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| Titel |
A semi-implicit, second-order-accurate numerical model for multiphase underexpanded volcanic jets |
| VerfasserIn |
S. Carcano, L. Bonaventura, T. Esposti Ongaro, A. Neri |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1991-959X
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| Digitales Dokument |
URL |
| Erschienen |
In: Geoscientific Model Development ; 6, no. 6 ; Nr. 6, no. 6 (2013-11-04), S.1905-1924 |
| Datensatznummer |
250085012
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| Publikation (Nr.) |
 copernicus.org/gmd-6-1905-2013.pdf |
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| Zusammenfassung |
| An improved version of the PDAC (Pyroclastic Dispersal Analysis
Code, Esposti Ongaro et al., 2007) numerical model for the
simulation of multiphase volcanic flows is presented and validated
for the simulation of multiphase volcanic jets in supersonic
regimes. The present version of PDAC includes second-order time- and
space discretizations and fully multidimensional advection
discretizations in order to reduce numerical diffusion and enhance
the accuracy of the original model. The model is tested on the
problem of jet decompression in both two and three dimensions. For
homogeneous jets, numerical results are consistent with experimental
results at the laboratory scale (Lewis and Carlson, 1964). For
nonequilibrium gas–particle jets, we consider monodisperse and
bidisperse mixtures, and we quantify nonequilibrium effects in terms
of the ratio between the particle relaxation time and
a characteristic jet timescale. For coarse particles and low
particle load, numerical simulations well reproduce laboratory
experiments and numerical simulations carried out with an
Eulerian–Lagrangian model (Sommerfeld, 1993). At the volcanic
scale, we consider steady-state conditions associated with the
development of Vulcanian and sub-Plinian eruptions. For the finest
particles produced in these regimes, we demonstrate that the solid
phase is in mechanical and thermal equilibrium with the gas phase
and that the jet decompression structure is well described by
a pseudogas model (Ogden et al., 2008). Coarse particles, on the other hand, display significant nonequilibrium effects, which associated
with their larger relaxation time. Deviations from the equilibrium regime, with maximum
velocity and temperature differences on the order of 150 m s−1
and 80 K across shock waves,
occur especially during the rapid acceleration phases, and are able
to modify substantially the jet dynamics with respect to the homogeneous case. |
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