Micro model for calculating flow resistivity for anisotropic open cell materials with high aspect ratio of struts
2016 (English)Report (Other academic)
Micro-structure models for calculating flow resistivity for open cell materials with high aspect ratio of struts are presented. Two micro-geometries are analyzed and compared: the hexahedral model, with the solid frame in shape of a cube for the isotropic case, and the tetrakaidecahedron (Kelvin cell). For flow resistivity calculations the solid frame is assumed to be rigid. The models are elongated in one direction to study the influence of micro-structural anisotropy on the macro level flow resistivity. In order to evaluate how the redistribution of material affects the flow resistivity, the porosity of the material is kept constant. Since the porosity is defined as unity minus the ratio of strut volume of the cell to the total volume of the cell, there are different ways of linking the micro level properties to the macro level. The first approach presented here is to let strut thickness be uniform and adjust the volume of the cell to a constant ratio compared to the isotropic case. The second approach is to let the strut volume be constant, i.e. if a strut is elongated, it is also thinner. In this case the cell volume must equal the isotropic volume. For uniform strut thickness the flow resistivity increases substantially with increasing height to width ratio for the hexahedral model, and decreases for the Kelvin cell. For constant strut volume the flow resistivity perpendicular to the flow direction increases, and the other direction (where the strut thickness increases) will be reduced. The average flow resistivity will in this case be almost constant. The method of scaling the micro-cell properties has a high influence on the resulting average flow resistivity, as does the cell volume in relation to the isotropic volume. For open porous materials which are approximately isotropic, the choice of micro geometry is not so critical and can be determined by other considerations, such as elasticity.
Place, publisher, year, edition, pages
2016. , 19 p.
acoustics, foam, micro-structure, flow resistivity, strut, anisotropy
Fluid Mechanics and Acoustics
Research subject Vehicle and Maritime Engineering
IdentifiersURN: urn:nbn:se:kth:diva-187321OAI: oai:DiVA.org:kth-187321DiVA: diva2:929826
QC 201605242016-05-202016-05-202016-05-24Bibliographically approved