On the development of a subgrid scale clutter model

The objective of this research is to develop a subgrid scale model to account for the effects of small objects, or "clutter", that are difficult to resolve using a CFD mesh. These objects may range in size from being small relative to the grid (i.e. porous media limit) to scales, which are on the same order as the grid size (i.e. a bluff body limit). Transport equations for momentum, turbulent kinetic energy and turbulent kinetic energy dissipation rate are derived based on time and spatial filtering concepts, introducing unknown correlations and surface integral terms that require explicit subgrid scale (SGS) model closures. The SGS models are formulated using a combination of well-established constitutive relations borrowed from the porous media literature and classical relations for drag on bluff bodies. The modeling methodology is exercised for two classes of problems. The first is flow in a porous media for which the obstructions are relatively dense. For this problem, predictions using the SGS clutter model are compared to established correlations taken from the porous media literature. The second class of problems is a cylinder in cross-flow for which both detailed experimental measurements and detailed CFD calculations of velocity deficit and kinetic energy profiles are available. Preliminary results indicate that this modeling approach offers a promising new approach to capture the macroscopic effects of small-scale objects without using excessive mesh resolution.