Solid Earth Discussions www.solid-earth-discuss.net 1869-9537 4 1 2012 10.5194/sed-4-173-2012 http://www.solid-earth-discuss.net/4/173/2012/ http://www.solid-earth-discuss.net/4/173/2012/sed-4-173-2012.html http://www.solid-earth-discuss.net/4/173/2012/sed-4-173-2012.pdf 173 202 2012-01-26 New developments in the analysis of volcanic pyroclastic density currents through numerical simulations of multiphase flows S. Lepore simone.lepore@unina.it C. Scarpati Dipartimento di Scienze della Terra, University of Naples Federico II, Largo San Marcellino 10, 80138 – Naples, Italy A granular multiphase model has been used to evaluate the action of differently sized particles on the dynamics of fountains and associated pyroclastic density currents. The model takes into account the overall disequilibrium conditions between a gas phase and several solid phases, each characterized by its own physical properties. The dynamics of the granular flows has been simulated by adopting a Reynolds Average Navier-Stokes model for describing the turbulence effects. Numerical simulations have been carried out by using different values for the eruptive column temperature at the vent, solid particles frictional concentration, turbulent kinetic energy, and dissipation. The results obtained underline the importance of the multiphase nature of the model and characterize several disequilibrium effects. The low concentration (≤ 5 · 10^–4) sectors lie in the upper part of the granular flow, above the fountain, and above the pyroclastic current tail and body as thermal plumes. The high concentration sectors, on the contrary, form the fountain and remain along the ground of the granular flow. Hence, pyroclastic density currents are assimilated to granular flows constituted by a low concentration suspension flowing above a high concentration basal layer (boundary layer), from the proximal regions to the distal ones. Interactions among solid, differently sized particles in the boundary layer of the granular flow are controlled by collisions between particles, whereas particles dispersal in the suspension is determined by the dragging of the gas phase. The simulations describe well the dynamics of a tractive boundary layer leading to the formation of stratified facies during eruptions having a different magnitude. Besnard, D. C. and Harlow, F. H.: Turbulence in multiphase flow, Int. J. Multiphas. Flow, 14, 679–699, 1998. Boyle, E. J., Sams, W. N. and Cho, S. M.: MFIX validation studies: December 1994 to January 1995, U.S. Dep. of Energy, Washington, D. C., 1998. Branney, M. and Kokelaar, P.: Pyroclastic density currents and the sedimentation of ignimbrites, Geol. Soc. Mem., 27, 143, 2002. Brey, J. J., Dufty, J. W., and Santos, A.: Kinetic models for granular flow, J. Stat. Phys., 97, 281–322, 1999. Burgisser, A. and Bergantz, G. W.: Reconciling pyroclastic flow and surge: the multiphase physics of pyroclastic density currents, Earth Planet. Sci. Lett., 202, 405–418, 2002. Chough, S. K. and Sohn, Y. K.: Depositional mechanics and sequence of a base surge, Songaksan tuff ring, Cheju Island, Korea, Sedimentology, 37, 1115–1135, 1990. Cole, P. D. and Scarpati, C.: A facies interpretation of the eruption and emplacement mechanisms of the upper part of the Neapolitan Yellow Tuff, Campi Flegrei, southern Italy, Bull. Volcanol., 55, 311–326, 1993. Cole, P. D, Perrotta, A., and Scarpati, C.: The volcanic history of the south-western part of the city of Naples, Geol. Mag., 131, 785–799, 1994. Crowe, C. T., Troutt, T. R., and Chung J. N.: Numerical models for two-phase turbulent flows, Annu. Rev. Fluid. Mech., 28, 11–43, 1996. Crowe, C., Sommerfeld, M., and Tsuji, Y.: Multiphase Flows With Droplets and Particles, CRC Press, Boca Raton, Fla., 1998. Dartevelle, S., Numerical modelling of geophysical granular flows: 1. A comprehensive approach to granular rheologies and geophysical multiphase flows, Geochem. Geophys. Geosyst., 5, 1–28, 2004. Dartevelle, S.: Comprehensive Approaches to Multiphase Flows in Geophysics: application to nonisothermal, non-homogenous, unsteady, large-scale, turbulent dusty clouds. I. Basic RANS and LES Navier-Stokes equations, LA-14228, Los Alamos Natl. Lab., Los Alamos, New Mexico, 51, 2005 Dartevelle, S. and Valentine, G.: Transient multiphase processes during the explosive eruption of basalt through a geothermal borehole (Námafjall, Iceland, 1977) and implications for natural volcanic flows, Earth Planet. Sci. Lett., 262, 363–384, 2007. Dartevelle, S., Rose, W. I., Stix, J., Kelfoun, K., and Vallance, J. W.: Numerical modelling of geophysical granular flows: 2. Computer Simulations of Plinian Clouds and Pyroclastic Flows and Surges, 5, 1–36, 2004. Dobran, F., Neri, A., and Macedonio G.: Numerical simulation of collapsing volcanic columns, J Geophys. Res., 98, 4231–4259, 1993. Druitt, T. H.: Pyroclastic density currents, in The Physics of Explosive Volcanic Eruptions, edited by: Gilbert, J. S. and Sparks, R. S. J., Geol. Soc. Spec. Publ., 145, 27–50, 1998. Ferziger, J. and Peri\'c, M.: Computational Methods for fluid dynamics, Springer, 423, 2002. Gidaspow, D.: Multiphase Flow and Fluidization: Continuum and Kinetic Theory Descriptions, Academic, San Diego, Calif., 467, 1994. Giordano, G., Porreca M., Musacchio, P., and Mattei, M: The Holocene Secche di Lazzaro phreatomagmatic succession (Stromboli, Italy): evidence of pyroclastic density current origin deduced by facies analysis and AMS flow directions, Bull. Volcanol., 70, 1221–1236, 2008. Gunn, D. J.: Transfer of heat or mass to particles in fixed and fluidized beds, Int. J. Heat Mass Transfer, 21, 467–476, 1978. Hoffmann, K. and Chiang, S.: Computational fluid dynamics, Engineering Education System, 2000. Kashiwa, B. A. and VanderHeyden, W. B.: Toward a general theory for multiphase turbulence. Part I. Development and gauging of the model equations, LA-13773-MS, Los Alamos Natl. Lab., Los Alamos, New Mexico, 88, 2000. Lakehal, D.: On the modelling of multiphase turbulent flows for environmental and hydrodynamic applications, Int. J. Multiphase Flow, 28, 823–863, 2002. Leith, C. E.: Stochastic backscatter formulation for three-dimensional compressible flow, in Large Eddy Simulation of Complex Engineering and Geophysical Flows, edited by: Galperin, B. and Orszag, S. A., Cambridge Univ. Press, New York, 105–116, 1993. Liu, S. L. and Chow, W. K.: A review on numerical simulation of turbulent flow, Int. J. Architectural Science, 3, 77–102, 2002. Lowe, D. R.: Sediment gravity flow: depositional models with special reference to the deposits of high turbidity currents, J. Sed. Petrol., 52, 279–297, 1982. Luongo, G., Perrotta, A., and Scarpati, C. Impact of 79 AD explosive eruption on Pompeii, I. Relations amongst the depositional mechanisms of the pyroclastic products, the framework of the buildings and the associated destructive events, J. Volcanol. Geotherm. Res., 126, 201–223, 2003. Macedonio, G., and A. Neri, Fluid dynamics models of pyroclastic dispersion processes from explosive eruptions, Capricious Earth: Models and Modelling of Geologic Processes and Objects, edited by: Glebovitsky, V. A. and Dech, V. N. Theophrastus, Athens, 101–122, 2000. Moeng, C. H.: A large eddy-simulation model for the study of planetary boundary-layer turbulence, J. Atmos. Sci., 41, 2052–2062, 1984. Neri, A. and Dobran, F.: Influence of eruption parameters on the thermofluid dynamics of collapsing volcanic columns, J. Geophys. Res., 99, 833–857, 1994. Neri, A. and Macedonio, G.: Numerical simulation of collapsing volcanic columns with particles of two sizes, J. Geophys. Res., 101, 8153–8174, 1996. Neri, A., Di Muro, A., and Rosi, M.: Mass partition during collapsing and transitional columns by using numerical simulations, J. Volcanol. Geotherm. Res., 115, 1–18, 2002. Neri, A., Esposti Ongaro, T., Macedonio, G., and Gidaspow, D.: Multiparticle simulation of collapsing volcanic columns and pyroclastic flow, J. Geophys. Res., 108, 1–24, 2003. Nieuwstadt, F. T. M., Mason, P. J., Moeng, C. H., and Schumann, U.: Large eddy-simulation of the convective boundary layer: A comparison of four computer codes, in Turbulent Shear Flow 8, edited by: Durst, F., Friedrichs, R., Launder, B. E., Schmidt, F. W., Schumann, U., and Whitelaw, J. H., Springer-Verlag, New York, 343–367, 1991. Oberhuber, J. M., Herzog, M., Graf, H. F., and Schwanke K.: Volcanic plumes simulation on large scales, J. Volcanol. Geotherm. Res., 87, 29–53, 1998. Odier, P., Chen, J., Rivera, M. K., and Ecke1, R. E.: Fluid Mixing in Stratified Gravity Currents: The Prandtl Mixing Length, Phys. Rev. Lett., 102, 1–4, 2009. Patankar, S.: Numerical heat transfer and fluid flow, Hemisphere Publishing Corporation, 1980. Rivard, W. C. and Torrey, M. D.: K-FIX: A computer program for transient, two-dimensional, twofluid flow, LA-NUREG-6623, Los Alamos Natl. Lab., Los Alamos, New Mexico, 1977. Smagorinsky, J.: Some historical remarks of the use of nonlinear viscosities, in Large Eddy Simulation of Complex Engineering and Geophysical Flows, edited by: Galperin, B. and Orszag, S. A., Cambridge Univ. Press, New York, 3–36, 1993. Sparks, R. S. J.: Grain size variations in ignimbrites and applications for the transport of pyroclastic flows, Sedimentol., 23, 147–188, 1976. Srivastava, A. and Sundaresan S.: Analysis of a frictional-kinetic model for gas-particle flow, Powder Tecnology, 129, 72–85, 2003. Syamlal, M.: A review of granular stress constitutive relations, Topical Rep. DOE/MC/213532372, DE870, 649, U.S. Dep. of Energy, Washington, D. C., 23, 1987. Syamlal, M.: MFIX documentation: Numerical technique, DOE/MC/31346-5824, DE98002029, U.S. Dep. of Energy, Washington, D. C., 80, 1998. Syamlal, M., Rogers, W., and O'Brien, T. J.: MFIX documentation: Theory guide, DOE/METC-94/ 1004, DE9400, 097, U.S. Dep. of Energy, Washington, D. C., 49, 1993 Todesco, M., Neri, A., Esposti Ongaro, T., Papale, P., Macedonio, G., Santacroce, R., and Longo A.: Pyroclastic flow hazard assessment at Vesuvius (Italy) by using numerical modelling. I. Largescale dynamics, Bull. Volcanol., 64, 155–177, 2002. Valentine, G. A.: Eruption column physics, in From Magma to Tephra, edited by A. Freundt and M. Rosi, Elsevier Sci., New York, 91–138, 1998. Valentine, G. A. and Wohletz, K. H.: Numerical models of Plinian eruption columns and pyroclastic flows, J. Geophys. Res., 94, 1867–1887, 1989. Valentine, G. A., Wohletz, K. H., and Kieffer, S. W.: Sources of unsteady column dynamics in pyroclastic flow eruptions, J. Geophys. Res., 96, 887–892, 1991. Valentine, G., Zhang, D., and Robinson, B. A.: Modelling complex, nonlinear geological processes", Annu. Rev. Earth Pl. Sc., 30, 35–64, 2002. Wohletz, K. H., McGetchin, T. R., Sandford, M. T., and Jones, E. M.: Hydrodynamic aspects of caldera-forming eruptions: Numerical models, J. Geophys. Res., 89, 8269–8285, 1984. Woods, A. W.: The dynamics of explosive volcanic eruptions, Rev. Geophys., 33, 495–530, 1995. Zhang, Y.: A criterion for the fragmentation of bubbly magma based on brittle failure theory, Nature, 402, 648–650, 1999.