Multiscale CFD of the Flow, Heat and Mass Transfer Through a Porous Material With Application to Protective Garments

A multi-scale study of the performance of protective clothing has been performed by coupling various types of numerical simulation of flow, heat and mass transfer. At first, a detailed study of the turbulent flow at Re = 3900 around a circular cylinder, sheathed at some small distance by a porous layer, has been performed by means of Direct Numerical Simulations with a commercial unstructured finite volume based Computational Fluid Dynamics solver. This geometry is widely used in experiments to study the performance of fabric materials. From this DNS study, it was found that the flow underneath the clothing is laminar and periodic, with a velocity magnitude much smaller than the free stream velocity. Micro-scale Direct Numerical Simulations of the flow through the textile at the scale of individual fibres revealed a simple relation between textile porosity and permeability. A good agreement was found between flow and heat transfer predictions of Direct Numerical Simulations and from Reynolds Averaged simulations. From the latter, an engineering correlation for heat and mass transfer was deduced.