Large Eddy Simulations in Astrophysics
  In this review, the methodology of large eddy simulations (LES) is introduced
and applications in astrophysics are discussed. As theoretical framework, the
scale decomposition of the dynamical equations for neutral fluids by means of
spatial filtering is explained. For cosmological applications, the filtered
equations in comoving coordinates are also presented. To obtain a closed set of
equations that can be evolved in LES, several subgrid scale models for the
interactions between numerically resolved and unresolved scales are discussed,
in particular the subgrid scale turbulence energy equation model. It is then
shown how model coefficients can be calculated, either by dynamical procedures
or, a priori, from high-resolution data. For astrophysical applications,
adaptive mesh refinement is often indispensable. It is shown that the subgrid
scale turbulence energy model allows for a particularly elegant and physically
well motivated way of preserving momentum and energy conservation in AMR
simulations. Moreover, the notion of shear-improved models for inhomogeneous
and non-stationary turbulence is introduced. Finally, applications of LES to
turbulent combustion in thermonuclear supernovae, star formation and feedback
in galaxies, and cosmological structure formation are reviewed.
