The following literature  may be useful for your research

Absract: In this work, flow permeation through a porous circular cylinder located symmetrically between two impermeable parallel plates is investigated numerically under different flow and geometrical conditions. A flow interception efficiency is defined and calculated based on the flow permeation rate for a wide range of system parameters. The dependencies on all physical variables can be

captured in three dimensionless numbers: the Reynolds number, the Darcy number (ratio of permeability to the square of cylinder diameter), and the plate separation relative tothe cylinder size. The flow interception efficiency is very low in the limit of unboundedcylinders but significantly increases by restricting the flow domain. The fluid permeation rate through the porous cylinder varies nonlinearly with the relative plate/cylinder spacing ratio, especially when the gap between the cylinder and the confining plates is small compared to the cylinder size. In general, the effects of the Reynolds number, the Darcy number, and confinement on the flow interception efficiency are coupled; however, for most practical cases it is possible to factorize theseeffects. For practical ranges of the Darcy number (Da < 10 ^−4, which means that thepore size is at least one order of magnitude smaller than the porous cylinder diameter),the interception efficiency varies linearly with Da, is independent of the Reynoldsnumber at low Reynolds numbers (Re < 10), and varies linearly with Reynoldsnumber at higher flow rates.

Ref:Interception efficiency in two-dimensional flow past confined porous cylinders 

Setareh Shahsavari*, Brian L. Wardle†, Gareth H. McKinley*

web.mit.edu/nnf/publications/GHM217.pdf

In another reference,

Abstract: Convective heat transfer from cylinders embedded in porous media is important for many engineering applications. In the present study, flow-field and heat transfer around a cylinder embedded in a layer of homogenous porous media is investigated numerically. The range of Reynolds and Darcy numbers are chosen to be 1–40 and (1 × 10^ −8)–(1 × 10^ −1), respectively. Volume averaged equations are used for modeling transport phenomena within the porous layer and conservation laws of mass, momentum, an energy are applied in the clear region. A comprehensive parametric study is carried out and effects of several parameters, such as porous layer thickness and permeability as well as the Darcy and Reynolds numbers on flow-field and heat transfer characteristics are studied. Finally an optimization process is conducted in order to determine the optimal thickness and porosity of the porous layer resulting in the lowest heat transfer from the cylinder. The numerical results indicate that, in the presence of a porous layer around the cylinder, the wake length increases with decreasing the Darcy number while the critical radius of insulation increases. 

Ref: Fluid flow and forced convection heat transfer around a solid cylinder wrapped with a porous ring

Saman Rashidia, Ali Tamayolb, c, Mohammad Sadegh Valipoura, Nima Shokri

International Journal of Heat and Mass Transfer

Volume 63, August 2013, Pages 91–100

www.linknovate.com/search/?...fluid%20flow%20around%20a%20cylin...

thanks a lot

One has to use caution on interpreting CFD results since CFD doesn't represents the reality but rather a filtered reality. Real flows are never steady state with stable stream lines, the most common occurence is the von Karman vortex alley. This phenomenon makes wrong most of the uncalibrated CFD analysis, not so apparent in drag estimation but very apparent in heat transfer estimaton. This being said, the porous layer may dampen the von Karman vortex sheding thus reducing the drag when compared with plain cylinder. Varying the permeability/impedance/Darcy number will change the degree of dampening with a maximum at an intermediate value; such behaviour is expected since a highly permeable porous layer has a reduced dispation although it allows a high flow rate to penetrate the layer, while at low permeability porous layer may have high disipation rate but this will apply to a low flow rate penetrating the layer. The square has corners that are strong vortex generators/stabilizers, which may change the relationship between the CFD filtered estimates and actual vortex sheding effects.

I invite you to have a look on this paper and similar one published in JFM

 Boundary conditions for creeping flow along periodic or random rough surfaces : experimental and theoretical results

Nicolas Lecoq

Journal of Physics Conference Series 12/2012; 392(1):2010

thanks Nicolas