A depth-averaged, two-phase flow code for hazard mapping that satisfies both hydraulic and granular flow extremes
Abstract
Ground-hugging particle-laden flows constitute some of the most dangerous natural phenomena on Earth. Such currents, in the form of snow avalanches, pyroclastic flows, debris flows, lahars, and landslides, are among the most destructive processes in nature. Humans tend to settle in areas near rich soils, volcanoes, or watercourses, all of which could be strongly affected by these dangerous flows. In order to improve risk preparedness and site management in potentially affected zones, an appropriate knowledge of these natural hazardous phenomena is required. Their evolution in time, flow dynamics and run out distance are key aspects that help in the planning for hazardous events, development of hazardous regions and design of management policy to prepare in advance of potential natural disasters. This paper describes a depth-averaged model for two-phase flow that is currently under development at the University at Buffalo. It is being implemented within the TITAN2D framework that presently simulates dry geophysical mass flows over natural-scale terrains. The initial TITAN2D code was created to simulate granular flow. But because the presence of an interstitial fluid strongly modifies the dynamics of the flow, a new, more general, two-phase model is needed to account for the broad range in volume fraction of solids that occurs in nature. The mathematical model depth-integrates the Navier-Stokes equations for each phase, solid and fluid. The solid phase is modeled assuming a Coulomb constitutive behavior at the theoretical limit of pure solids. In contrast, the fluid phase conforms to a typical hydraulic approach at the limit of pure fluid and uses the Darcy-Weisbach approach to account for bed friction. The linkage for compositions between the pure end-member single phases is accommodated by the inclusion of a phenomenological-based drag coefficient. The model is capable of simulating the whole range of particle volumetric fractions, from pure fluid flows to pure solid avalanches. There is no constraint regarding the kind of interstitial fluid, provided that its density and viscosity can be assumed as constants.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.V12C..04C
- Keywords:
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- 8488 VOLCANOLOGY / Volcanic hazards and risks