  We present a one-equation subgrid scale model that evolves the turbulence
energy corresponding to unresolved velocity fluctuations in large eddy
simulations. The model is derived in the context of the Germano consistent
decomposition of the hydrodynamical equations. The eddy-viscosity closure for
the rate of energy transfer from resolved toward subgrid scales is localised by
means of a dynamical procedure for the computation of the closure parameter.
Therefore, the subgrid scale model applies to arbitrary flow geometry and
evolution. For the treatment of microscopic viscous dissipation a
semi-statistical approach is used, and the gradient-diffusion hypothesis is
adopted for turbulent transport. A priori tests of the localised eddy-viscosity
closure and the gradient-diffusion closure are made by analysing data from
direct numerical simulations. As an a posteriori testing case, the large eddy
simulation of thermonuclear combustion in forced isotropic turbulence is
discussed. We intend the formulation of the subgrid scale model in this paper
as a basis for more advanced applications in numerical simulations of complex
astrophysical phenomena involving turbulence.
