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The coking phenomenon within low- density ablative material exposed to aerodynamic heating is studied. The char density of the tested material is measured by slicing the material thinly, and by weighing each of the sliced test pieces. Measured density profiles of the tested materials are compared with the calculated results obtained by a thermal response code. The surface and internal state of both pre- and post- materials are observed by using Scanning Electron Microscope (SEM) and X-ray Computed Tomography (CT). The results show that the measured density profiles is inversely increased to the heated surface. The density increase is likely due to the deposition of a solid carbon in the char region during aerodynamic heating., 資料番号: AA0063742010, レポート番号: JAXA-SP-07-016

International audience; abstractThe use of composite materials for aeronautical applications has been growing since several years be- cause 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 nu- merical 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 certi- fication rules compare to the actual external thermal protection used to ensure the certification re- quirements. Indeed, final temperature reductions up to 45% are found at reference point on the structure with the highest value of air jet velocity.

A trajectory-based heating analysis of the Galileo probe entry flowfield is attempted to reproduce the heatshield recession data obtained during the entry flight. In the present calculation, the mass conservation equations for the freestream gas (hydrogen-helium gas mixture) and the ablation product gas are solved with an assumption of thermochemical equilibrium. The ablation process is assumed to be quasi-steady and is coupled with the flowfield calculation. The radiative energy transfer calculation is tightly coupled with the flowfield calculation, where the absorption coefficients of the gas mixture are given by the multiband radiation model having 4,781 wavelength points for wavelength range from 750 to 15,000 A. The injection-induced turbulence model proposed by Park is employed to account for the enhanced turbulence effect due to the ablation product gas. It is shown that the final recession profile of the flight data at the frustum region can be closely reproduced if the injection-induced turbulence model is employed, although that at the stagnation region is overestimated. The cause of the enhanced radiative heating that occurs at the frustum region is given in connection with the enhanced turbulence effect in the shock layer., 資料番号: AA0048469010, レポート番号: JAXA-SP-04-012