Numerical Simulations of Turbulent Mixing in Eruption Clouds

Eruption clouds in explosive volcanic eruptions are a kind of free boundary shear flow with very high Reynolds numbers (Re > 10), and their dynamics are governed by entrainment of ambient air into eruption clouds by turbulent mixing. We developed a numerical pseudo-gas model of an eruption cloud by employing three-dimensional coordinates, a high-order accuracy scheme, and a fine grid size in order to investigate the behavior of entrainment due to turbulent mixing. Our results have revealed that the efficiency of turbulent mixing no longer depends on the Reynolds number when the turbulence is fully developed. Our model has successfully reproduced the features of turbulent mixing at high Reynolds numbers as well as fundamental features of the dynamics of eruption clouds, such as the generation of eruption columns and/or pyroclastic flows.