Vorticity disturbances are introduced at a grid and convect with the uniform mean flow alongside a flat plate. The influence of the plate on this rotational, unsteady flow is found by solving Laplace’s equation in a quarter plane subject to Dirichlet boundary conditions. In the corner region downstream of the grid and near the plate, the streamline patterns do not convect with the mean flow and Taylor’s hypothesis is not valid as indicated by the velocity correlations. The influence of the plate is limited to a region from the plate to about one vortex diameter away from the plate. Near the plate and about one diameter downstream of the grid, a new streamline pattern evolves which convects along without further change. The alteration to the free-stream disturbances produced by the plate also represents the flow introduced by a wavy wall.