ASHEE

By Matteo Cerminara1, Tomaso Esposti Ongaro1

1. Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Pisa

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Abstract

A 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 particles, we adopt an asymptotic expansion strategy to derive a compressible version of the first-order non-equilibrium model, valid for low concentration regimes and small particles Stokes number St<0.2. When St<0.001, the model reduces to the dusty-gas one. The new model is significantly faster than the Eulerian model while retaining the capability to describe gas-particle non-equilibrium. Direct numerical simulation accurately reproduce the dynamics of isotropic turbulence in subsonic regime. For gas-particle mixtures, it describes the main features of density fluctuations and the preferential concentration of particles by turbulence, verifying the model reliability and suitability for the simulation of high-Reynolds number and high-temperature regimes. On the other hand, Large-Eddy Numerical Simulations of forced plumes are able to reproduce their observed averaged and instantaneous properties. The self-similar radial profile and the development of large-scale structures are reproduced, including the rate of entrainment of atmospheric air. Application to the Large-Eddy Simulation of the injection of the eruptive mixture in a stratified atmosphere describes some of important features of turbulent volcanic plumes, including air entrainment, buoyancy reversal, and maximum plume height. Coarse particles partially decouple from the gas within eddies, modifying the turbulent structure, and preferentially concentrate at the eddy periphery, eventually being lost from the plume margins due to the gravity. By these mechanisms, gas-particle non-equilibrium is able to influence the large-scale behavior of volcanic plumes.

Tags

  1. ash
  2. ash aggregation
  3. ash clouds
  4. ash deposits
  5. ash detection
  6. ash dispersal forecast
  7. ashee
  8. ashfall deposits
  9. ash fall mapping and grains size distribution
  10. ash fall simulation
  11. ash flow
  12. ash observation
  13. ash transport
  14. deposit
  15. DNS
  16. Large-Eddy Simulations
  17. LES
  18. numerical analisys
  19. numerical model
  20. numerical modeling
  21. numerical modelling
  22. numerical simulation
  23. numerical simulations
  24. OpenFOAM
  25. particle concentration
  26. particle fallout
  27. particles
  28. plume
  29. plume and tephra dispersion
  30. plume height
  31. Plume model
  32. plumes
  33. pyroclastic density current
  34. pyroclastic density currents
  35. Pyroclastic Density Currrents
  36. pyroclastic deposits
  37. pyroclastic flows
  38. Pyroclastic Gravity Currents
  39. Pyroclastic volcanism
  40. pyroclast transport
  41. tephra
  42. Tephra correlation
  43. tephra deposits
  44. Tephra dispersal and atmospheric transport of volcanic ash
  45. tephra dispersion
  46. Tephra dispersion and modeling
  47. Tephra Dispersion Models
  48. tephra fallout
  49. Tephra transport
  50. turbulence
  51. volcanic ash
  52. volcanic ash monitoring and forecasting
  53. volcanic behaviour
  54. volcanic cloud
  55. volcanic cloud transport
  56. volcanic degassing
  57. volcanic deposits
  58. Volcanic eruption