Comparison of Two Permeation Test Benches and of Two Determination Methods for Darcy's and Forchheimer's Permeabilities
Résumé
The thermal load protection of hypersonic and space vehicle structures can be achieved by either passive or active methods, such as ablative materials or active cooling. For the latter, porous Ceramic Matrix Composite media offer a possibility to exploit thermal protection by means of transpiration cooling due to their higher permeability. One of the related key issues is the determination of permeability parameters such as the Darcy's and Forchheimer's terms. The present paper aims at proposing an analytical and applied comparison of two of them (one based on the international norm ISO4022 and one derived for compressible flows, the P² method). To apply these mathematically equivalent laws, a cross verification and validation has been realized on two different test rigs with different porous media (metallic and composite) with a range of Darcian permeability varying from 10-17 m² to 10-11 m². The PRISME test bench has a lower accuracy for thick samples (over 3 mm) due to lateral permeation while the DLR rig is free from such a phenomenon thanks to an innovative sealing (which is however not adapted to samples thinner than 3 mm). The two test rigs are found to be complementary. The results are judged to be satisfactory (discrepancy around 14 % for reference samples). The methods used to post-process the data can generate discrepancies up to a factor 2. The method based explicitly on compressibility is chosen more specifically for its easiest application to Computational Fluid Dynamics. The ISO method accuracy is lower for small flow rate range.
Domaines
Matériaux
Origine : Fichiers produits par l'(les) auteur(s)
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