Turbulence diffusion effects at material interfaces, with application to the Rayleigh-Taylor instability

A new set-up is proposed to numerically investigate turbulent multi-material mixing in the presence and in the absence of a gravitational field. The set-up consists of an initial unperturbed interface that separates two fluids in an existing isotropic velocity field. The initial unperturbed interface evolves into a turbulent multi-material mixing region due to the fluctuating velocity field. For simulations without gravity, the initial velocity field decays, while the simulations with gravity are Rayleigh-Taylor unstable, such that the misalignment of the pressure and the density gradients generates baroclinic vorticity feeding the instability. The flow parameters are chosen such that the density fields are different, but that the kinetic energy decays at the same rate in both fluids. Direct numerical simulations are performed using a high-order accurate minimally dissipative kinetic-energy preserving and interface-capturing scheme. Results with and without gravity are compared to investigate flow isotropy and intermittency. The current results suggest that the initial anisotropy in the composition is not sufficient to make the initial isotropic field anisotropic in the absence of gravity.