Influence Of Porous Materials Research Articles

Influence of porous material on the flow behind a backward-facing step: experimental study

We investigate effect of porous insert located upstream of the separation edge of a backward-facing step (BFS) in early transitional regime as a function of Reynolds number. This is an example of hydrodynamic system that is a combination of separated shear flow with large amplification potential and porous materials known for efficient flow destabilisation. Spectral analysis reveals that dynamics of BFS is dominated by spectral modes that remain globally coherent along the streamwise direction. We detect two branches of characteristic frequencies in the flow and with Hilbert transform we characterise their spatial support. For low Reynolds numbers, the dynamics of the flow is dominated by lower frequency, whereas for sufficiently large Reynolds numbers cross-over to higher frequencies is observed. Increasing permeability of the porous insert results in decrease in Reynolds number value, at which frequency cross-over occurs. By comparing normalised frequencies on each branch with local stability analysis, we attribute Kelvin–Helmholtz and Tollmien–Schlichting instabilities to upper and lower frequency branches, respectively. Finally, our results show that porous inserts enhance Kelvin–Helmholtz instability and promote transition to oscillator-type dynamics. Specifically, the amplitude of vortical (BFS) structures associated with higher-frequency branch follows Landau model prediction for all investigated porous inserts.

Study on the influence of porous material on underwater vehicle's hydrodynamic characteristics

As humans accelerate the pace of marine development, autonomous underwater vehicles (AUVs) are increasingly attracting worldwide attention. Due to the limitations of carrying energy and battery technology, AUV's endurance is nonideal. Therefore, designers usually make AUVs more streamlined to reduce drag. Here we show that when a layer of porous material is attached to an AUV's surface, the AUV's drag changes significantly. In this paper, simulations of the basic body of a REMUS100 and SUBOFF submarine model were carried out under multiple conditions. It is found that the drag increases as the porous viscosity coefficient or the thickness of the porous material increases. When REMUS100 and SUBOFF models are attached to the porous material with suitable porous viscosity coefficient, their drag becomes smaller. Boundary layer theory is also used to explain and analyze the phenomenon of the proportional increase of viscous pressure drag when using porous material, which is verified by vertical plate numerical simulations. Finally, we tested the mechanical properties of porous nickel and aluminum alloy 6061, and found that the porous material does have an effect of drag reduction, and can reduce the fluctuation range of the drag during the movement.

Vortex sound under the influence of a piecewise porous material on an infinite rigid plane

The vortex dynamics and the sound generation by an inviscid vortex in the presence of a finite length porous material on an otherwise rigid plane are studied numerically in the present study in an attempt to understand the sound generation near the surface of a wall lining in a lined duct. The combined effects of the effective fluid density and flow resistance inside the porous material, and the length and thickness of the porous material on the sound generation process are examined in detail. Results obtained demonstrate the sound pressure is longitudinal dipole and show how seriously the above-mentioned parameters are affecting the vortex sound pressure under the influence of the porous material.

Influence of Porous Materials on Water Supply Characteristic of Sub-irrigation Method

Influence of Porous Materials on Water Supply Characteristic of Sub-irrigation Method