Composite materials are increasingly used in the aerospace industry, in the perspective of reducing the weight of structures and consequently fuel consumption and aviation emissions. In order to respect fire safety regulations from authorities such as ISO2685:1998(e) and FAR25.856(b):2003, numerical tools are of primary interest to avoid more classical pass or fail tests. In recent years, significant efforts were and continue to be made to understand the complex phenomena involved in composite materials’ decomposition when exposed to high heat fluxes. Models for heat and mass transfer and kinetics for pyrolysis and oxidation of composite compounds were proposed. However, comparison to experimental databases are often limited by the onset of thermomechanical damages such as delamination cracks that act as insulation layer within the composite. The present study is a first step forward filling this gap, by successfully evaluating the ability of thermal resistance to replicate the thermal consequences of delamination cracks due to laser-induced decomposition of composite coupons. Mid-term perspective is to set up a multiphysics coupling framework between thermochemical and thermomechanical degradation to allow predictive simulation of fire events.

The goal of this study is to evaluate the effects of chemical reactions between air and pyrolysis gases the modification of convective-diffusive heat flux, for a carbon/polymer composite material performing atmospheric re-entry from low Earth orbit. CFD simulations are carried out for a 2D axisymmetric sphere diameter 1 m, with an uniform blowing condition over the entire wall exposed to the flow, and considering air pyrolysis reactions. In the hypersonic community, the emission of ablation species is usually assumed to reduce heat transfer. However, this study shows that for moderate blowing rates, highly exothermic air-pyrolysis gases reactions take place sufficiently close to the wall to contribute to a significant increase in wall heat flux. At high blowing rates, convective effects dominate, and the heat transfer decreases with respect to the blowing rate. Competition between reactive and convective effects is demonstrated. The mixture composition of outgassed species is shown to have a major influence on this phenomenon. The effects of species diffusion coefficients modeling fidelity is studied by comparing two approaches: calculation of the coefficients using the Schmidt number or collision cross-section data. A deviation up to 15 % is observed between the two methods, increasing with respect to blowing rate and flow enthalpy. Simulations for a fuel tank geometry are carried out to study the effects of object's shape on the evolution of heat transfer in the presence of blowing.

CFRP composite laminates decompose by pyrolysis/oxidation when exposed to high heat fluxes. While gaseous and solid residues created within the composite material are ignored in most models, a multi-species approach is proposed to describe transient decompositions from the virgin to the final charred state of the material. The model is based on a porous medium description that includes gas creation and transport within the laminate, respectively driven by Arrhenius and Darcy’s laws. Orthotropic heat transfer and decomposition gas transport within the laminate up to the surface remain often uninvestigated while it can drastically act upon the dynamics of a fire event. An experiment is carried out to analyze multi-dimensional heat and mass transfer during the charring processes of a composite laminate exposed to a high power laser beam. Transient temperature measurements on the unexposed surface of the material are confronted to 3D unsteady numerical results to validate the model formulation.

Fire-induced decomposition of composite materials involves complex and coupled multi-physics phenomena. The modelling of such configuration presents significant challenges. In this article, we present a numerical modelling of the interaction between a turbulent propane/air premixed flame with a composite-made flat plate and its validation against detailed experimental measurements. The simulation aspects include combustion modelling, thermochemical behavior of the decomposing composite plate, as well as heat and mass transfer at the fluid/solid interface. The validation of this innovative approach is performed with an experimental database obtained on a dedicated test bench using a propane burner characterized with several optical measurement techniques including PIV (Particle Image Velocimetry), OH* imagery and BOS (Background Oriented Schlieren). Numerical results show a good correlation between simulated flame characteristics and measurements on the one side and between the composite heating dynamics and IR-thermography measurements on the other side, assessing the overall consistency of the approach proposed.

A three-dimensional strategy to compute mesh displacement following surface recession due to ablation is proposed and implemented in the finite volume material response code MoDeTheC. Due to the application to the thermal degradation of space debris during atmospheric reentry, the strategy developed is based onto a very general formulation that can deal with any mesh topology and object shape without preliminary identification of ablated surfaces. First, a new moving mesh method modifies the grid to take into account changes due to ablation. Subsequently, a shape preservation mesh balancing method redistributes the mesh vertices to maintain the grid quality. Finally, a smoothing algorithm is applied to prevent high frequency mesh oscillations. The new 3D mesh displacement strategy is verified on many 2D and 3D test cases to prove the capabilities of the method.

The spacecraft oriented code ARES developed at ON-ERA since 2005 to compute Earth and Mars atmospheric reentries is introduced. Then, a new 3D mesh displacement strategy to computed 3D space debris ablation is presented. This strategy is implemented in the material response solver MoDeTheC, which is one of the 4 independant solvers coupled within ARES code. Verification test cases show the capacity of the strategy to deal with important recession and shape changes. This strategy is then used in ARES software to rebuild a wind tunnel ablation test. Finally, the atmospheric reentry of a tank made of an orthotropic composite material is computed, taking into account degradation reaction and shape changes. Two coupling strategy in ARES software are used and compared.

Soot formation has become an important issue in the design of gas turbine combustors due to its environmental impact and its contribution to radiative heat transfer in the combustion chamber. However, efficient and accurate prediction of soot particles formation, growth, oxidation and interaction in gas turbine combustors is still an open field in computational fluid dynamics. The present approach proposes to combine a reduced gas-phase chemistry, a sectional model for polycyclic aromatic hydrocarbons, and a Lagrangian description of soot particles dynamics. The Lagrangian description has been chosen for its ability to simulate the evolution of the particle size distribution. A numerical procedure is proposed to minimise its CPU cost. This approach was successfully applied to the simulation of steady laminar premixed ethylene-air flames at three fuel equivalence ratios, which constitutes a prerequisite towards its use in an aeronautical combustion chamber.