Double Diffusive Instability in a Thin Vertical Channel

In highly confined environments, single constituent Rayleigh-Taylor instabilities are suppressed. In this talk we will demonstrate that double-diffusive instabilities persist in highly confined environments while, in the absence of differential diffusion, instabilities such as the single constituent Rayleigh-Taylor instabilities cannot form.

We will present direct numerical simulations of double-diffusive instabilities in the finger regime with domain widths of 1-4mm. Using these results, we will show that double-diffusive instabilities demonstrate complex time-dependent evolution down to lateral extents of 1.25mm. This implies that differential diffusion may be significant in driving localized mixing within porous media with large pore spaces. We will discuss the energetics, horizontal asymmetry and buoyancy flux due to the instability and utilize these results to characterize the instability within domain-dependent regimes. Further, we will demonstrate that instabilities associated with wider domains are well-characterized by a time-dependent Grashof number which quantifies the ratio of diffusive effects to buoyancy forces.

Time permitting, we will discuss the impact of side wall topography on the double diffusive instabilities.