Experimental study on the lift generation inside a random synthetic porous layer under rapid compaction

Lift generation in a soft porous medium under rapid compaction is a new concept for porous media flow. This concept is of extraordinarily broad interest since it applies to such diverse problems as the motion of a red cell in a tightly fitting capillary [8], the lifting forces generated during skiing or snowboarding [22], and the design of a futuristic train track [18] and [19], in addition to classical lubrication theory applications [13] and [14]. In this paper, we developed a systematic, experimental approach to examine the pore pressure generation inside a deformable porous medium. To accomplish this task, a novel porous-walled cylinder–piston apparatus was developed. This apparatus was fully instrumented with pressure transducers, an accelerometer and a displacement sensor. Two synthetic fibers with different microstructures and mechanical properties were tested under various, precisely-controlled loading conditions. Enhanced lift was observed for both of them. The results indicated that lift generation inside a compressible porous medium strongly depends on the material properties and loading conditions. Softer material with lower Darcy permeability was able to generate higher pore pressure, although lowering the permeability of a porous medium was usually accompanied by the increase in the solid phase contribution to the total lift and thus led to the decrease in the pore fluid pressure. It was also observed that higher pore pressure was generated if the porous layer thickness was increased. The study presented herein has provided a rigorous approach for experimentally examining the lift generation in a deformable porous medium. It is of significant importance for the designs of rotational squeeze dampers and shock absorbers, as well as for the application of highly compressible porous media for enhanced lubrication.