3D Simulations of a Pyroclastic Surge as an Example of a Compressible Suspension Flow(<Special Issue>CIP)

This paper demonstrates the usefulness of the CIP-combined unified procedure (C-CUP) to perform numerical simulations of a compressible flow of a suspension. As a conspicuous example of such a flow, we present three-dimensional numerical simulations of a pyroclastic surge, which spreads laterally over the ground surface during some volcanic eruptions as occurred at Unzen Volcano in 1991-1995. Since a pyroclastic surge suspends numerous solid particles, the density of a pyroclastic surge cannot be approximated by the equation of state for an ideal gas. On the other hand, a pyroclastic surge greatly changes its density as it heats and expands the air mixed from the calm surroundings. The above characteristics bring unique features into the motion of a pyroclastic surge. The features are successfully simulated by C-CUP with a slight modification owing to the fact that C-CUP can incorporate the equation of state of an arbitrary form.