Airflow through polyurethane foams with near-circular cell-face holes

A range of open-cell slow-recovery polyurethane (PU) foams were found to have roughly circular cell-face holes, which are small compared with the face area. The pressure gradient through the foam was measured for airflow velocities in the range 0.5-5 ms(-1), and the permeabilities K and inertial flow coefficients B calculated. Computational Fluid Dynamics (CFD) was used for laminar airflow through both an axisymmetric model and a regular Kelvin foam model. The predicted foam permeabilities from the latter were close to the experimental values. Finite Element Analysis (FEA) was used to predict cell-face shape changes under a pressure gradient. The distorted face shapes were then used in the CFD model to explain why the B values were negative for some foams.