  The flow inside remnants of binary neutron star (NS) mergers is expected to
be turbulent, because of magnetohydrodynamics instability activated at scales
too small to be resolved in simulations. To study the large-scale impact of
these instabilities, we develop a new formalism, based on the large-eddy
simulation technique, for the modeling of subgrid-scale turbulent transport in
general relativity. We apply it, for the first time, to the simulation of the
late-inspiral and merger of two NSs. We find that turbulence can significantly
affect the structure and survival time of the merger remnant, as well as its
gravitational-wave (GW) and neutrino emissions. The former will be relevant for
GW observation of merging neutron stars. The latter will affect the composition
of the outflow driven by the merger and might influence its nucleosynthetic
yields. The accretion rate after black-hole formation is also affected.
Nevertheless, we find that, for the most likely values of the turbulence mixing
efficiency, these effects are relatively small and the GW signal will be
affected only weakly by the turbulence. Thus, our simulations provide a first
validation of all existing post-merger GW models.
