Wave propagation algorithms for multicomponent compressible flows with applications to volcanic jets.

摘要

Numerical algorithms are developed for compressible multicomponent flow problems in the framework of wave propagation finite volume methods based on approximate Riemann solvers. Both models for multifluid flows, which involve pure species separated by well-defined interfaces, and for two-phase flows made of gas carrying a particulate suspension are studied.; In the context of multifluid problems, I propose a method for flows governed by an arbitrary equation of state p( E , rho) based on a local linearization of the pressure law. The scheme is able to guarantee pressure equilibrium at material interfaces, avoiding the well-known numerical difficulty of the appearance of spurious pressure oscillations.; A two-phase model for particle-laden gases is then studied, which accounts for interphase drag and heat transfer, and gravity for both phases. A wave propagation algorithm is proposed to solve the governing equations, designed to guarantee an efficient treatment of source terms, and overcome the difficulties related to the non-strictly hyperbolic character of the equations of the pressureless particulate phase. In this context, the f-wave approach is employed, which enters into the framework of a general class of Riemann solvers (Relaxation Riemann Solvers) that we have introduced in a parallel study on the relation between relaxation schemes and approximate Riemann solvers.; The multi-dimensional two-phase dusty gas model is then applied to the simulation of jets and pyroclastic dispersion processes that characterize explosive volcanic events. In particular, I focus on the decompression phase of underexpanded supersonic volcanic jets on different crater morphology, describing the fluid dynamic structures that develop in the jet thrust region, such as internal shock waves. By means of numerical simulation I investigate the main factors controlling the expansion of the eruptive mixture and the generation of wave patterns above the conduit exit, with the aim of contributing to a better understanding of the complex and highly nonlinear thermo-fluid dynamic mechanisms governing these processes.