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Section: New Results

Numerical simulation of the liquid ablation

Participants : Gérard Gallice, Luc Mieussens [Corresponding member] , Simon Peluchon.

During the atmospheric re-entry phase, a space vehicle undergoes a heating due to the friction of the atmospheric gases. Conversion of kinetic energy to thermal energy leads to a sudden increase of the temperature of the solid boundary. This leads to a physical-chemical degradation of the thermal protective system, and to a boundary recession. For some materials, this recession occurs with a melting of the materials into a fluid phase. The numerical simulation of this phenomenon requires to take into account a two-phase flow with a compressible gaz (the air flow) and a weakly compressible liquid (the melted material). Numerically, this problem is strongly stiff.

We have proposed a splitting strategy to simulate compressible two-phase flows using the five equation model. The main idea of the splitting is to separate the acoustic and transport phenomena. The acoustic step is solved in Lagrangian coordinates by using a scheme based on an approximate Riemann solver. On the one hand, since the acoustic time step driven by the fast sound velocity is very restrictive, an implicit treatment of the Lagrangian step is performed. On the other hand, we use an explicit scheme for the transport step driven by the slow material waves. The global scheme resulting from this splitting operator strategy is conservative, positive, and preserves contact discontinuities. Numerical simulations of compressible diphasic flows are presented on 2d-structured grids. The implicit-explicit strategy allows large time steps, which do not depend on the fast acoustic waves.