Drag difference between steady and shocked gas flows passing through a porous body

Abstract

Experimental and numerical investigations of gas flows through porous materials have been carried out. We have investigated steady and unsteady processes occurring when the gas flow interacts with porous materials. Densities \(\rho_c\) and porosities \(\phi_g\) of the four open-cell-type polyurethane foams which were investigated are \(\rho_c \cong 26 \sim 56\) kg/m\(^3\) and \(\phi_g \cong0.98\sim 0.95\), with the foams having different structures. Experiments were conducted to determine the steady drag coefficient of the porous material at low Reynolds numbers, evaluated from the pressure drop. The Forchheimer equation was applied to determine the drag. Values of permeability coefficients (\(\alpha$, \beta\)) in the Forchheimer equation were estimated by comparing computed and experimental results. Results show that the drag coefficient is largely affected by the internal structure of the foam, and \(\alpha\) has almost no effect on the stress history, while the value of \(\beta\) dominates the stress history variation. Differences of 1000 times exist between the steady flow and unsteady shock tube flow values.