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We investigate the scale-locality of subgrid-scale (SGS) energy flux andinter-band energy transfers defined by the sharp spectral filter. We show byrigorous bounds, physical arguments and numerical simulations that the spectralSGS flux is dominated by local triadic interactions in an extended turbulentinertial-range. Inter-band energy transfers are also shown to be dominated bylocal triads if the spectral bands have constant width on a logarithmic scale.We disprove in particular an alternative picture of ``local transfer bynonlocal triads,'' with the advecting wavenumber mode at the energy peak.Although such triads have the largest transfer rates of all {\it individual}wavenumber triads, we show rigorously that, due to their restricted number,they make an asymptotically negligible contribution to energy flux andlog-banded energy transfers at high wavenumbers in the inertial-range. We showthat it is only the aggregate effect of a geometrically increasing number oflocal wavenumber triads which can sustain an energy cascade to small scales.Furthermore, non-local triads are argued to contribute even less to thespace-average energy flux than is implied by our rigorous bounds, because ofadditional cancellations from scale-decorrelation effects. We can thus recoverthe -4/3 scaling of nonlocal contributions to spectral energy flux predicted byKraichnan's ALHDIA and TFM closures. We support our results with numerical datafrom a $512^3$ pseudospectral simulation of isotropic turbulence withphase-shift dealiasing. We conclude that the sharp spectral filter has a firmtheoretical basis for use in large-eddy simulation (LES) modeling of turbulentflows.

Localness of energy cascade in hydrodynamic turbulence, II. Sharp spectral filter