HR: 0800h
AN: V31D-0643    [Abstracts]
TI: Validation of a numerical model of eruption clouds using experimental and field data
AU: * Suzuki, Y J
EM: yujiros@jamstec.go.jp
AF: Japan Agency for Marine-Earth Science and Technology, 3173-25, Showa-machi, Kanazawa-ku, Yokohama, 236-0001 Japan
AU: Koyaguchi, T
EM: tak@eri.u-tokyo.ac.jp
AF: Earthquack Research Institute, University of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AB: Explosive volcanic eruptions generate eruption columns, pyroclastic flows, and umbrella clouds (i.e., eruption clouds). The dimensions and dynamics of eruption clouds are primarily governed by entrainment of ambient air into eruption clouds by turbulent mixing. We have developed a numerical pseudo-gas model of eruption clouds which reproduces quantitative features of turbulent mixing. For validation of the model, we compare our numerical results with experimental data of turbulent jet into a uniform environment and field data of eruption clouds. A number of experimental studies on a turbulent jet or plume which is ejected into a uniform environment have revealed that such a jet or plume is characterized by the self-similarity that the radial length scale is proportional to the distance from the nozzle, and the time-averaged profile of velocity at a given height has a Gaussian distribution. It is also suggested that the efficiency of turbulent mixing no longer depends on the Reynolds number when the turbulence is fully developed. Our numerical model has successfully reproduced these features of turbulent mixing when third-order accuracy scheme with a fine grid size (smaller than L/5 in our model, where L is the nozzle radius) is applied in three-dimensional coordinates. Our numerical model is applicable to the dynamics of eruption clouds by changing the equation of state. In turbulent jets and plumes of eruption clouds, the self-similarity is not always valid in a strict sense because of the non-linearity of the equation of state, the atmospheric stratification and the large length scale of source. On the other hand, it is considered that the mixing efficiency of eruption clouds must be independent of the Reynolds number, because the turbulence is fully developed. We have systematically performed sensitivity tests with different grid sizes to find the condition where the mixing efficiency no longer depends on the grid size (i.e., independent of the numerical Reynolds number). The validation of the present model has also been done using field data such as satellite images of spreading umbrella cloud.
DE: 0545 Modeling (4255)
DE: 4490 Turbulence (3379, 4568, 7863)
DE: 8428 Explosive volcanism
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005