A Generalized Turbulence Forcing Method to Enable DNS at High Reynolds Numbers

The small-scale behaviour of turbulent flows is often studied using direct numerical simulations (DNS) of homogeneous isotropic turbulence, which need to be forced to achieve high Reynolds numbers and steady state statistics. However, most forcing techniques, meant to represent the effects of scales larger than the DNS domain, forgo the complexity of these energy containing scales and incorporate their effect merely through a single scalar energy injection rate parameter. We introduce a generalized method of forcing turbulence which extracts realistic large scale flow features from large eddy simulations through filtering, and imposes them onto a fully resolved grid in a specific subregion. The method is free from assumptions of equilibrium, isotropy, initial and boundary conditions, and is applicable to any realistic complex flow. The method is evaluated using both a priori and a posteriori analysis, as well as adaptive mesh refinement techniques, and is demonstrated to achieve accuracies comparable to a conventionally forced DNS at a fraction of the cost. Implications of the method for reacting flows involving large upscale transfer of kinetic energy are also discussed.