The potential flow signature of a turbulent spot

Measurements were made at a nominal free stream velocity of 11 m/s in a closed circuit wind tunnel. Turbulent spots were generated by means of a capacitive discharge between stainless steel sewing needles protruding a distance of 1 mm into the boundary layer. It was found that the unsteady potential flow signatures generated by a turbulent spot can be fairly well represented by a two-dimensional similarity calculation for the flow over a moving bump on the wall, whose shape is given by the instantaneous displacement thickness distribution along the wall on the spot centerline. If the fully turbulent boundary layer can be represented as a flow containing a collection of turbulent spots, then one might expect to see similar signatures in the potential flow outside the fully turbulent layer.