slices. Selecting the characteristic scales appropriately the importance of the magnitude of the dynamic viscosity of individual fluids on VF in miscible slice has been shown in the context of the transient interfacial tension. Further, we have confirmed this result for immiscible fluids and manifest the similarities between VF in immiscible and miscible slices with transient interfacial tension. In a more general setting, the findings of this letter will be very useful for multiphase viscous flow, in which the momentum balance equation contains an additional stress term free from the dynamic viscosity.

physics.flu-dyn↗

arXiv2014

Effect of Péclet number on miscible rectilinear displacement in a Hele-Shaw cell

Influence of fluid dispersion on the Saffman-Taylor instability in miscible fluids has been investigated both in the linear and nonlinear regimes. The convective characteristic scales are used for the dimensionless formulation that incorporates Péclet number (Pe) into the governing equations as a measure for the fluid dispersion. A linear stability analysis (LSA) has been performed in a similarity transformation domain using the quasi-steady-state approximation. LSA results show that systems with large Pe become more unstable and the onset of instability occurs earlier compared to the case when Pe is smaller. Variations of the most unstable wave number and the cut-off wave number with Pe have been analyzed. Fourier spectral method has been used for the numerical simulations of the fully nonlinear system. The results indicate that the wave numbers of the unstable modes increase with Pe. Influence of the anisotropic dispersion on the onset in both the linear and nonlinear regimes has been analyzed. Large transverse diffusivity increases the length scale of the fingers quickly and merges the fingers to generate coarser fingers. Finally the combined effect of the Korteweg stress and Pe in the linear regime has been perused. In the presence of the Korteweg stresses and depending upon various flow parameters, a fluid system with larger Pe exhibits smaller instantaneous growth rate than with smaller Pe, which is a counter-intuitive result.

physics.flu-dyn↗