IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4A1_3E-O7

Room A1

Date/Time: July 24 10:15-10:30

A fast Eulerian multiphase flow model for the three-dimensional numerical simulation ofnon-equilibrium effects in turbulent volcanic plumes
Matteo Cerminara1 , Tomaso Esposti Ongaro2 , Maria Vittoria Salvetti3 , Luigi Carlo Berselli31

Scuola Normale Superiore, Italy, 2 Istituto Nazionale di Geofisica e Vulcanologia, Italy, 3 Universita’ diPisa, Italy
E-mail: matteo.cerminara@sns.it

We have developed a fast Eulerian model for the Large Eddy Simulation (LES) of turbulent volcanic plumes. The
model is based on the equilibrium-Eulerian approximation (Ferry and Balachandar, Int. J. Multiph. Flow 2001;
Cantero et al., J. Geophys. Res., 2008) for a polydisperse flow.
This approach gives particular attention to the particle grain size distribution and its interaction with the turbulence.
We are indeed particularly interested in the disequilibrium between the ash and the gaseous part of the volcanicmixture, our aim being to properly simulate phenomena like preferential concentration and plume entrainment.
In the limit of fine particles (at Stokes number < 0.2) and dilute regimes (particle volume concentration < 1.e-3), suchmethod allows to overcome the limitations of the pseudogas models (assuming a perfect kinematic and thermal
equilibrium between gas and particles - Oberhuber et al, J. Volcanol. Geoth. Res., 1998; Suzuki et al., J. Geophys.
Res., 2005) without entailing the complexity and computational cost of the fully coupled multiphase flow Eulerianmodels (Neri et al., J. Geophys. Res., 2003; Dufek and Bergantz, Theor. Comput. Fluid Dyn., 2007).
To model the non-linear coupling between turbulent scales and the effect of sub-grid turbulence on the large-scaledynamics, we have adopted the LES formalism (which is preferable in transient regimes) for compressible flows.
Our computational work is based on development and exploitation of these models into the numerical solvers ofOpenFOAM, which is one of the best known CFD open source parallel software packages.
Preliminary numerical benchmarks demonstrate that the model is able to capture important non-equilibrium
phenomena in gas-particle mixtures, such as particle clustering and ejection from large-eddy turbulent structures,
as well as compressibility and thermal effects.
A quantitative assessment of the reliability of Direct Numerical Simulation (DNS) and LES results with respect tomodeling approximations and numerical errors has been carried out by comparing numerical results to experimental
and computational studies of homogeneous, isotropic turbulence.
In such a simplified geometry, the numerical solver is able to accurately reproduce the turbulent spectrum and theKolmogorov energy cascade.
Preliminary three-dimensional numerical simulation of volcanic plume dynamics demonstrate that gas-particle
non-equilibrium phenomena have a significant impact on turbulent structures and can affect the entrainment rate
and the atmospheric dispersal of volcanic ash.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

868