  We study the asymptotic behavior of the motion of an ideal incompressible
fluid in a perforated domain. The porous medium is composed of inclusions of
size $\varepsilon$ separated by distances $d_\varepsilon$ and the fluid fills
the exterior.
  If the inclusions are distributed on the unit square, the asymptotic behavior
depends on the limit of $\frac{d_{\varepsilon}}\varepsilon$ when $\varepsilon$
goes to zero. If $\frac{d_{\varepsilon}}\varepsilon\to \infty$, then the limit
motion is not perturbed by the porous medium, namely we recover the Euler
solution in the whole space. On the contrary, if
$\frac{d_{\varepsilon}}\varepsilon\to 0$, then the fluid cannot penetrate the
porous region, namely the limit velocity verifies the Euler equations in the
exterior of an impermeable square.
  If the inclusions are distributed on the unit segment then the behavior
depends on the geometry of the inclusion: it is determined by the limit of
$\frac{d_{\varepsilon}}{\varepsilon^{2+\frac1\gamma}}$ where $\gamma\in
(0,\infty]$ is related to the geometry of the lateral boundaries of the
obstacles. If $\frac{d_{\varepsilon}}{\varepsilon^{2+\frac1\gamma}} \to
\infty$, then the presence of holes is not felt at the limit, whereas an
impermeable wall appears if this limit is zero. Therefore, for a distribution
in one direction, the critical distance depends on the shape of the inclusions.
In particular it is equal to $\varepsilon^3$ for balls.
