ASHEE-1.0: a compressible, equilibrium–Eulerian model for volcanic ash plumes

Abstract

Abstract.A new fluid-dynamic model is developed to numerically simulate the non-equilibrium dynamics of polydisperse gas-particle mixtures forming volcanic plumes. Starting from the three-dimensional N-phase Eulerian transport equations for a mixture of gases and solid dispersed particles, we adopt an asymptotic expansion strategy to derive a compressible version of the first-order non-equilibrium model, valid for low-concentration regimes (particle volume fraction less than 10 −3 ) and particle Stokes number (St -i.e., the ratio between relaxation time and flow characteristic time) not exceeding about 0.2. The new model, which is called ASHEE (ASH Equilibrium Eulerian), is significantly faster than the N-phase Eulerian model while retaining the capability to describe gas-particle non-equilibrium effects. Direct Numerical Simulation accurately reproduces the dynamics of isotropic, compressible turbulence in subsonic regimes. For gas-particle mixtures, it describes the main features of density fluctuations and the preferential concentration and clustering of particles by turbulence, thus verifying the model reliability and suitability for the numerical simulation of highReynolds number and high-temperature regimes in the presence of a dispersed phase. On the other hand, Large-Eddy Numerical Simulations of forced plumes are able to reproduce the averaged and instantaneous flow properties. In particular, the self-similar Gaussian radial profile and the development of large-scale coherent structures are reproduced, including the rate of turbulent mixing and entrainment of atmospheric air. Application to the Large-Eddy Simulation of the injection of the eruptive mixture in a stratified atmosphere describes some of the important features of turbulent volcanic plumes, including air entrainment, buoyancy reversal and maximum plume height. For very fine particles (St → 0, when non-equilibrium effects are negligible) the model reduces to the so-called dusty-gas model. However, coarse particles partially decouple from the gas phase within eddies (thus modifying the turbulent structure) and preferentially concentrate at the eddy periphery, eventually being lost from the plume margins due to the concurrent effect of gravity. By these mechanisms, gas-particle non-equilibrium processes are able to influence the large-scale behavior of volcanic plumes.

Impacts of Climate Change on Volcanic Stratospheric Injections: Comparison of 1‐D and 3‐D Plume Model Projections

“…On the other hand, three-dimensional (3-D) plume models resolve the multiphase Navier Stokes equations and turbulence down to grid scale (large eddy simulations). Some of them need an empirical parameter for the subgrid turbulence (Smagorinsky, 1963); others use dynamic large eddy simulations and do not need any parameters (Bardina et al, 1980;Cerminara, Ongaro & Berselli, 2016;Cerminara, Ongaro & Neri, 2016;Moin et al, 1991). These different approaches are the main cause of differences in plume height predictions among 3-D and 1-D models (Costa et al, 2016).…”

“…In particular, how would the feedback hypothesis of Aubry et al (2016)-decreased stratospheric volcanic inputs in a warmer world-be modified if investigated with a 3-D plume model? To answer these questions, we conduct a suite of benchmark numerical experiments to compare the projections of the 1-D plume model used by Aubry et al (2016) with a 3-D plume model (Cerminara, Ongaro & Berselli, 2016;Cerminara, Ongaro & Neri, 2016). In addition to refining predictions for the fate of volcanic plume dynamics on a warming Earth, our results provide valuable insights on differences between 1-D and 3-D plume models.…”

A New One‐Equation Model of Fluid Drag for Irregularly Shaped Particles Valid Over a Wide Range of Reynolds Number

“…In volcanology and Earth sciences in general, the shape-dependent aerodynamic drag is crucial in controlling the transport and deposition of nonspherical solid particles in dust storms (e.g., Doronzo et al, 2015;Kok et al, 2012), rivers and lakes (e.g., DIOGUARDI ET AL. AERODYNAMIC DRAG OF IRREGULAR PARTICLES 144 Zhu et al, 2017), pyroclastic flows (e.g., Dellino et al, 2008;, eruptive columns (e.g., Cerminara et al, 2016;Folch et al, 2016), and distal ash clouds (e.g., Beckett et al, 2015;Bonadonna et al, 2012;Bonasia et al, 2010;Costa et al, 2012Costa et al, , 2006). Therefore, a major effort has been posed to find reliable shapedependent drag laws that work on the widest possible range of fluid dynamic regimes quantified by Re (Alfano et al, 2011;Bagheri & Bonadonna, 2016;Chhabra et al, 1999;Chien, 1994;Dellino et al, 2005;Dioguardi et al, 2017;Dioguardi & Mele, 2015;Ganser, 1993;Haider & Levenspiel, 1989;Hölzer & Sommerfeld, 2008;Loth, 2008;Pfeiffer et al, 2005;Swamee & Ojha, 1991;Tran-Cong et al, 2004;Wilson & Huang, 1979).…”

Investigating Source Conditions and Controlling Parameters of Explosive Eruptions: Some Experimental-Observational- Modelling Case Studies

“…Plumeria: Mastin [6]; PlumeRise: Woodhouse et al [49]; PlumeMom: de' Michieli Vitturi [53]), and 3D models, which account for more complex interactions between the rising plume and the atmosphere (e.g. ATHAM: Herzog et al [54]; ASHEE: Cerminara et al [55]). One-dimensional models are often used in an operational sense in the event of an eruption because they are quick to employ and, due to the simplicity of the models they require less detailed knowledge of, for example, atmospheric conditions.…”