Boundary layer correctors for the solution of Laplace equation in a domain with oscillating boundary

We study the asymptotic behaviour of the solution of Laplace equation in a domain with very rapidly oscillating boundary. The motivation comes from the study of a longitudinal flow in an infinite horizontal domain bounded at the bottom by a plane wall and at the top by a rugose wall. The rugose wall is a plane covered with periodic asperities which size depends on a small parameter epsilon > 0. The assumption of sharp asperities is made, that is the height of the asperities does not vanish as epsilon --> 0. We prove that, up to an exponentially decreasing error, the solution of Laplace equation can be approximated, outside a layer of width 2epsilon, by a non-oscillating explicit function.