Numerical investigation of the heat transfer in an aeronautical composite material under fire stress

The use of composite materials for aeronautical applications has been growing since several years because of the opportunity to produce lightweight structures reducing the fuel bills and emissions. The need for fireproof certification imposes costly and time consuming experiments that might be replaced or complemented in the years to come by numerical calculations. The present work creates a CFD numerical model of a fireproof test. As an example, a composite part located in an aircraft APU (auxiliary power unit) which provides electric power to the aircraft is investigated. A numerical calibration of the flame is conducted according to the fireproof standards. After that, a comparison between three different turbulence models shows that the k-ε realisable turbulence model is the more suitable for fireproof numerical tests with discrepancies lower than 16% between computed values and measured ones. The influence of an internal air jet is observed for velocities from 1 to 10 m/s. The results demonstrate a good evaluation on how this could reduce the wall temperatures and ensure the requirements of the certification rules compare to the actual external thermal protection used to ensure the certification requirements. Indeed, final temperature reductions up to 45% are found at reference point on the structure with the highest value of air jet velocity.