in a perforated domain, the asymptotic behavior of the fluid motion depends on the rate (inter-hole distance)/(size of the holes). we will present the standard framework and explain how to find the critical rate where "strange terms" appear for the laplace and navier-stokes equations. next, we will study euler equations where the critical rate is totally different than for parabolic equations. these works are in collaboration with v.bonnaillie-noel, m.hillairet, n.masmoudi, c.wang and d.wu.