  The explicit filtering method for large eddy simulation (LES,) which
comprises integration of the governing equations without any added terms for
sub-grid-scale modeling, and the application of a low-pass filter to
transported fields, is discussed. The shapes of filter response functions of
numerical schemes for spatial derivatives and the explicit filter, that have
been used for several LES, are examined. Generally, these are flat (no
filtering) over a range of low wavenumbers, and then fall off over a small
range of the highest represented wavenumbers. It is argued that this high
wavenumber part can be viewed as a spectral buffer analogous to physical buffer
(or sponge) zones used near outflow boundaries. The monotonic convergence of
this approach to a direct numerical simulation, and the shifting of the
spectral buffer to larger wavenumbers as the represented spectral range is
increased, without altering the low wavenumber part of solutions, is
demonstrated with LES of two sample flows. Connections to other widely used
methods---the Smagorinsky model, MILES and another ILES---are also explained.
