On the stability of wake flows past porous bluff bodies

Inspired by nature and motivated by engineering applications, the study of the flow past and through porous media has received a growing interest in our community over the years. In this work, we present results from a numerical study aimed to investigate the effect of the porosity and permeability on the transition scenario of the wakes of porous bluff bodies at low-moderate Reynolds numbers. This work is developed in the framework of direct numerical simulation and linear stability analysis. First, the two-dimensional flow past porous rectangular cylinders is investigated, considering thickness-to-height ratios ranging from 0.01 (flat plate) to 1.0 (square cylinder). Then, the cases of the flow past a porous sphere and a disk are studied. The results show that the permeability of the bodies has a strong effect in modifying the characteristics of the flow instabilities, while the porosity weakly affects the flow patterns. In particular, since the fluid can flow through the porous obstacles, the recirculation regions detach from the body first and then disappear in the near wakes when the permeability is increased. Lastly, for all the configurations here presented, critical values of the permeability are furthermore identified above which any flow instabilities are prevented.