Alice Marinescu

Permeability measurement of easily deformable porous materials saturated with liquids represents a costly and time-consuming process, usually performed with complex experimental devices. This study proposes an alternative approach for evaluating the in-plane permeability of 3D warp-knitted spacer fabrics under compression. A 3D model was reconstructed from scanned images, and its behavior was analyzed using the finite-element method. The resulting deformed shapes of the representative cell were used in computational fluid dynamics simulation to assess the permeability across a wide compression range, approaching the densification phase. The permeability was determined from Darcy’s law at reduced flow speeds, whereas higher flow speeds were analyzed using the quadratic extension (Forchheimer) of the linear regime. Finally, simulation results at various compression ratios showed good agreement with experimental measurements, thus validating the numerical approach.

Aerostatic bearings were proven to be an optimal choice in situations where low friction, cleanliness, and high motion accuracy are required. Their functionality relies heavily on flow restrictors, which are responsible for regulating and controlling the supply flow, and consequently, the thickness and stiffness of the fluid film. A diverse range of restrictors with varying characteristics is used, among which are the porous restrictors. The current work introduces a novel solution involving a porous, highly compressible restrictor, whose element of novelty compared to its predecessors consists of its variable thickness and corresponding permeability, regulated by the load on the bearing. The gas is supplied through an annular, elastic, deformable, porous disc, which is compressed by a metal plate, subjected to compression by the recess pressure on one side and by the supply pressure on the other side. One or more springs are used in parallel with the porous disc to obtain the optimum elastic response. The objective of this study is to evaluate the performance characteristics and compare them to a conventional restrictor. A parametric analysis is performed to define the size and properties of the porous restrictor.