  We study the evolution of an accelerating hyperrelativistic shock under the
presence of upstream inhomogeneities wrinkling the discontinuity surface. The
investigation is conducted by means of numerical simulations using the PLUTO
code for astrophysical fluid dynamics. The reliability and robustness of the
code are demonstrated against well known results coming from the linear
perturbation theory. We then follow the nonlinear evolution of two classes of
perturbing upstream atmospheres and conclude that no lasting wrinkle can be
preserved indefinitely by the flow. Finally we derive analytically a
description of the geometrical effects of a turbulent upstream ambient on the
discontinuity surface.
