  For equations of order two with the Dirichlet boundary condition, as the
Laplace problem, the Stokes and the Navier-Stokes systems, perforated domains
were only studied when the distance between the holes $d_{\varepsilon}$ is
equal or much larger than the size of the holes $\varepsilon$. Such a diluted
porous medium is interesting because it contains some cases where we have a
non-negligible effect on the solution when $(\varepsilon,d_{\varepsilon})\to
(0,0)$. Smaller distance was avoided for mathematical reasons and for theses
large distances, the geometry of the holes does not affect -- or few -- the
asymptotic result. Very recently, it was shown for the 2D-Euler equations that
a porous medium is non-negligible only for inter-holes distance much smaller
than the size of the holes. For this result, the regularity of holes boundary
plays a crucial role, and the permeability criterium depends on the geometry of
the lateral boundary. In this paper, we relax slightly the regularity
condition, allowing a corner, and we note that a line of irregular obstacles
cannot slow down a perfect fluid in any regime such that $\varepsilon \ln
d_{\varepsilon} \to 0$.
