  A generalization of the $3D$ Euler-Voigt-$\alpha$ model is obtained by
introducing derivatives of arbitrary order $\beta$ (instead of $2$) in the
Helmholtz operator. The $\beta \to \infty$ limit is shown to correspond to
Galerkin truncation of the Euler equation. Direct numerical simulations (DNS)
of the model are performed with resolutions up to $2048^3$ and Taylor-Green
initial data. DNS performed at large $\beta$ demonstrate that this simple
classical hydrodynamical model presents a self-truncation behavior, similar to
that previously observed for the Gross-Pitaeveskii equation in Krstulovic and
Brachet [Phys. Rev. Lett. 106, 115303 (2011)]. The self-truncation regime of
the generalized model is shown to reproduce the behavior of the truncated Euler
equation demonstrated in Cichowlas et al. [Phys. Rev. Lett. 95, 264502 (2005)].
The long-time growth of the self-truncation wavenumber $k_{\rm st}$ appears to
be self-similar.
  Two related $\alpha$-Voigt versions of the EDQNM model and the Leith model
are introduced. These simplified theoretical models are shown to reasonably
reproduce intermediate time DNS results. The values of the self-similar
exponents of these models are found analytically.
