  The plasmoid instability may lead to fast magnetic reconnection through long
current sheets(CS). It is well known that large-Reynolds-number plasmas easily
become turbulent. We address the question whether turbulence enhances the
energy conversion rate of plasmoid-unstable current sheets. We carry out
appropriate numerical MHD simulations, but resolving simultaneously the
relevant large-scale (mean-) fields and the corresponding small-scale,
turbulent, quantities by means of direct numerical simulations (DNS) is not
possible. Hence we investigate the influence of small scale turbulence on large
scale MHD processes by utilizing a subgrid-scale (SGS) turbulence model. We
verify the applicability of our SGS model and then use it to investigate the
influence of turbulence on the plasmoid instability. We start the simulations
with Harris-type and force-free CS equilibria in the presence of a finite guide
field in the direction perpendicular to the reconnection plane. We use the DNS
results to investigate the growth of the plasmoid instability. The energy and
cross-helicity due to turbulence are obtained in terms of the mean fields by a
Gaussian filtering formulation from a Reynolds averaging turbulence model. The
influence of turbulence on the reconnection rate of the plasmoid instability is
investigated. To verify the predictions of the SGS-model, the electromotive
force (${\bf\cal{E}}$) is calculated for the coarse data obtained by filtering
and compared to the SGS-model. The symmetry breakage with respect to the guide
field direction causes a turbulent helicity which reduces the influence of the
apparent turbulent resistivity. The reduced reconnection rate of guide field
plasmoid reconnection is attributed to a balancing between the different
physical effects related to turbulence.
