Interaction between pyroclastic density currents and buildings: Numerical simulation and first experiments

The interaction between pyroclastic density currents and buildings is investigated by means of numerical simulation and large-scale experiments. Numerical simulation is performed with the Euler-Lagrange approach using a two-way coupling between gas and particles of three sizes. The collapse of an eruptive column consisting of a mixture of gas and pyroclasts is produced experimentally, and the impact of the resulting shear current with mock-ups representing buildings is monitored. A combination of results from simulations and experiments shows that, upon impact with a building, the multiphase current develops strong turbulence intensity, which significantly affects particle dispersion. The flow recirculation around the building induces forced deposition at the front and wake in the back wall, with flow reattachment farther away. These changes produce a variation in the dynamic pressure, which is the most important parameter for assessing the impact of pyroclastic density currents moving over inhabited areas.