  The question of energy concentration in approximate solution sequences
$u^\epsilon$, as $\epsilon \to 0$, of the two-dimensional incompressible Euler
equations with vortex-sheet initial data is revisited. Building on a novel
identity for the structure function in terms of vorticity, the vorticity
maximal function is proposed as a quantitative tool to detect concentration
effects in approximate solution sequences. This tool is applied to numerical
experiments based on the vortex-blob method, where vortex sheet initial data
without distinguished sign are considered, as introduced in \emph{[R.~Krasny,
J. Fluid Mech. \textbf{167}:65-93 (1986)]}. Numerical evidence suggests that no
energy concentration appears in the limit of zero blob-regularization $\epsilon
\to 0$, for the considered initial data.
