Comparison of Two Permeation Test Benches and of Two Determination Methods for Darcy's and Forchheimer's Permeabilities

Abstract

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. One of the related key issues is the estimation of permeability parameters such as Darcy's and Forchheimer's terms. The present paper aims at proposing an analytical and applied comparison of two determination methods (one based on the International Standard Organisation (ISO) norm 4022 and one derived for compressible flows, the so-called P^2 method). To apply these mathematically equivalent laws, a cross verification and validation has been carried out on two different test rigs with different porous media (metallic and composite) with a range of Darcian permeability varying from 1E−17 m^2 to 1E−11 m^ 2. The French PRISME laboratory test bench has a higher accuracy for thin samples (under 3 mm), while the German Aerospace Center (DLR) rig is more adapted to thick samples (over 3 mm). 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 of 2 for a given set of experimental data.